Copyright: PC Webopaedia 1.01, Copyright © 1996 Sandy Bay Software, Inc.
Citation: Copyright © 1996, Sandy Bay Software, Inc.


.INI File

Pronounced dot-in-ee file, a file that has a .INI extension and contains configuration information for MS-Windows. Two .INI files, WIN.INI and SYSTEM.INI, are required by MS-Windows. In addition, many applications have their own .INI files.


1-2-3

See Lotus 1-2-3.


286

Short for the Intel 80286 microprocessor.


3-D spreadsheet

See three-dimensional spreadsheet.


386

Short for the Intel 80386 microprocessor.


386SX

Short for the Intel 80386SX microprocessor.


3DO

A technology that supports photo-realistic graphics, full-motion video, and CD-quality sound. The first applications of this technology were stand-alone devices used for playing games, but the technology is beginning to find its way into PCs in the form of expansion boards.


486

Short for the Intel 80486 microprocessor.


4GL

See fourth-generation language.


680x0

See under Motorola microprocessors.


8086

Short for the Intel 8086 microprocessor.


8514/A

A high-resolution video standard for PCs developed by IBM in 1987. It is designed to extend the capabilities of VGA. The 8514/A standard provides a resolution of 1,024 by 768 pixels, which gives it about 2.5 times the pixels of VGA (640 by 480). Like VGA, 8514/A provides a palette of 262,000 colors, of which 256 can be displayed at one time. On monochrome displays, 8514/A provides 64 shades of gray.

In its original version, 8514/A relies on interlacing, a technique that makes it possible to provide resolution at low cost. Interlacing, however, carries a performance penalty, so many manufacturers produce noninterlaced 8514/A clones.

In 1990, IBM released the Extended Graphics Array (XGA) standard, which supersedes 8514/A.


A/UX

Pronounced ox, Apple’s version of UNIX, which runs on Macintoshes and PowerPCs.


abort

To stop a program or function before it has finished naturally. The term abort refers to both requested and unexpected terminations. For example, many applications let you abort a search or a print job by pressing a specified abort key. On the other hand, programs can abort unexpectedly for any of the following reasons:

•	bugs in the software

•	unexpected input that the program cannot handle

•	hardware malfunction

When a program aborts, you are usually returned to the operating system shell level. Contrast abort with crash, which makes the entire system, including the operating system, unusable.


absolute address

A fixed address in memory. The term absolute distinguishes it from a relative address, which indicates a location by specifying a distance from another location. Absolute addresses are also called real addresses and machine addresses.


absolute cell reference

In spreadsheet applications, a reference to a particular cell or group of cells that does not change, even if you change the shape or size of the spreadsheet, or copy the reference to another cell. For example, in Lotus 1-2-3 and other spreadsheet programs, the cell reference “$A$3” is an absolute cell reference that always points to the cell in the first column and third row. In contrast, the reference “A3” is a relative cell reference that initially points to the cell in the first column and third row, but may change if you copy the reference to another cell or change the shape and size of the spreadsheet in some other way. Absolute cell references are particularly useful for referencing constant values (i.e., values that never change).


accelerator board

A type of expansion board that makes a computer faster by adding a faster CPU or FPU. Accelerator boards provide a relatively inexpensive way to increase the performance of a computer.

There are many accelerator boards for Macintoshes and PCs. For example, a 486 accelerator board contains an Intel 80486 microprocessor. By adding it to an older PC with a 286 or 386 processor, you can effectively turn the computer into a 486 PC.

Note, however, that adding an accelerator board to a computer affects only the speed of the CPU (and sometimes main memory). This may not have a large effect on your applications if the limiting factors are the speed of the disk drive or the bus. If you want to increase performance of an old computer, you are probably better off buying a modern disk drive or adding extra memory.

Most modern computers are designed to accept simpler upgrades. Built into the motherboard is a socket in which the CPU sits. It is usually possible simply to remove the CPU and replace it with a faster model. This is particularly easy if the socket is a zero insertion force (ZIF) socket.


access

(v) (1) To use. For example, programs can access memory, which means they read data from or write data to main memory. A user can access files, directories, computers, or peripheral devices.

(2) More specifically, access often means to read data from or write data to a mass storage device. The time it takes to locate a single byte of information on a mass-storage device is called the access time.

(n) (1) The act of reading data from or writing data to a storage device.

(2) A privilege to use computer information in some manner. For example, a user might be granted read access to a file, meaning that the user can read the file but cannot modify or delete it. Most operating systems have several different types of access privileges that can be granted or denied to specific users or groups of users.


access code

Same as password, a series of characters and numbers that enables a user to access a computer.


access time

The time a program or device takes to locate a single piece of information and make it available to the computer for processing. DRAM (dynamic random access memory) chips for personal computers have access times of 50 to 150 nanoseconds (billionths of a second). Static RAM (SRAM) has access times as low as 10 nanoseconds. The access time of memory should be fast enough to keep up with the CPU. If not, the CPU will waste a certain number of clock cycles, which makes it slower.

Note, however, that reported access times can be misleading because most memory chips, especially DRAM chips, require a pause between back-to-back accesses. This is one reason why SRAM is so much faster than DRAM, even when the reported access times are equivalent; SRAM requires fewer refreshes, so the pause between back-to-back accesses is smaller. A more important measurement of a chip’s speed, therefore, is its cycle time, which measures how quickly two back-to-back accesses can be made.

Access time is also frequently used to describe the speed of disk drives. Disk access times are measured in milliseconds (thousandths of a second), often abbreviated as ms. Fast hard disk drives for personal computers boast access times of about 9 to 15 milliseconds. This means that the drive can make about 500 data accesses per second. Note that this is about 200 times slower than average DRAM.

The access time for disk drives (also called the seek time) refers to the time it actually takes for the read/write head to locate a sector on the disk. This is an average time since it depends on how far away the head is from the desired data. The performance of disk drives can be improved through special techniques such as caching and interleaving.


accessory slot

Same as expansion slot.


accounting software

A class of computer programs that perform accounting operations. The simplest accounting programs, sometimes called personal finance managers, are single-entry systems that automate check writing and record keeping.

Double-entry systems include functions for general ledger, accounts receivable, and accounts payable. More sophisticated systems also support functions for payroll, inventory, invoicing, and fixed assets. Some high-end systems even support sales analysis and time billing.


ACM

Abbreviation of the Association for Computing Machinery, an organization composed of U.S. computer professionals. Founded in 1947, the ACM publishes information relating to computer science, holds seminars, and creates and promotes computer standards.


acoustic coupler

A device onto which a telephone handset is placed to connect a computer with a network. The acoustic coupler might also contain a modem, or the modem could be a separate device.

Popular in the 1970s, acoustic couplers are no longer widely used. Nowadays, telephones connect directly to a modem via modular telephone connectors. This produces better connections than acoustic couplers and avoids the problems produced by irregularly shaped telephones. Still, acoustic coupler modems are useful in some situations, such as in hotel rooms where the telephone cable is anchored to the wall. Modems that do not use an acoustic coupler are sometimes called direct-connect modems.


Acrobat

A suite of programs developed by Adobe Systems, Inc. for creating and distributing electronic documents.  Programs in the suite allow you to create a PDF file for a document.  You can then distribute the PDF file electronically to people who view the document with the Acrobat Reader.  The reader is the best known component of the Acrobat suite and is freely distributed.

People viewing a PDF file (or document) with the Acrobat reader see the document with the exact layout intended by the author. This is its main advantage over other electronic formats such as HTML, where the layout can vary depending on the software being used.


active

Refers to objects currently being displayed or used. For example, in graphical user interfaces, the active window is the window currently receiving mouse and keyboard input. In spreadsheet applications, the active cell is the cell, usually highlighted, in which data can be entered or modified. The active program is the program currently running. When you enter a command, it usually applies only to the active elements.


active matrix display

A type of flat-panel display in which the screen is refreshed more frequently than in conventional passive-matrix displays. The most common type of active-matrix display is based on a technology known as TFT (thin film transistor). The two terms, active matrix and TFT, are often used interchangeably.


ActiveX

A technology developed by Microsoft for sharing information among different applications. ActiveX is an outgrowth of two other Microsoft technologies called OLE (Object Linking and Embedding) and COM (Component Object Model). ActiveX supports new features that enable it to take advantage of the Internet. For example, an ActiveX control can be automatically downloaded and executed by a Web browser. ActiveX is not a programming language, but rather a set of rules for how applications should share information. Programmers can develop ActiveX controls in a variety of languages, including C , C++, Visual Basic, and Java.

An ActiveX control is similar to a Java applet. Unlike Java applets, however, ActiveX controls have full access to the Windows operating system. This gives them much more power than Java applets, but with this power comes a certain risk that the applet may damage software on your machine. To control this risk, Microsoft developed a registration system so that browsers can identify and authenticate an ActiveX control before downloading it. Another difference between Java applets and ActiveX controls is that Java applets run on all platforms, whereas ActiveX controls are currently limited to Windows environments.

Related to ActiveX is a scripting language called VBScript that enables Web authors to embed interactive elements in HTML documents. Just as JavaScript is similar to Java, so VBScript is similar to Visual Basic. Currently, Microsoft's Web browser, Internet Explorer, supports Java, JavaScript, and ActiveX, whereas Netscape's browsers support only Java and JavaScript.


Ada

A high-level programming language developed in the late 1970s and early 1980s for the United States Defense Department. Ada was designed to be a do-everything language, from business applications to rocket guidance systems. One of its principal features is that it supports real-time applications. In addition, Ada incorporates modular techniques that make it easier to build and maintain large systems. Since 1986, Ada has been the mandatory development language for most U.S. military applications.

Ada is named after Augusta Ada Byron (1815−52), daughter of Lord Byron, and Countess of Lovelace. She helped Charles Babbage develop programs for the analytic engine, the first mechanical computer. She is considered by many to be the world's first programmer.


adapter

(1) The circuitry required to support a particular device. For example, video adapters enable the computer to support graphics monitors, and network adapters enable a computer to attach to a network. Adapters can be built into the main circuitry of a computer or they can be separate add-ons that come in the form of expansion boards.

(2) Short for video adapter.


ADB

Abbreviation of Apple Desktop Bus, a type of communications pathway built into all versions of the Apple Macintosh computer since the SE. It is used to connect low-speed input devices such as the keyboard and mouse. ADB ports are designated with the  icon. A single ADB port can support as many as 16 simultaneous input devices.


add-in

(1) A component you can add to a computer or other device to increase its capabilities. Add-ins can increase memory or add graphics or communications capabilities to a computer. They can come in the form of expansion boards, cartridges, or chips. The term add-in is often used instead of add-on for chips you add to a board that is already installed in a computer. In contrast, add-on almost always refers to an entire circuit board.

(2) A software program that extends the capabilities of larger programs. For example, there are many Excel add-ins designed to complement the basic functionality offered by Excel. In the Windows environment, add-ins are becoming increasingly common thanks to OLE 2.0.


add-on

Refers to a product designed to complement another product. For example, there are numerous add-on boards available that you can plug into a personal computer to give it additional capabilities. Another term for add-on board is expansion board.

Add-on products are also available for software applications. For example, there are add-on report generation programs that attach to popular database products such as dBASE, giving them additional report-generation and graphics capabilities.

The terms add-on and add-in are often, but not always, used synonymously. The term add-in can refer to individual chips you can insert into boards that are already installed in your computer. Add-on, on the other hand, almost always refers to an entire circuit board, cartridge, or program.


add-on board

Same as expansion board.


address

(1) A location of data, usually in main memory or on a disk. You can think of computer memory as an array of storage boxes, each of which is one byte in length. Each box has an address (a unique number) assigned to it. By specifying a memory address, programmers can access a particular byte of data. Disks are divided into tracks and sectors, each of which has a unique address. Usually, you do not need to worry about addresses unless you are a programmer.

(2) A name or token that identifies a network component. In local area networks (LANs), for example, every node has a unique address. On the Internet, every file has a unique address called a URL.


address bus

A collection of wires connecting the CPU with main memory that is used to identify particular locations (addresses) in main memory. The width of the address bus (that is, the number of wires) determines how many unique memory locations can be addressed. Modern PCs and Macintoshes have 24 address lines, which enables them to access 16MB (megabytes) of main memory.


address space

The set of all legal addresses in memory for a given application. The address space represents the amount of memory available to a program. Interestingly, the address space can be larger than physical memory through a technique called virtual memory.


Adobe Acrobat

See under Acrobat.


Adobe PostScript

See PostScript.


aggregate function

A function that performs a computation on a set of values rather than on a single value. For example, finding the average or mean of a list of numbers is an aggregate function.

All database management and spreadsheet systems support a set of aggregate functions that can operate on a set of selected records or cells.


AI

Abbreviation of artificial intelligence.


AIX

Acronym for Advanced Interactive eXecutive, a version of UNIX produced by IBM. AIX runs on a variety of computers, including PCs and workstations.


alert box

A small box that appears on the display screen to give you information or to warn you about a potentially damaging operation. For example, it might warn you that the system is deleting one or more files. Unlike dialog boxes, alert boxes do not require any user input. However, you need to acknowledge the alert box by pressing the Enter key or clicking a mouse button to make it go away.

Alert boxes are also called message boxes.


algorithm

A formula or set of steps for solving a particular problem. To be an algorithm, a set of rules must be unambiguous and have a clear stopping point. Algorithms can be expressed in any language, from natural languages like English or French to programming languages like FORTRAN.

We use algorithms every day. For example, a recipe for baking a cake is an algorithm. Most programs, with the exception of some artificial intelligence applications, consist of algorithms. Inventing elegant algorithms — algorithms that are simple and require the fewest steps possible — is one of the principal challenges in programming.


alias

(1) An alternative name for an object, such as a variable, file, or device. On Macintoshes, you can assign aliases for files, which allows you to have icons for the same file in different folders. Windows provides the same functionality but does not use the term alias.


aliasing

(1) In computer graphics, the process by which smooth curves and other lines become jagged because the resolution of the graphics device or file is reduced.

(2) In digital sound, aliasing is a static distortion resulting from a low sampling rate–below 40 kilohertz (Khz).


alignment

(1) When used to describe text, alignment is the arrangement of text or graphics relative to a margin. For example:

flush left alignment means that text is lined up along the left margin.	flush right alignment lines up text along the right margin.
centered alignment means that text is aligned around a midpoint.	justified alignment means that text lines up along both margins.
(2) In reference to graphical objects, alignment describes their relative positions. Most draw programs support an align command that allows you to align two or more objects so that their tops, bottoms, sides, or middles are aligned.


Alpha Processor

A RISC processor developed by Digital Equipment Corporation used in their line of workstations.


alphanumeric

Describes the combined set of all letters in the alphabet and the numbers 0 through 9 . It is useful to group letters and numbers together because many programs treat them identically, and differently from punctuation characters. For example, most operating systems allow you to use any letters or numbers in filenames but prohibit many punctuation characters. Your computer manual would express this rule by stating: “Filenames may be composed of alphanumeric characters.”

Sometimes additional characters are considered alphanumeric. For example, on IBM mainframes the characters @, #, and $ are considered alphanumeric characters.


Alt key

Short for Alternate key, the Alt key is like a second Control key. Not all computer keyboards have an Alt key, but it is standard on all PCs. You use it in the same fashion as the Control key—holding it down while you press another key. For example, an instruction to use the Alt+P combination means that you should hold the Alt key down while pressing and then releasing the P key. The meaning of any Alt key combination depends on which application is running.

On Macintoshes, the equivalent key is called the Option key.


Alta Vista

The name of a software firm associated with Digital Equipment Corporation (DEC).  Alta Vista offers software products you can use to locate and manage information on the Internet or a private computer network that uses Internet tools (an intranet).  The best known product from this company is the Alta Vista Search system that anyone can use to find information on the World Wide Web. People often use the term Alta Vista to refer to this free search service.

The Alta Vista search service contains one of the largest Web indices.  The index is maintained and generated by programs, called robots, that follow links on Web pages, download the pages, and then index them according to the words and phrases that the pages contain.


ALU

Abbreviation of arithmetic logic unit, the part of a computer that performs all arithmetic computations, such as addition and multiplication, and all comparison operations. The ALU is one component of the CPU (central processing unit).


America Online

A popular online service. It is often abbreviated as AOL.


American National Standards Institute

See ANSI.


American Standard Code for Information Interchange

See ASCII.


Amiga

A family of personal computers produced by Commodore Business Machines. Amigas are powerful personal computers that have extra microprocessors to handle graphics and sound generation. They also have built-in MIDI interfaces for connecting to synthesizers and other electronic musical devices. Like older Apple Macintosh computers, the Amiga line of computers is built around the Motorola 680x0 line of microprocessors. Amiga computers, however, are not compatible with Macintoshes because they use different operating systems. Nor are they compatible with PCs.

Faced with financial hardships, commodore sold the Amiga to a German company called Escom AG. Escom, in turn, also went bankrupt, and sold the Amiga design to a Chicago-based company called VIScorp. It remains to be seen whether VIScorp can revitalize the Amiga.


analog

Almost everything in the world can be described or represented in one of two forms: analog or digital. The principal feature of analog representations is that they are continuous. In contrast, digital representations consist of values measured at discrete intervals.

Digital watches are called digital because they go from one value to the next without displaying all intermediate values. Consequently, they can display only a finite number of times of the day. In contrast, watches with hands are analog, because the hands move continuously around the clock face. As the minute hand goes around, it not only touches the numbers 1 through 12, but also the infinite number of points in between.

Early attempts at building computers used analog techniques, but accuracy and reliability were not good enough. Today, almost all computers are digital.


analog monitor

The traditional type of color display screen that has been used for years in televisions. In reality, all monitors based on CRT technology (that is, all monitors except flat-panel displays) are analog. Some monitors, however, are called digital monitors because they accept digital signals from the video adapter. EGA monitors, for example, must be digital because the EGA standard specifies digital signals. Digital monitors must nevertheless translate the signals into an analog form before displaying images. Some monitors can accept both digital and analog signals.

Most analog monitors are designed to accept signals at a precise frequency. They are therefore called fixed-frequency monitors. However, a special type of monitor, called a multiscanning or multisync monitor, automatically adjusts itself to the frequency of the signals being sent to it. A third type of monitor, called a multifrequency monitor, is designed to accept signals at two or more preset frequency levels.


anchor

In desktop publishing, to fix a graphical object so that its position relative to some other object remains the same during repagination. Frequently, for example, you may want to anchor a picture next to a piece of text so that they always appear together.


AND operator

A Boolean operator that returns a value of TRUE if both its operands are TRUE, and FALSE otherwise.


animation

A simulation of movement created by displaying a series of pictures, or frames. Cartoons on television, for example, is one example of animation. Animation on computers is one of the chief ingredients of multimedia presentations. There are many software applications that enable you to create animations that you can display on a computer monitor.

Note the difference between animation and video. Whereas video takes continuous motion and breaks it up into discrete frames, animation starts with independent pictures and puts them together to form the illusion of continuous motion.


annotation

A comment attached to a particular section of a document. Many computer applications enable you to enter annotations on text documents, spreadsheets, presentations, and other objects. This is a particularly effective way to use computers in a workgroup environment to edit and review work. The creator of a document sends it to reviewers who then mark it up electronically with annotations and return it. The document’s creator then reads the annotations and adjusts the document appropriately.

Many modern applications support voice annotations. If the computer is equipped with a microphone, the reviewer can voice his comments orally instead of writing them. These voice annotations are digitized and stored with the document. When a reader of the document selects the annotation icon, the spoken message is played back through the computer’s speakers.


ANSI

Acronym for the American National Standards Institute. Founded in 1918, ANSI is a voluntary organization composed of over 1,300 members (including all the large computer companies) that creates standards for the computer industry. For example, ANSI C is a version of the C language that has been approved by the ANSI committee. To a large degree, all ANSI C compilers, regardless of which company produces them, should behave similarly.

In addition to programming languages, ANSI sets standards for a wide range of technical areas, from electrical specifications to communications protocols. For example, FDDI, the main set of protocols for sending data over fiber optic cables, is an ANSI standard.


ANSI Character Set

A collection of special characters and associated codes adopted by the ANSI standards organization . The ANSI character set includes many foreign characters, special punctuation, and business symbols.

In Windows environments, you can enter ANSI characters by holding down the Alt key and typing the ANSI code with the numeric keypad. On Macintoshes, you can enter ANSI characters by holding down the Option key and typing a character.


ANSI.SYS

Pronounced ann-see-dot-siss, the name of a DOS device driver that makes a monitor conform to the ANSI standard. The ANSI standard specifies a series of escape sequences that cause the monitor to behave in various ways. For example, one escape sequence clears the screen while another causes all subsequent characters to be inverted.

In general, DOS programs do not use the ANSI codes because these codes are slower than the built-in BIOS codes. DOS programs that do use ANSI codes for compatibility with other devices require that you load the ANSI.SYS device driver in the configuration file, CONFIG.SYS.


answer-only modem

A modem that can receive messages but cannot send them. Only the most inexpensive modems are answer-only.


antialiasing

In computer graphics, antialiasing is a software technique for diminishing jaggies—stairsteplike lines that should be smooth. Jaggies occur because the output device, the monitor or printer, doesn't have a high enough resolution to represent a smooth line. Antialiasing reduces the prominence of jaggies by surrounding the stairsteps with intermediate shades of gray (for gray-scaling devices) or color (for color devices). Although this reduces the jagged appearance of the lines, it also makes them fuzzier.

Another method for reducing jaggies is called smoothing, in which the printer changes the size and horizontal alignment of dots to make curves smoother.


antistatic mat

A mat on which you can stand while repairing a computer or adding expansion cards. The mat absorbs static electricity which might otherwise damage electronic components. Another way to eliminate damage caused by static electricity is to wear an antistatic wristband.


antivirus program

A utility that searches a hard disk for viruses and removes any that are found.


AOL

See America Online.


API

Abbreviation of application program interface, a set of routines, protocols, and tools for building software applications. A good API makes it easier to develop a program by providing all the building blocks. A programmer puts the blocks together.

Most operating environments, such as MS-Windows, provide an API so that programmers can write applications consistent with the operating environment. Although APIs are designed for programmers, they are ultimately good for users because they guarantee that all programs using a common API will have similar interfaces. This makes it easier for users to learn new programs.


app

Short for application. A killer app, for example, is an application that surpasses (i.e., kills) its competitors.


append

(1) To add something at the end. For example, you can append one file to another or you can append a field to a record. Do not confuse append with insert. Append always means to add at the end. Insert means to add in between.


Apple Computer

A personal computer company founded in 1976 by Steven Jobs and Steve Wozniak. Throughout the history of personal computing, Apple has been one of the most innovative influences. In fact, some analysts say that the entire evolution of the PC can be viewed as an effort to catch up with the Apple Macintosh.

In addition to inventing new technologies, Apple also has often been the first to bring sophisticated technologies to the personal computer. Apple’s innovations include:

Graphical user interface (GUI). First introduced in 1983 on its Lisa computer. Many components of the Macintosh GUI have become de facto standards and can be found in other operating systems, such as Microsoft Windows.

Color. The Apple II, introduced in 1977, was the first personal computer to offer color monitors.

Built-in networking. In 1985, Apple released a new version of the Macintosh with built-in support for networking (LocalTalk).

Plug & play expansion. In 1987, the Mac II introduced a new expansion bus called NuBus that made it possible to add devices and configure them entirely with software.

QuickTime. In 1991, Apple introduced QuickTime, a multi-platform standard for video, sound, and other multimedia applications.

Integrated television. In 1993, Apple released the Macintosh TV, the first personal computer with built-in television and stereo CD.

RISC. In 1994, Apple introduced the Power Mac, based on the PowerPC RISC microprocessor.


Apple Desktop bus

See ADB.


Apple key

A special key on Macintosh computers labeled with the Apple logo (picture here). On all but the oldest Apple computers, the Apple key serves as the Command key.


Apple Macintosh computer

See Macintosh computer.


applet

A program designed to be executed from within another application. Unlike an application, applets cannot be executed directly from the operating system. With the growing popularity of OLE (object linking and embedding), applets are becoming more prevalent. A well-designed applet can be invoked from many different applications.


AppleTalk

An inexpensive local-area network (LAN) architecture built into all Apple Macintosh computers and laser printers. AppleTalk is based on a bus topology. The original version can connect up to 32 devices within a distance of about 1,000 feet. An updated version, known as Phase 2, can support 16 million devices.

Although AppleTalk is relatively slow (230 thousand bits per second) compared with other networks such as Ethernet (10 million bits per second) and the IBM Token Ring (4 million bits per second), it is popular because it is inexpensive and simple. It can connect Macintosh computers and printers, and even PCs if they are equipped with special AppleTalk hardware and software.

The standard cabling scheme for AppleTalk networks is known as LocalTalk. However, AppleTalk can be used with other cabling schemes as well.


application

A program or group of programs designed for end users. Software can be divided into two general classes: systems software and applications software. Systems software consists of low-level programs that interact with the computer at a very basic level. This includes operating systems, compilers, and utilities for managing computer resources.

In contrast, applications software (also called end-user programs) includes database programs, word processors, and spreadsheets. Figuratively speaking, applications software sits on top of systems software because it is unable to run without the operating system and system utilities.


Application Program Interface

See API.


ARC

To compress a file using the ARC format. The ARC data compression format, created by Systems Enhancement Associates, is particularly popular among bulletin board systems (BBSs). Another common format is ZIP.

Files that have been compressed with an ARC utility end with a .ARC extension. To decompress them, you need a utility called ARC-E (stands for arc-extract).


Archie

A program that enables you to search for files anywhere on the Internet by filename.


architecture

A design. The term architecture can refer to either hardware or software, or to a combination of hardware and software. The architecture of a system always defines its broad outlines, and may define precise mechanisms as well.

An open architecture allows the system to be connected easily to devices and programs made by other manufacturers. Open architectures use off-the-shelf components and conform to approved standards. A system with a closed architecture, on the other hand, is one whose design is proprietary, making it difficult to connect the system to other systems.


archival backup

A type of backup in which only files modified since the last backup are copied. Archival backups are much faster than full backups because fewer files are copied. Typically, users make a full backup of all data once a week and an archival backup each day between the full backups.

Archival backups are also called incremental backups.


archive

(v) (1) To copy files to a long-term storage medium for backup. Large computer systems often have two layers of backup, the first of which is a disk drive. Periodically, the computer operator will archive files on the disk to a second storage device, usually a tape drive.

On smaller systems, archiving is synonymous with backing up.

(2) To compress a file.

(n) (1) A disk, tape, or directory that contains files that have been backed up.

(2) A file that contains one or more files in a compressed format.

(adj) In DOS systems, the archive attribute marks files that have been modified since the last backup.


ARCnet

Short for Attached Resource Computer network, ARCnet is one of the oldest, simplest, and least expensive types of local-area network. ARCnet was introduced by Datapoint Corporation in 1968. It uses a token-ring architecture, supports data rates of 2.5 megabits per second, and connects up to 255 computers. A special advantage of ARCnet is that it permits various types of transmission media—twisted-pair wire, coaxial cable, and fiber optic cable—to be mixed on the same network.

Although it has less capacity than other networks such as Ethernet and IBM Token Ring, it is nevertheless extremely popular because of its simplicity. A new specification, called ARCnet Plus, will support data rates of 20 megabits per second.


area chart

A type of presentation graphic that emphasizes a change in values by filling in the portion of the graph beneath the line connecting various data points.


argument

In programming, a value that you pass to a routine. For example, if SQRT is a routine that returns the square root of a value, then SQRT(25) would return the value 5. The value 25 is the argument.

Argument is often used synonymously with parameter, although parameter can also mean any value that can be changed. In addition, some programming languages make a distinction between arguments, which are passed in only one direction, and parameters, which can be passed back and forth, but this distinction is by no means universal.

An argument can also be an option to a command, in which case it is often called a command-line argument.


arithmetic expression

An expression that represents a numeric value. Other types of expressions can represent character or Boolean values.


arithmetic operator

See under operator.


ARPANET

The precursor to the Internet, ARPANET was a large wide-area network created by the United States Defense Advanced Research Project Agency (ARPA). Established in 1969, ARPANET served as a testbed for new networking technologies, linking many universities and research centers.


array

A series of objects all of which are the same size and type. Each object in an array is called an array element. For example, you could have an array of integers or an array of characters or an array of anything that has a defined data type. The important characteristics of an array are:

•	Each element has the same data type (although they may have different values).

•	The entire array is stored contiguously in memory (that is, there are no gaps between elements).

Arrays can have more than one dimension. A one-dimensional array is called a vector; a two-dimensional array is called a matrix. To access a particular element in an array, you need to specify the array's name with one or more subscripts. For example:

A[5]

specifies the fifth element in a one-dimensional array named A.


arrow keys

Most computer keyboards contain four arrow keys for moving the cursor or insertion point right, left, up, or down. When combined with the Shift, Function, Control, or Alt keys (on PCs), the arrow keys can have different meanings. For example, pressing Shift+Up-arrow might move the cursor or pointer up an entire page. On Macintoshes, the arrow keys can be combined with the Shift, Option, and Command keys.

The exact manner in which the arrow keys function depends on which program is running. Some programs ignore them.

The arrow keys are also called cursor control keys.


artificial intelligence

The branch of computer science concerned with making computers behave like humans. The term was coined in 1956 by John McCarthy at the Massachusetts Institute of Technology. Artificial intelligence includes

games playing: programming computers to play games such as chess and checkers

expert systems: programming computers to make decisions in real-life situations (for example, some expert systems help doctors diagnose diseases based on symptoms)

natural language: programming computers to understand natural human languages

neural networks: Systems that simulate intelligence by attempting to reproduce the types of physical connections that occur in animal brains

robotics: programming computers to see and hear and react to other sensory stimuli

Currently, no computers exhibit full artificial intelligence (that is, are able to simulate human behavior). The greatest advances have occurred in the field of games playing. The best computer chess programs are now capable of beating most humans, although they still lose to grand masters.

In the area of robotics, computers are now widely used in assembly plants, but they are capable only of very limited tasks. Robots have great difficulty identifying objects based on appearance or feel, and they still move and handle objects clumsily.

Natural-language processing offers the greatest potential rewards because it would allow people to interact with computers without needing any specialized knowledge. You could simply walk up to a computer and talk to it. Unfortunately, programming computers to understand natural languages has proved to be more difficult than originally thought. Some rudimentary translation systems that translate from one human language to another are in existence, but they are not nearly as good as human translators. There are also voice recognition systems that can convert spoken sounds into written words, but they do not understand what they are writing; they simply take dictation. Even these systems are quite limited—you must speak slowly and distinctly.

In the early 1980s, expert systems were believed to represent the future of artificial intelligence and of computers in general. To date, however, they have not lived up to expectations. Many expert systems help human experts in such fields as medicine and engineering, but they are very expensive to produce and are helpful only in special situations.

Today, the hottest area of artificial intelligence is neural networks, which are proving successful in a number of disciplines such as voice recognition and natural-language processing.

There are several programming languages that are known as AI languages because they are used almost exclusively for AI applications. The two most common are LISP and PROLOG.


ascender

In typography, the portion of a lowercase letter that rises above the main body of the letter (that is, above the height of a lowercase x).


ASCII

Acronym for the American Standard Code for Information Interchange. Pronounced ask-ee, ASCII is a code for representing English characters as numbers, with each letter assigned a number from 0 to 127. For example, the ASCII code for uppercase M is 77. Most computers use ASCII codes to represent text, which makes it possible to transfer data from one computer to another.

Text files stored in ASCII format are sometimes called ASCII files. Text editors and word processors are usually capable of storing data in ASCII format, although ASCII format is not always the default storage format. Most data files, particularly if they contain numeric data, are not stored in ASCII format. Executable programs are never stored in ASCII format.

The standard ASCII character set uses just 7 bits for each character. A larger character set, known as extended ASCII or high ASCII, uses 8 bits, which gives it 128 additional characters.The extra characters are used to represent non-English characters, graphics symbols, and mathematical symbols. The extended characters and their ASCII codes have been defined by IBM, but they have not been officially standardized.

The ANSI standards organization has defined a character set that overlaps the extended character set, but uses different codes (see under ANSI character set).

Another set of codes that is used on large IBM computers is EBCDIC.


ASCII file

A text file in which each byte represents one character according to the ASCII code. Contrast with a binary file, in which there is no one-to-one mapping between bytes and characters. Files that have been formatted with a word processor must be stored and transmitted as binary files to preserve the formatting. ASCII files are sometimes called plain text files.


aspect ratio

In computer graphics, the relative horizontal and vertical sizes. For example, if a graphic has an aspect ratio of 2:1, it means that the width is twice as large as the height. When resizing graphics, it is important to maintain the aspect ratio to avoid stretching the graphic out of proportion.


assembler

A program that translates programs from assembly language to machine language.


assembly language

A programming language that is once removed from a computer's machine language. Machine languages consist entirely of numbers and are almost impossible to read and write. Assembly languages have the same structure and set of commands as machine languages, but they enable a programmer to use names instead of numbers.

Each type of CPU has its own machine language and assembly language, so an assembly language program written for one type of CPU won’t run on another. In the early days of programming, all programs were written in assembly language. Now, most programs are written in a high-level language such as FORTRAN or C. Programmers still use assembly language when speed is essential or when they need to perform an operation that isn't possible in a high-level language.


assign

To give a value to a variable. In programming, you assign a value to a variable with a special symbol called an assignment operator. In many languages, the assignment operator is the equal sign (=). For example, the following C language statement assigns the value 5 to the variable x:

x = 5

Such a statement is called an assignment statement.


associate

To link a certain type of file to a specific application. In MS-DOS and Microsoft Windows environments, the file’s type is specified by its three-character extension. For example, the .DOC extension identifies Microsoft Word documents. Once a file type has been associated with an application, selecting any file of that type automatically starts its associated application and loads the selected file.


Association for Computing Machinery

See under ACM.


asterisk

Also called a star, a punctuation mark denoted by a 6-pointed snowflake shape (*). In many operating systems and applications, the asterisk is used as a wild card symbol to represent any string of characters.


async

Short for asynchronous.


asynchronous

Not synchronized; that is, not occurring at predetermined or regular intervals. The term asynchronous is usually used to describe communications in which data can be transmitted intermittently rather than in a steady stream. For example, a telephone conversation is asynchronous because both parties can talk whenever they like. If the communication were synchronous, each party would be required to wait a specified interval before speaking.

The difficulty with asynchronous communications is that the receiver must have a way to distinguish between valid data and noise. In computer communications, this is usually accomplished through a special start bit and stop bit at the beginning and end of each piece of data. For this reason, asynchronous communication is sometimes called start-stop transmission.

Most communications between computers and devices are asynchronous.


Asynchronous Transfer Mode

See ATM.


AT

Short for advanced technology, the AT is an IBM PC model introduced in 1984. It includes an Intel 80286 microprocessor, a 1.2MB floppy drive, and an 84-key AT keyboard.

Today, the term is used more generally to refer to any PC with an 80286 processor.


AT bus

The expansion bus on the IBM PC/AT and compatible computers. The bus is the collection of wires and electronic components that connect all device controllers and add-in cards. The controllers are the components that attach to peripheral devices. The bus, therefore, is the main highway for all data moving in and out of the computer.

The AT bus, which runs at 8 megahertz and has a 16-bit data path, is the de facto standard for PCs. Because all IBM PCs (until the high-end PS/2 models) had an AT bus, it has been possible for manufacturers to produce expansion boards that will work with any PC.

As processors have become more powerful, and applications more demanding, the AT bus has turned out to be the chief bottleneck in PCs. In response, IBM introduced the Micro Channel Architecture (MCA) in 1987. However, MCA was not accepted by the computer industry because it was not backward compatible with the AT-bus, so IBM has been forced to drop it.

A more successful alternative to the AT bus is the Extended Industry Standard Architecture (EISA), a high-speed 32-bit bus architecture developed by a group of IBM’s competitors. Unlike MCA, EISA is backward compatible with the AT bus, so a computer equipped with an EISA bus can accept AT or EISA expansion boards.

While EISA has had limited success, its speeds are still insufficient for modern graphical applications. The most common solution to bypassing the AT-bus bottleneck is to include a local bus on the motherboard. A local bus communicates directly with the processor rather than using the standard computer bus. Currently, there are two competing standards for local buses: VESA local bus (VL-bus), promoted by the VESA standards group, and Peripheral Component Interconnect (PCI), designed and promoted by Intel.

The AT bus is sometimes referred to as the ISA bus, which stands for Industry Standard Architecture. However, ISA also includes the XT bus, which is an 8-bit version of the AT bus.


AT command set

Pronounced ay-tee command set, the de facto standard language for controlling modems. The AT command set was developed by Hayes and is recognized by virtually all personal computer modems.


AT keyboard

An 84-key keyboard introduced with the PC/AT. It was later replaced with the 101-key Enhanced Keyboard.


ATM

Short for Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size.  The cell used with ATM is relatively small compared to units used with older technologies.  The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line.

Current implementations of ATM support support data transfer rates of from 25 to 622 Mbps (megabits per second). This compares to a maximum of 100 Mbps for Ethernet, the current technology used for most LANs.


Attached Resource Computer Network

See ARCnet.


attribute

(1) A characteristic. In a word processing application, an underlined word would be said to have the underline attribute. In database systems, a field can have various attributes. For example, if it contains numeric data, it has the numeric attribute.

(2) In database management  systems, the term attribute is sometimes used as a synonym for field.

(3) In DOS systems, every file has a file attribute that indicates several properties of the file. For example, the file attribute indicates whether the file is read-only, whether it needs to be backed up, and whether it is visible or hidden.


audio card

Same as sound card.


audit trail

A record showing who has accessed a computer system and what operations he or she has performed during a given period of time. Audit trails are useful both for maintaining security and for recovering lost transactions. Most accounting systems and database management systems include an audit trail component. In addition, there are separate audit trail software products that enable network administrators to monitor use of network resources.


authoring tool

A program that helps you write hypertext or multimedia applications. Authoring tools usually enable you to create a final application merely by linking together objects, such as a paragraph of text, an illustration, or a song. By defining the objects' relationships to each other, and by sequencing them in an appropriate order, authors (those who use authoring tools) can produce attractive and useful graphics applications. Most authoring systems also support a scripting language for more sophisticated applications.

The distinction between authoring tools and programming tools is not clear-cut. Typically, though, authoring tools require less technical knowledge to master and are used exclusively for applications that present a mixture of textual, graphical, and audio data.


auto-answer

A feature supported by many modems that enables your computer to accept incoming calls even if you are not present. In auto-answer mode, a modem attempts to establish a connection whenever the telephone rings. This is an important feature if you are offering a service to which others can subscribe.

Auto-answer is also a critical feature for fax modems because it enables you to receive fax documents while you are away. All fax machines are auto-answer.


auto-redial

A feature supported by many modems that causes the modem to continue redialing a number until it makes a connection. This is a useful feature if you subscribe to an online service that is frequently busy.


auto-repeat

A feature of some keys on computer keyboards that causes them to repeat as long as they are held down. Most keys are auto-repeat.


autoexec.bat

Stands for automatically executed batch file, the file that DOS automatically executes when a computer boots up. This is a convenient place to put commands you always want to execute at the beginning of a computing session. For example, you can set system parameters such as the date and time, and install memory-resident programs.


automatic acceleration

See under dynamic acceleration.


automatic recalculation

In spreadsheets, a mode in which all cells are recalculated whenever a value changes. Automatic recalculation ensures that the spreadsheet data is always up-to-date, but it may make working on the spreadsheet slower. Alternatively, you can specify manual recalculation, where you must explicitly instruct the application to recalculate.


autosave

A feature supported by many applications in which the program automatically saves data files at predetermined intervals. This is an important feature because it reduces the amount of work you would lose if your system crashed. Usually, you can specify how often you want the application to save data.


autosizing

Refers to a monitor's ability to accept signals at one resolution and display the image at a different resolution. For example, a VGA video card outputs images at a resolution of 640 by 480. An SVGA monitor, however, can display images at a resolution of only 800 by 600, or even 1,024 by 768. If the monitor supports autosizing, it automatically adjusts the size of the image so that the proportions are correct. Without autosizing, you need to adjust an image manually so that it fills the screen properly.


autosync monitor

Same as multiscanning monitor.


autotracing

The process of converting a bit-mapped image (or raster image) into a vector image. In a bit-mapped image, each object is represented by a pattern of dots, while in a vector image every object is defined geometrically.

Most autotracing packages read files in a variety of bit-mapped formats (PCX and TIFF are the most common) and produce a file in a vector format such as Encapsulated PostScript (EPS). The conversion techniques used, and the accuracy of the conversion process, differ from one package to another.

Autotracing is particularly useful for manipulating images produced by an optical scanner. Scanners produce bit-mapped images that cannot be manipulated by sophisticated tools until they have been converted into a vector format through autotracing.


AUX

Stands for Auxiliary port, the logical name in DOS systems for the standard communications port. This is usually the same as COM1.


AVI

Short for Audio Video Interleave, the file format for Microsoft’s Video for Windows standard. See under Video for Windows.


B-ISDN

See broadband ISDN.


back end

See under front end.


backbone

Another term for bus, the main wire that connects nodes.


background

(1) Multitasking computers are capable of executing several tasks, or programs, at the same time. In some multitasking systems, one of the processes is called the foreground process, and the others are called background processes.

The foreground process is the one that accepts input from the keyboard, mouse, or other input device. Background processes cannot accept interactive input from a user, but they can access data stored on a disk and write data to the video display. For example, some word processors print files in the background, enabling you to continue editing while files are being printed. This is called print spooling. In addition, many communications programs are designed to run in the background. Background processes generally have a lower priority than foreground processes so that they do not interfere with interactive applications.

Even though DOS is not a multitasking operating system, it can perform some specialized tasks, such as printing, in the background. Operating environments, such as Microsoft Windows and the Macintosh operating system, provide a more general multitasking environment.

(2) The area of a display screen not covered by characters and graphics. The background is like a canvas on top of which characters and graphics are placed. Some monitors allow you to control the color or shading of the background. The background is also called the matrix.


backlighting

A technique used to make flat-panel displays easier to read. A backlit display is illuminated so that the foreground appears sharper in contrast with the background.


backslash

The backslash character is \; a simple slash or forward slash is /. In DOS and Windows systems, the backslash represents the root directory and is also used to separate directory names and filenames in a pathname.


backspace

A character that causes the cursor to move backward one character space, possibly deleting the preceding character. The backspace character has an ASCII value of 8. Most keyboards have a Backspace key that invokes this character. When inserted in a file, the character causes a printer or other device to move backward one space.


Backspace key

A key that moves the cursor or insertion point backward one character space. In addition to moving the cursor backward, the Backspace key usually deletes the character to the left of the cursor or insertion point. It is particularly useful, therefore, for correcting typos. Note that PCs also have a Delete key, which deletes the character under the cursor (or to the right of the insertion point). To move the cursor or insertion point backward without deleting characters, use the arrow keys.


backup

(v) To copy files to a second medium (a disk or tape) as a precaution in case the first medium fails. One of the cardinal rules in using computers is

Backup your files regularly.

Even the most reliable computer is apt to break down eventually. Many professionals recommend that you make two, or even three, backups of all your files. To be especially safe, you should keep one backup in a different location from the others.

You can back up files using operating system commands, or you can buy a special-purpose backup utility. In general, backup programs are much faster than operating system shell commands because they use a DMA channel. In addition, the backup programs often compress the data so that backups require fewer disks.

(n) (1) The act of backing up.

(2) A substitute or alternative. The term backup usually refers to a disk or tape that contains a copy of data.


backward compatible

Compatible with earlier models or versions of the same product. A new version of a program is said to be backward compatible if you can create a file with the new version and then use the file with an older version of the program. A computer is said to be backward compatible if it can run the same software as the previous model of the computer.

Backward compatibility is important because it eliminates the need to start over when you upgrade to a newer product. A backward-compatible word processor, for instance, allows you to edit documents created with a previous version of the program. In general, manufacturers try to keep all their products backward compatible. Sometimes, however, it is necessary to sacrifice backward compatibility to take advantage of a new technology.

The flip side of backward compatibility is upward compatibility. Upward compatible is the same as backward compatible, except that it is from the point of view of the older model.

Another term for backward compatible is downward compatible.


bad sector

A portion of a disk that cannot be used because it is flawed. When you format a disk, the operating system identifies any bad sectors on the disk and marks them so they will not be used. If a sector that already contains data becomes damaged, you will need special software to recover the data.

Almost all hard disks come with bad sectors (sectors damaged during the manufacturing process), so do not be alarmed if a utility reports that your hard disk has bad sectors. However, additional bad sectors should occur only infrequently if your drive is functioning properly. Floppy disks should not have any bad sectors.


BAK file

In DOS systems, a file with a .BAK extension, indicating that the file is a backup. Many applications produce BAK files as part of their autosave procedure. Periodically, you may want to search for BAK files and delete old ones.


ballistic tracking

See under dynamic acceleration.


bandwidth

The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits or bytes per second (bps). For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).

The bandwidth is particularly important for I/O devices. For example, a fast disk drive can be hampered by a bus with a low bandwidth. This is the main reason that new buses, such as EISA and PCI,  have been developed for the IBM PC.


bar chart

In presentation graphics, a type of graph in which different values are represented by rectangular bars.


base address

An address that serves as a reference point for other addresses. For example, a base address could indicate the beginning of a program. The address of every instruction in the program could then be specified by adding an offset to the base address. For example, the address of the fifth instruction would be the base address plus 5.


base memory

Same as conventional memory.


baseband transmission

A type of digital data transmission in which each medium (wire) carries only one signal, or channel, at a time. In contrast, broadband transmission enables a single wire to carry multiple signals simultaneously.

Most communications involving computers uses baseband transmission. This includes communications from the computer to devices (printers, monitors, and so on), communications via modems, and the majority of networks. An exception is B-ISDN networks, which use broadband transmission.


baseline

In typography, the imaginary line on which characters sit. The x-height of a font is measured from the baseline to the top of a lowercase x. The descender, for those characters that have one, is defined as the portion of the character that falls below the baseline.


BASIC

Acronym for Beginner's All-purpose Symbolic Instruction Code. Developed by John Kemeney and Thomas Kurtz in the mid 1960s at Dartmouth College, BASIC is one of the earliest and simplest high-level programming languages. During the 1970s, it was the principal programming language taught to students, and continues to be a popular choice among educators.

Despite its simplicity, BASIC is used for a wide variety of business applications. There is an ANSI standard for the BASIC language, but most versions of BASIC include many proprietary extensions. Microsoft’s popular Visual Basic, for example, adds many object-oriented features to the standard BASIC.

Recently, many variations of BASIC have appeared as programming, or macro, languages within applications. For example, Microsoft Word and Excel both come with a version of BASIC with which users can write programs to customize and automate these applications.


basic input/output system

See BIOS.


BAT file

In DOS systems, batch files are often called BAT files because their filenames end with a .BAT extension.


batch file

A file that contains a sequence, or batch, of commands. Batch files are useful for storing sets of commands that are always executed together because you can simply enter the name of the batch file instead of entering each command individually.

In DOS systems, batch files end with a .BAT extension. For example, the following DOS batch file prints the date and time and sets the prompt to GO>

date

time

prompt [GO>]

Whenever you boot a DOS-based computer, the system automatically executes the batch file named AUTOEXEC.BAT, if it exists.

Many operating systems use the terms command file or shell script in place of batch file.


batch processing

Executing a series of noninteractive jobs all at one time. The term originated in the days when users entered programs on punch cards. They would give a batch of these programmed cards to the system operator, who would feed them into the computer.

Usually, batch jobs are stored up during working hours and then executed during the evening or whenever the computer is idle. Batch processing is particularly useful for operations that require the computer or a peripheral device for an extended period of time. Once a batch job begins, it continues until it is done or until an error occurs. Note that batch processing implies that there is no interaction with the user while the program is being executed.

The opposite of batch processing is transaction processing or interactive processing. In interactive processing, the application responds to commands as soon as you enter them.


battery pack

A rechargeable battery used in portable computer devices, such as notebook computers. The most common substances used in computer battery packs are nickel cadmium (Nicad) and nickel metal hydride (NiMH). Another substance, being used in some newer batteries, is lithium.

A new type of battery, called a smart battery, provides the computer with information about its power status so that the computer can conserve power intelligently. With a normal battery, the computer makes estimates about the battery’s condition that are not always correct.


baud

Pronounced bawd, the number of electrical oscillations that occur each second. The term is named after J.M.E. Baudot, the inventor of the Baudot telegraph code.

At slow speeds, only one bit of information is encoded in each electrical change. The baud rate, therefore, indicates the number of bits per second that are transmitted. For example, a baud rate of 300 means that 300 bits are transmitted each second (abbreviated 300 bps). Assuming asynchronous communication, which requires 10 bits per character, this translates to 30 characters per second (cps). For slow rates (below 1,200 baud), you can divide the baud rate by 10 to see how many characters per second are sent.

At higher baud rates, it is possible to encode more than one bit in each electrical change. A baud rate of 4,800 may allow 9,600 bits to be sent each second. At high baud levels, therefore, data transmission rates are usually expressed in bits per second (bps) rather than in baud rates. For example, a 9,600 bps modem may operate at only 2,400 baud.


bay

Short for drive bay, this refers to a site in a personal computer where a hard or floppy disk drive, CD-ROM drive or tape drive can be installed. Thus, the number of drive bays in a computer determines how many mass storage devices can be internally installed.

For PCs, bays come in a variety of sizes, the most common being 3.5 inch, which represents the bay’s height. In addition, bays are described as either internal or exposed. An internal bay cannot be used for removable media, such as floppy drives. Some manufacturers use the terms hidden and accessible in place of internal and exposed.

Do not confuse bays with slots, which are openings in the computer where expansion boards can be installed.


BBS

See bulletin board system.


Bell 103

The de facto standard protocol in the United States for transmitting data over telephone lines at transmission rates of 300 baud. The Bell 103A standard defines asynchronous, full-duplex communication. Europe and Japan use the CCITT V.21 protocol.


Bell 212A

The de facto standard protocol in the United States for transmitting data over telephone lines at transmission rates of 1,200 bps. The Bell 212A standard defines asynchronous, full-duplex communications. Europe and Japan use the CCITT V.22 protocol.


bells and whistles

Fancy features provided by an application. Typically, the term refers to small features that are needed only in special cases or to features that make the program more visibly attractive (i.e., like real bells and whistles, are aimed at attracting your attention). Depending on the author, the term can be used either favorably or negatively. Many users and critics, for example, lament the increasing addition of bells and whistles that, they feel, make an application harder to learn and use without providing commensurate new functionality.


benchmark

A test used to compare performance of hardware and/or software. Many trade magazines have developed their own benchmark tests, which they use when reviewing a class of products. When comparing benchmark results, it is important to know exactly what the benchmarks are designed to test. A benchmark that tests graphics speed, for example, may be irrelevant to you if the type of graphical applications you use are different from those used in the test.


Bernoulli disk drive

Named after a Swiss scientist who discovered the principle of aerodynamic lift, the Bernoulli disk drive is a special type of floppy disk drive from Iomega Corporation that is faster and has greater storage capacity than traditional floppy drives.

A Bernoulli drive is really a cross between a hard disk drive and floppy drive. Like the platters in hard disk drives, Bernoulli disks float between the read/write heads, so there is no actual contact between the disk and the heads. But the disk itself is flexible and removable like a floppy disk. Because the disk is flexible, it is less susceptible than a hard disk to head crashes. Bernoulli disk drives, however, are not as fast as hard disk drives.

A Bernoulli disk drive is sometimes called a Bernoulli box.


beta test

A test for a computer product prior to commercial release. Beta testing is the last stage of testing, and normally involves sending the product to beta test sites outside the company for real-world exposure.


Bézier curve

Pronounced “bez-ee-ay,” curved lines defined by mathematical formulas. Nearly all draw programs support Bézier curves.

Named after the French mathematician Pierre Bézier, Bézier curves employ at least three points to define a curve. The two endpoints of the curve are called anchor points. The other points, which define the shape of the curve, are called handles, tangent points, or nodes. Attached to each handle are two control points. By moving the handles themselves, or the control points, you can modify the shape of the curve.


BFT

See Binary File Transfer.


Big Blue

A slang name for International Business Machines Corporation (IBM). Blue is IBM's corporate color.


binary

Pertaining to a number system that has just two unique digits. For most purposes, we use the decimal number system, which has ten unique digits, 0 through 9. All other numbers are then formed by combining these ten digits. Computers are based on the binary numbering system, which consists of just two unique numbers, 0 and 1. All operations that are possible in the decimal system (addition, subtraction, multiplication, division) are equally possible in the binary system.

We use the decimal system in everyday life because it seems more natural (we have ten fingers and ten toes). For the computer, the binary system is more natural because of its electrical nature (charged versus uncharged).

In the decimal system, each digit position represents a value of 10 to the position's power. For example, the number 345 means:

3	three 100s (102)

plus

4	four 10s (101)

plus

5	five 1s (100)

In the binary system, each digit position represents a power of 2. For example, the binary number 1011 equals:

1	one 8 (23)

plus

0	zero 4s (22)

plus

1	one 2 (21)

plus

1	one 1 (20)

So a binary 1011 equals a decimal 11.

Because computers use the binary number system, powers of 2 play an important role. This is why everything in computers seems to come in 8s (23), 64s (26), 128s (27), and 256s (28).

Programmers also use the octal (8 numbers) and hexadecimal (16 numbers) number systems because they map nicely onto the binary system. Each octal digit represents exactly three binary digits, and each hexadecimal digit represents four binary digits.


binary compatible

Having the exact same data format, down to the binary level. That is, two files that are binary compatible will have the same pattern of zeroes and ones in the data portion of the file. The file header, however, may be different.

The term is used most commonly to state that data files produced by one application are exactly the same as data files produced by another application. For example, many software companies now produce applications for Windows and the Macintosh that are binary compatible, which means that a file produced in a Windows environment is interchangeable with a file produced on a Macintosh. This avoids many of the conversion problems caused by importing and exporting data.


binary file

A file stored in binary format. A binary file is computer-readable but not human-readable. All executable programs are stored in binary files, as are most numeric data files. In contrast, text files are stored in a form (usually ASCII) that is human-readable.


Binary File Transfer (BFT)

A standard for transmitting data files using fax modems. There are actually two standards, both of which are referred to as BFT: CCITT T.434 and Microsoft At Work (MAW).


binary format

A format for representing data used by some applications. The other main formats for storing data are text formats (such as ASCII and EBCDIC), in which each character of data is assigned a specific code number.

Binary formats are used for executable programs and numeric data, whereas text formats are used for textual data. Many files contain a combination of binary and text formats. Such files are usually considered to be binary files even though they contain some data in a text format.


bind

To assign a value to a symbolic placeholder. During compilation, for example, the compiler assigns symbolic addresses to some variables and instructions. When the program is bound, or linked, the binder replaces the symbolic addresses with real machine addresses. The moment at which binding occurs is called bind time or link time.


binder

Same as linker.


BinHex

An encoding scheme that converts binary data into ASCII characters. Any file, whether it be a graphics file, a text file, or a binary executable file, can be converted to BinHex. This format is particularly valuable for transferring files from one platform to another because nearly all computers can handle ASCII files. In fact, many e-mail programs include a BinHex encoder and decoder for sending and receiving attachments. BinHex is an especially common format for Macintosh files.  Encoded files usually have an .HQX extension.

An alternative algorithm for converting binary files to ASCII is uuencode.


BIOS

Pronounced “bye-ose,” an acronym for basic input/output system. The BIOS is built-in software that determines what a computer can do without accessing programs from a disk. On PCs, the BIOS contains all the code required to control the keyboard, display screen, disk drives, serial communications, and a number of miscellaneous functions.

The BIOS is typically placed on a ROM chip that comes with the computer (it is often called a ROM BIOS). This ensures that the BIOS will always be available and will not be damaged by disk failures. It also makes it possible for a computer to boot itself. Because RAM is faster than ROM, though, many computer manufacturers design systems so that the BIOS is copied from ROM to RAM each time the computer is booted. This is known as shadowing.

Many modern PCs have a flash BIOS, which means that the BIOS has been recorded on a flash memory chip, which can be updated if necessary.

The PC BIOS is standardized, so all PCs are alike at this level (although there are different BIOS versions). Additional DOS functions are usually added through software modules. This means you can upgrade to a newer version of DOS without changing the BIOS.

PC BIOSes that can handle Plug-and-Play (PnP) devices are known as PnP BIOSes, or PnP-aware BIOSes. These BIOSes are always implemented with flash memory rather than ROM.


bit

Short for binary digit, the smallest unit of information on a machine. The term was first used in 1946 by John Tukey, a leading statistician and adviser to five presidents. A single bit can hold only one of two values: 0 or 1. More meaningful information is obtained by combining consecutive bits into larger units. For example, a byte is composed of 8 consecutive bits.

Computers are sometimes classified by the number of bits they can process at one time or by the number of bits they use to represent addresses. These two values are not always the same, which leads to confusion. For example, classifying a computer as a 32-bit machine might mean that its data registers are 32 bits wide or that it uses 32 bits to identify each address in memory. Whereas larger registers make a computer faster, using more bits for addresses enables a machine to support larger programs.

Graphics are also often described by the number of bits used to represent each dot. A 1-bit image is monochrome; an 8-bit image supports 256 colors or grayscales; and a 24- or 32-bit graphic supports true color.


bit block transfer

A transformation of a rectangular block of pixels. Typical transformations include changing the color or shade of all pixels or rotating the entire rectangle. Many modern graphics adapters include hardwired bit block transformations, which execute much faster than they do when executed by software routines.


bit map

A representation, consisting of rows and columns of dots, of a graphics image in computer memory.The value of each dot (whether it is filled in or not) is stored in one or more bits of data. For simple monochrome images, one bit is sufficient to represent each dot, but for colors and shades of gray, each dot requires more than one bit of data. The more bits used to represent a dot, the more colors and shades of gray that can be represented.

The density of the dots, known as the resolution, determines how sharply the image is represented. This is often expressed in dots per inch (dpi) or simply by the number of rows and columns, such as 640 by 480.

To display a bit-mapped image on a monitor or to print it on a printer, the computer translates the bit map into pixels (for display screens) or ink dots (for printers). Optical scanners and fax machines work by transforming text or pictures on paper into bit maps.

Bit-mapped graphics are often referred to as raster graphics. The other method for representing images is known as vector graphics or object-oriented graphics. With vector graphics, images are represented as mathematical formulas that define all the shapes in the image. Vector graphics are more flexible than bit-mapped graphics because they look the same even when you scale them to different sizes. In contrast, bit-mapped graphics become ragged when you shrink or enlarge them.

Fonts represented with vector graphics are called scalable fonts, outline fonts, or vector fonts. The best-known example of a vector font system is PostScript. Bit-mapped fonts, also called raster fonts, must be designed for a specific device and a specific size and resolution.


bit-mapped font

See under font.


bit-mapped graphics

Refers to hardware and software that represent graphics images as bit maps. The other method for representing images is known as vector graphics.


bitblt

Pronounced bit-blit, short for bit block transfer.


BITNET

Short for Because It’s Time Network, BITNET is one of the oldest and largest wide-area networks, used extensively by universities. A new version of BITNET, called BITNET-II, relies on the Internet network to transfer messages and files.


bits per second

See bps.


blank character

Also called a space character. A blank character is produced when you press the space bar.


bleed

(n) Text or graphics that extends all the way to the edge of the paper. Bleeds are used for graphical effect and for printed tabs. Most printers cannot print all the way to the edge of the paper, so the only way to produce a bleed is to print on paper larger than the final page size and then trim the paper.

(v) To run to the edge of the paper, thereby producing a bleed.


block

(n) (1) In word processing, a block is a group of characters that you have marked to perform some action on them. For example, to move a section of text, you must first block it. This is sometimes called a block move.

To specify a block of text, you press special function keys (or click with a mouse) at the beginning and end of the block. The function keys differ from one word processor to another. Word processors usually display blocks by highlighting them on the screen.

(2) In data management, a block is a group of records on a storage device. Blocks are manipulated as units. For example, disk drives often read and write data in 512-byte blocks.

(3) In communications, a block is a fixed-size chunk of data that is transferred together. For example, the Xmodem protocol transfers blocks of 128 bytes. In general, the larger the block size, the faster the data transfer rate.

(v) In word processing, to specify a section of text. See definition (1) above. Some applications call this selecting.


block graphics

Graphical images created in character mode.


BMP

The standard bit-mapped graphics format used in the Windows environment. By convention, graphics files in the BMP format end with a .BMP extension.


board

Short for printed circuit board or expansion board.


boilerplate

Text or graphics elements designed to be used over and over. For example, you could create a boilerplate for a fax message that contains all the standard fax information that doesn’t change, such as your name, address , and phone number. Then whenever you want to create a new fax, you need only insert the boilerplate rather than retyping the information.

A boilerplate is similar to a template, but whereas a template holds layout and style information, a boilerplate contains actual text or graphics. Many applications, however, combine the two concepts.


boldface

A font that is darker than the regular face. For example

normal font	boldface font

Most word processors allow you to mark text as boldface.


bomb

To fail. The term bomb usually refers to a program hanging or ending prematurely. Note that bombing is usually less serious than crashing, because bombing refers to a single program, whereas crashing refers to the entire system. The two terms, however, are not always used consistently.

The Apple Macintosh computer actually has a bomb message that sometimes appears just before the system crashes.


Boolean expression

An expression that results in a value of either TRUE or FALSE. For example, the expression

2 < 5 (2 is less than 5)

is a Boolean expression because the result is TRUE. All expressions that contain relational operators, such as the less than sign (<), are Boolean. The operators—AND, OR, XOR, NOR, and NOT—are Boolean operators.

Boolean expressions are also called comparison expressions, conditional expressions, and relational expressions.


Boolean logic

Named after the nineteenth-century mathematician George Boole, Boolean logic is a form of algebra in which all values are reduced to either TRUE or FALSE. Boolean logic is especially important for computer science because it fits nicely with the binary  numbering system, in which each bit has a value of either 1 or 0. Another way of looking at it is that each bit has a value of either TRUE or FALSE.


Boolean operator

There are five Boolean operators that can be used to manipulate TRUE/FALSE values. These operators have the following meanings, where x and y represent values of TRUE or FALSE.

The OR operator is often called an inclusive OR, whereas XOR is an exclusive OR.

Boolean operators are used widely in programming and also in forming database queries. For example, the query

SELECT ALL WHERE LAST_NAME = “Smith” AND FIRST_NAME = “John”

finds all records with the name John Smith. But the query

SELECT ALL WHERE LAST_NAME = “Smith” OR FIRST_NAME = “John”

finds all records with the last name “Smith” or the first name “John.”


boot

(v) To load the first piece of software that starts a computer. Because the operating system is essential for running all other programs, it is usually the first piece of software loaded during the boot process.

Boot is short for bootstrap, which in olden days was a strap attached to the top of your boot that you could pull to help get your boot on. Hence, the expression “pull oneself up by the bootstraps.” Similarly, bootstrap utilities help the computer get started.

(n) Short for bootstrap, the starting-up of a computer, which involves loading the operating system and other basic software. A cold boot is when you turn the computer on from an off position. A warm boot is when you reset a computer that is already on.


box

(1) In graphical user interfaces, a box is an enclosed area, resembling a window, on the screen. Unlike windows, however, you generally cannot move or resize boxes.

There are many different types of boxes. For example, dialog boxes are boxes that request some type of information from you. Alert boxes are boxes that suddenly appear on the screen to give you information. Boxes can also be small rectangular icons that control windows. Zoom boxes, for example, enable you to make a window larger or smaller.

(2) Slang for personal computer or workstation.


bps

Abbreviation of bits per second, the standard measure of data transmission speeds. Standard telephone lines are capable of transmitting data at a maximum speed of about 14,400 bps. However, the old metal telephone wires are steadily being replaced by fiber optic cables, which are capable of transmitting data at much faster rates. Specialized cables for transmitting data between devices support rates of over 500,000 bps.

A number of standards define the format for sending data at various rates.


branch

In tree structures, a branch is a single line of the tree that ends with a leaf. The Windows File Manager, for example, has an Expand Branch command that shows all sub-directories of a specified directory.


Break key

A special key on computer keyboards that temporarily interrupts the computer's communications line. This usually terminates an established modem connection. Not all keyboards have a Break key, and not all programs respond to it. In DOS and Windows, you can abort the current  application and reboot the program by pressing the Break key in combination with the Control and Alt keys.


broadband ISDN (B-ISDN)

A standard for transmitting voice, video and data at the same time over fiber optic telephone lines. Broadband ISDN can support data rates of 1.5 million bits per second (bps), but it has not been widely implemented.


broadband transmission

A type of data transmission in which a single medium (wire) can carry several channels at once. Cable TV, for example, uses broadband transmission. In contrast, baseband transmission allows only one signal at a time.

Most communications between computers, including the majority of local-area networks, use baseband communications. An exception is B-ISDN networks, which employ broadband transmission.


broadcast

To simultaneously send the same message to more than one receiver. Broadcasting is a useful feature in e-mail systems. It is also supported by some fax systems.


browse

(1) In database systems, browse means to view data. Many database systems support a special browse mode, in which you can flip through fields and records quickly. Usually, you cannot modify data while you are in browse mode.

(1) 	In object-oriented programming languages, browse means to examine data structures.

(1) 	To view formatted documents. For example, you look at Web pages with a Web browser.


browser

Short for Web browser, a software application used to locate and display Web pages. Three of the most popular browsers are Netscape Navigator, Microsoft Internet Explorer, and Spyglass Mosaic. All of these are graphical browsers, which means that they can display graphics as well as text. In addition, most modern browsers can present multimedia information, including sound and video.


buffer

(n) A temporary storage area, usually in RAM. The purpose of most buffers is to act as a holding area, enabling the CPU to manipulate data before transferring it to a device.

Because the processes of reading and writing data to a disk are relatively slow, many programs keep track of data changes in a buffer and then copy the buffer to a disk. For example, word processors employ a buffer to keep track of changes to files. Then when you save the file, the word processor updates the disk file with the contents of the buffer. This is much more efficient than accessing the file on the disk each time you make a change to the file.

Note that because your changes are initially stored in a buffer, not on the disk, all of them will be lost if the computer fails during an editing session. For this reason, it is a good idea to save your file periodically. Most word processors automatically save files at regular intervals.

Another common use of buffers is for printing documents. When you enter a PRINT command, the operating system copies your document to a print buffer (a free area in memory or on a disk) from which the printer can draw characters at its own pace. This frees the computer to perform other tasks while the printer is running in the background. Print buffering is called spooling.

Most keyboard drivers also contain a buffer so that you can edit typing mistakes before sending your command to a program. Many operating systems, including DOS, also use a disk buffer to temporarily hold data that they have read from a disk. The disk buffer is really a cache.

(v) To move data into a temporary storage area.


bug

An error or defect in software or hardware that causes a program to malfunction. According to the folklore, the term originated when a moth trapped in the electrical workings of the first digital computer, the ENIAC, was discovered by Lieutenant Grace Hopper.


built-in font

Same as resident font.


built-in function

A function that is built into an application and can be accessed by end-users. For example, most spreadsheet applications support a built-in SUM function that adds up all cells in a row or column.


bullet

A small graphical element used to highlight or itemize a list:

A round bullet.

A square bullet.

A diamond bullet.

A pointing-finger bullet.


bulletin board system (BBS)

An electronic message center. Most bulletin boards serve specific interest groups. They allow you to dial in with a modem, review messages left by others, and leave your own message if you want. Bulletin boards are a particularly good place to find free or inexpensive software products. In the United States alone, there are tens of thousands of BBSs.


bundled software

Software that is sold with a computer or other hardware component as part of a package. As competition between computer manufacturers has intensified, bundling software has become a key strategy for attracting consumers. In some cases, the bundled software is even more valuable than the hardware.


bus

(1) A collection of wires through which data is transmitted from one part of a computer to another. You can think of a bus as a highway on which data travels within a computer. When used in reference to personal computers, the term bus usually refers to the expansion bus. This is a bus that connects all the various computer components—expansion boards and external devices such as disk drives and printers—to the CPU. Personal computers also have an address bus and data bus that connect the CPU with RAM.

The size of a bus, known as its width, is important because it determines how much data can be transmitted at one time. For example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus can transmit 32 bits of data.

Every bus has a clock speed measured in MHz. A fast bus allows data to be transferred faster, which makes applications run faster. On PCs, the old ISA bus is being replaced by faster buses such as PCI and EISA.

Many PCs made today include a local bus for data that requires especially fast transfer speeds, such as video data. The local bus is a high-speed pathway that connects directly to the processor.

Several different types of buses are used on Apple Macintosh computers. The fastest and most sophisticated is called the NuBus expansion bus.

(2) In networking, a bus is a central cable that connects all devices on a local-area network (LAN). It is also called the backbone.


bus mouse

A mouse that connects to a computer via an expansion board. Another type of mouse is a serial mouse, which connects to a serial port. Serial mice are easier to install, but the advantage of bus mice is that they do not use up the serial port, so you can use the port for a different device (a modem, for example).


bus topology

See under topology.


business graphics

See under presentation graphics.


button

(1) In graphical user interfaces, a button is a small outlined area in a dialog box that you can click to select an option or command.

(2) A mouse button is a button on a mouse that you click to perform various functions, such as selecting an object.


byte

Abbreviation for binary term, a unit of storage capable of holding a single character. On almost all modern computers, a byte is equal to 8 bits. Large amounts of memory are indicated in terms of kilobytes (1,024 bytes), megabytes (1,048,576 bytes), and gigabytes (approximately 1 billion bytes). A disk that can hold 1.44 megabytes, for example, is capable of storing approximately 1.4 million characters, or about 3,000 pages of information.


C

A high-level programming language developed by Dennis Ritchie and Brian Kernighan at Bell Labs in the mid 1970s. Although originally designed as a systems programming language, C has proved to be a powerful and flexible language that can be used for a variety of applications, from business programs to engineering. C is a particularly popular language for personal computer programmers because it is relatively small—it requires less memory than other languages.

The first major program written in C was the UNIX operating system, and for many years C was considered to be inextricably linked with UNIX. Now, however, C is an important language independent of UNIX.

Although it is a high-level language, C is much closer to assembly language than are most other high-level languages. This closeness to the underlying machine language allows C programmers to write very efficient code. The low-level nature of C, however, can make the language difficult to use for some types of applications.


C++

A high-level programming language developed by Bjarne Stroustrup at Bell Labs. C++ adds object-oriented features to its predecessor, C. C++ is rapidly becoming the programming language of choice for graphical applications, such as those that run in Windows and Macintosh environments.


cache

Pronounced cash, a special high-speed storage mechanism. It can be either a reserved section of main memory or an independent high-speed storage device. Two types of caching are commonly used in personal computers: memory caching and disk caching.

A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used for main memory. Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM.

Some memory caches are built into the architecture of microprocessors. The Intel 80486 microprocessor, for example, contains an 8K memory cache, and the Pentium has a 16K cache. Such internal caches are often called primary caches or Level 1 (L1) caches. You can also add additional external cache memory, sometimes called secondary or Level 2 (L2) caches.

Disk caching works under the same principle as memory caching, but instead of using high-speed SRAM, a disk cache uses conventional main memory. The most recently accessed data from the disk (as well as adjacent sectors) is stored in a memory buffer. When a program needs to access data from the disk, it first checks the disk cache to see if the data is there. Disk caching can dramatically improve the performance of applications, because accessing a byte of data in RAM can be thousands of times faster than accessing a byte on a hard disk.

When data is found in the cache, it is called a cache hit, and the effectiveness of a cache is judged by its hit rate. Many cache systems use a technique known as smart caching, in which the system can recognize certain types of frequently used data. The strategies for determining which information should be kept in the cache constitute some of the more interesting problems in computer science.


cache memory

See under cache.


CAD

Acronym for computer-aided design. A CAD system is a combination of hardware and software that enables engineers and architects to design everything from furniture to airplanes. In addition to the software, CAD systems require a high-quality graphics monitor; a mouse, light pen, or digitizing tablet for drawing; and a special printer or plotter for printing design specifications.

CAD systems allow an engineer to view a design from any angle with the push of a button and to zoom in or out for close-ups and long-distance views. In addition, the computer keeps track of design dependencies so that when the engineer changes one value, all other values that depend on it are automatically changed accordingly.

Until the mid 1980s, all CAD systems were specially constructed computers. Now, you can buy CAD software that runs on general-purpose workstations and powerful personal computers.


CAD/CAM

Acronym for computer-aided design/computer-aided manufacturing, computer systems used to design and manufacture products. The term CAD/CAM implies that an engineer can use the system both for designing a product and for controlling manufacturing processes. For example, once a design has been produced with the CAD component, the design itself can control the machines that construct the part.


CADD

Acronym for computer-aided design and drafting. CADD systems are CAD systems with additional drafting features. For example, CADD systems enable an engineer or architect to insert size annotations and other notes into a design.


CAE

Abbreviation of computer-aided engineering, computer systems that analyze engineering designs. Most CAD systems have a CAE component, but there are also independent CAE systems that can analyze designs produced by various CAD systems. CAE systems are able to simulate a design under a variety of conditions to see if it actually works.


calculator

(1) A small hand-held computer that performs mathematical calculations. Some calculators even permit simple text editing and programming.

(2) A program on a computer that simulates a hand-held calculator. Calculator programs let you perform simple math calculations without leaving the computer. The Apple Macintosh comes with a calculator desk accessory. Likewise, Microsoft Windows includes a calculator accessory.


calendar

A program that enables you to record events and appointments on an electronic calendar. Computer calendars act like datebooks, but they have several advantages over traditional datebooks:

automatic entries for regular events: You can specify, for example, that the first Thursday of every month is bridge night, and the calendar program will automatically fill in the appropriate days.

signaling of upcoming events: Most calendars will let you know that an event is approaching by issuing beeps.

clean deletion: With an electronic calendar, you can erase an appointment without leaving a trace.

Calendar software is part of a more general category of software known as PIMs (personal information managers). A special type of calendar, called a scheduler, enables groups of users connected to a network to coordinate their schedules.


call

(v) To invoke a routine in a programming language. Calling a routine consists of specifying the routine name and, optionally, parameters. For example, the following is a function call in the C programming language

printf(“Hello”)

The name of the function is printf and the parameter is “Hello.” This function call causes the computer to display the word Hello on the display screen.

A routine that invokes another routine is sometimes referred to as the calling routine. The routine that is invoked is referred to as the called routine.

 (n) An invocation of a routine.


CAM

Acronym for computer-aided manufacturing, a type of computer application that helps automate a factory. For example, the following are types of CAM systems

•	real-time control

•	robotics

•	materials requirements

All these systems are concerned with automatically directing the manufacture and inventory of parts.


camera-ready

In desktop publishing, camera-ready refers to the final state of a publication before it is printed. Historically, the term has meant that the copy is ready to be photographed and turned into plates for offset printing. Increasingly, however, it is possible to print directly from the electronic version, either by sending it to a high-resolution laser printer or to a special device that can generate plates directly from electronic elements rather than from photographs. In these cases, therefore, camera-ready means merely that the document is ready to be printed.


caps

Short for capital letters. For example, “all caps” means all letters capitalized.


Caps Lock key

A toggle key on computer keyboards that, when activated, causes all subsequent alphabetic characters to be uppercase, but has no effect on other keys.


capture

To save a particular state of a program. The term capture often refers to saving the information currently displayed on a display screen. You can capture the screen to a printer or to a file. The act of saving a display screen is called a screen capture.

The term capture is also used to describe the recording of keystrokes during the definition of a macro.


card

(1) Same as printed circuit board.

(2) In hypertext systems such as HyperCard, a card is a single page of information.


caret

A wedge-shaped symbol (^) generally found above the 6 on computer keyboards. In older technical documentation, the caret is often used to indicate the Control key. For example, “^C” would mean press the “C” key while holding down the Control key. Most modern documentation, however, would specify this key sequence as Ctrl+C.

The caret symbol is also called a hat.


carpal tunnel syndrome

A common form of Repetitive Strain Injury (RSI) produced by repeating the same small movements many times. As more and more people use computers, carpal tunnel syndrome and other forms of RSI have become more prevalent. Typical symptoms are numbness or burning in the fingers or wrist. If not addressed early on, the injury can cause permanent damage.

There are a number of ways to avoid carpal tunnel syndrome, including adjusting the height and angle of your chair and keyboard, and taking frequent breaks from typing. Modern office furniture, designed especially for computer use, can help considerably.


carriage

The mechanism on a printer that feeds paper. A wide-carriage printer is a printer that can accept very wide paper. A narrow-carriage printer is a printer that accepts only standard-sized paper.


carriage return

Often abbreviated CR, a carriage return is a special code that moves the cursor (or print head) to the beginning of the current  line. In the ASCII character set, a carriage return has a decimal value of 13.


cartridge

(1) A removable storage medium (tape, disk, or memory chip). Some printers have slots in which you can insert cartridges to load different fonts. A font loaded from a cartridge is called a font cartridge or cartridge font.

The term removable cartridge usually refers to a type of hard disk that you can remove. Removable cartridges offer the speed of hard disks along with the portability of floppy disks.

(2) For laser printers, a toner cartridge is a metal container that holds the toner.


cartridge font

Same as font cartridge.


cascading windows

An arrangement of windows such that they overlap one another. Typically, the title bar remains visible so that you can always see which windows are open. Cascading windows are also called overlaid windows. An alternative arrangement of windows, in which every window is completely visible, is called tiled windows.


case sensitive

A program's ability to distinguish between uppercase (capital) and lowercase (small) letters. Programs that distinguish between uppercase and lowercase are said to be case sensitive.

A case-sensitive program that expects you to enter all commands in uppercase will not respond correctly if you enter one or more characters in lowercase. It will treat the command RUN differently from run. Programs that do not distinguish between uppercase and lowercase are said to be case insensitive.


cathode ray tube

See CRT.


CBT

Acronym for computer-based training, a type of education in which the student learns by executing special training programs on a computer. CBT is especially effective for training people to use computer applications because the CBT program can be integrated with the applications so that students can practice using the application as they learn.

Historically, CBTs growth has been hampered by the enormous resources required: human resources to create a CBT program. and hardware resources needed to run it. However, the increase in PC computing power, and especially the growing prevalence of computers equipped with CD-ROMs, is making CBT a more viable option for corporations and individuals alike. Many PC applications now come with some modest form of CBT, often called a tutorial.


CCD

Short for charge-coupled device, an instrument whose semiconductors are connected so that the output of one serves as the input of the next. Digital cameras, video cameras, and optical scanners all use CCD arrays.


CCITT

Abbreviation of Comité Consultatif International Téléphonique et Télégraphique, an organization that sets international communications standards. CCITT has defined many important standards for data communications, including the following:

Group 3: The universal protocol for sending fax documents across telephone lines. The Group 3 protocol specifies CCITT T.4 data compression and a maximum transmission rate of 9,600 baud. There are two levels of resolution: 203 by 98 and 203 by 196.

Group 4: A protocol for sending fax documents over ISDN networks. The Group 400 protocol supports images of up to 400 dpi resolution.

V.21: The standard for full-duplex communication at 300 baud in Japan and Europe. In the United States, Bell 103 is used in place of V.21.

V.22: The standard for half-duplex communication at 1,200 bps in Japan and Europe. In the United States, the protocol defined by Bell 212A is more common.

V.22bis: The worldwide standard for full-duplex modems sending and receiving data across telephone lines at 1,200 or 2,400 bps.

V.29: The standard for half-duplex modems sending and receiving data across telephone lines at 1,200, 2,400, 4,800, or 9,600 bps. This is the protocol used by fax modems.

V.32: The standard for full-duplex modems sending and receiving data across phone lines at 4,800 or 9,600 bps. V.32 modems automatically adjust their transmission speeds based on the quality of the lines.

V.32bis: The V.32 protocol extended to speeds of 7,200, 12,000, and 14,400 bps.

V.34: The standard for full-duplex modems sending and receiving data across phone lines at up to 28,800 bps. V.34 modems automatically adjust their transmission speeds based on the quality of the lines.

V.42: An error-detection standard for high-speed modems. V.42 can be used with digital telephone networks. See MNP for a competing standard.

V.42bis: A data compression protocol that can enable modems to achieve a data transfer rate of 34,000 bps.

X.25: The most popular packet-switching protocol for LANs. Ethernet, for example, is based on the X.25 standard.

X.400: The universal protocol for e-mail. X.400 defines the envelope for e-mail messages so all messages conform to a standard format.

X.500: An extension to X.400 that defines addressing formats so all e-mail systems can be linked together.


CD-I (Compact Disc-Interactive)

A software and hardware standard developed by Philips International for storing video, audio, and binary  data on compact optical disks. It supports 552MB (megabytes) of binary  data and specifies several different types of video and audio encoding formats. Unlike conventional CD-ROM drives, CD-I drives have a built-in microprocessor to handle many of the computing functions. It is sometimes referred to as the Green Book standard.

A competing standard, developed by Intel Corporation, is known as DVI (Digital Video Interactive).


CD-R drive

Short for Compact Disk-Recordable drive, a type of disk drive that can create CD-ROMs. This allows users to “master” a CD-ROM for publishing. Until recently, CD-R drives were quite expensive, but prices have dropped dramatically.

CD-R drives can also read CD-ROMs.


CD-recordable drive

See CD-R drive.


CD-ROM

Pronounced see-dee-rom, abbreviation of Compact Disc-Read-Only Memory. A type of optical disk capable of storing large amounts of data—up to 1GB, although the most common size is 630MB (megabytes). A single CD-ROM has the storage capacity of 700 floppy disks, enough memory to store about 300,000 text pages.

CD-ROMs require a special machine to record the data, and once recorded, they cannot be erased and filled with new data. To read a CD, you need a CD-ROM player. Almost all CD-ROMs conform to a standard size and format, so it is usually possible to load any type of CD into any ROM player. In addition, most CD-ROM players are capable of playing audio CDs, which share the same technology.

CD-ROMs are particularly well-suited to information that requires large storage capacity. This includes color graphics, sound, and especially video. In recent years, as the prices of CD-ROM players have decreased, and the tools for creating new CD-ROM titles have improved, the CD-ROM industry has been expanding rapidly. To date, the most popular CD-ROM titles have been computer games and multimedia reference works.


CD-ROM drive

Same as CD-ROM player.


CD-ROM player

Also called a CD-ROM drive, a CD-ROM player is a device that can read information from a CD-ROM. CD-ROM players can be either internal, in which case they fit in a bay, or external, in which case they generally connect to the computer’s parallel port. Parallel CD-ROM players are easier to install, but they have several disadvantages: They’re somewhat more expensive than internal players, they use up the parallel port which means that you can’t use that port for another device such as a printer, and the parallel port itself may not be fast enough to handle all the data pouring through it.

There are a number of features that distinguish CD-ROM players, the most important of which is probably their speed. CD-ROM players are generally classified as single-speed, double-speed (2X), triple-speed (3X), quadruple-speed (4X), or six-times speed (6X). Within these groups, however, there is some variation. Two more precise measurements are the drive’s seek time and data transfer rate. The seek time, also called the access time, measures how long, on average, it takes the drive to access a particular piece of information. The data transfer rate measures how much data can be read and sent to the computer in a second.

Aside from its speed, another important feature of a CD-ROM player is its compatibility with existing standards. If you plan to run CD-ROMs in a windows environment, you need a player that conforms to the MPC II standard. If you want to be able to view photographs stored on CD-ROM, make sure your player conforms to Kodak’s PhotoCD format.

Finally, you should consider how the player connects to your computer. Most CD-ROMs connect via a SCSI bus. If your computer doesn’t already contain such an interface, you will need to install one. Other CD-ROMs connect to an IDE or Enhanced IDE interface, which is the one used by the hard disk drive; still others use a proprietary interface.


cdev

Short for control panel device, and pronounced see-dev, a cdev is a special type of Macintosh utility that enables you to adjust basic system parameters. On newer Macs (System 7 and later) cdevs are called control panels.


cell

In spreadsheet applications, a cell is a box in which you can enter a single piece of data. The data is usually text, a numeric value, or a formula. The entire spreadsheet is composed of rows and columns of cells. A spreadsheet cell is analogous to a field in database management systems.

Individual cells are usually identified by a column letter and a row number. For example, D12 specifies the cell in column D and row 12.


central processing unit

See CPU.


Centronics interface

A standard interface for connecting printers and other parallel devices. Although Centronics Corporation designed the original standard, the Centronics interface used by modern computers was designed by Epson Corporation. For PCs, almost all parallel ports conform to the Centronics standard. Two new parallel port standards that are backward compatible with Centronics, but offer faster transmission rates, are ECP (Extend Capabilities Port)  and EPP (Enhanced Parallel Port) .


CGA

Abbreviation of color/graphics adapter, an old graphics system for PCs. Introduced in 1981 by IBM, CGA was the first color graphics system for IBM PCs. Designed primarily for computer games, CGA does not produce sharp enough characters for extended editing sessions. CGA's highest-resolution mode is 2 colors at a resolution of 640 by 200.

CGA has been superseded by VGA systems, which are backward compatible with CGA.


CGI

Abbreviation of Common Gateway Interface, CGI is a specification for transferring information between a World Wide Web server and a CGI program. A CGI program is any program designed to accept and return data that conforms to the CGI specification. The program could be written in any  programming language, including C , Perl, or Visual Basic.

CGI programs are the most common way the Web servers to interact dynamically with users. Many HTML pages that contain forms, for example, use a CGI program to process the form’s data once it’s submitted. Another increasingly common way to provide dynamic feedback for Web users is to include scripts or programs that run on the user’s machine rather than the Web server. These programs can be Java applets, Java scripts, or ActiveX components. These technologies are known collectively as client-side solutions, while the use of CGI is a server-side solution because the processing occurs on the Web server.


CGM

Abbreviation of Computer Graphics Metafile, a file format designed by several standards organizations and formally ratified by ANSI. It is designed to be the standard vector graphics file format and is supported by a wide variety of software and hardware products.


channel

(1) In communications, the term channel refers to a communications path between two computers or devices. It can refer to the physical medium (the wires) or to a set of properties that distinguishes one channel from another. For example, TV channels refer to particular frequencies at which radio waves are transmitted.

(2) For IBM PS/2 computers, a channel is the same as an expansion bus.


character

In computer software, any symbol that requires one byte of storage. This includes all the ASCII and extended ASCII characters, including the space character. In character-based software, everything that appears on the screen, including graphics symbols, is considered to be a character. In graphics-based applications, the term character is generally reserved for letters, numbers, and punctuation.


character based

Describes programs capable of displaying only ASCII (and extended ASCII) characters. Character-based programs treat a display screen as an array of boxes, each of which can hold one character. When in text mode, for example, PC screens are typically divided into 25 rows and 80 columns. In contrast, graphics-based programs treat the display screen as an array of millions of pixels. Characters and other objects are formed by illuminating patterns of pixels.

Because the IBM extended ASCII character set includes shapes for drawing pictures, character-based programs are capable of simulating some graphics objects. For example, character-based programs can display windows and menus, bar charts, and other shapes that consist primarily of straight lines. However, they cannot represent more complicated objects that contain curves.

Unlike PCs, the Macintosh computer is a graphics-based machine. All programs that run on a Macintosh computer are graphics based.


character mode

Many video adapters support several different modes of resolution. All such modes are divided into two general categories: character mode (also called text mode) and graphics mode. In character mode, the display screen is treated as an array of blocks, each of which can hold one ASCII character. In graphics mode, the display screen is treated as an array of pixels, with characters and other shapes formed by turning on combinations of pixels.

Of the two modes, character mode is much simpler. Programs that run in character mode generally run much faster than those that run in graphics mode, but they are limited in the variety of fonts and shapes they can display. Programs that run entirely in character mode are called character-based programs.


character recognition

See optical character recognition.


character set

A defined list of characters recognized by the computer hardware and software. Each character is represented by a number. The ASCII character set, for example, uses the numbers 0 through 127 to represent all English characters as well as special control characters. European ISO character sets are similar to ASCII, but they contain additional characters for European languages.


character string

A series of characters manipulated as a group. A character string differs from a name in that it does not represent anything—a name stands for some other object.

A character string is often specified by enclosing the characters in single or double quotes. For example, WASHINGTON would be a name, but 'WASHINGTON' and “WASHINGTON” would be character strings.

The length of a character string is usually the number of characters in it. For example, the character string “WASHINGTON” has a length of 10 (the quote marks are not included). Some programs, however, mark the beginning or end of a character string with an invisible character, so the length might actually be one greater than the number of characters.


characters per second

See cps.


charge-coupled device

See under CCD.


chassis

A metal frame that serves as the structural support for electronic components. Every computer system requires at least one chassis to house the circuit boards and wiring. The chassis also contains slots for expansion boards. If you want to insert more boards than there are slots, you will need an expansion chassis, which provides additional slots.

There are two basic flavors of chassis designs–desktop models and tower models–but there are many variations on these two basic types.


chat

Real-time communication between two users via computer. Once a chat has been initiated, either user can enter text by typing on the keyboard and the entered text will appear on the other user’s monitor. Most networks and online services offer a chat feature, but it is not widely used because it is easier to communicate by telephone, and messages that aren’t urgent can be sent by e-mail.


check box

In graphical user interfaces, a box that you can click to turn an option on or off. When the option is on, an X appears in the box. [picture of check boxes]


checksum

A simple error-detection scheme in which each transmitted message is accompanied by a numerical value based on the number of set bits in the message. The receiving station then applies the same formula to the message and checks to make sure the accompanying numerical value is the same. If not, the receiver knows that the message has been garbled.


Chicago

See under Windows 95.


chip

A small piece of semiconducting material (usually silicon) on which an integrated circuit is embedded. A typical chip is less than ¼-square inches and can contain millions of electronic components (transistors). Computers consist of many chips placed on electronic boards called printed circuit boards.

There are different types of chips. For example, CPU chips (also called microprocessors) contain an entire processing unit, whereas memory chips contain blank memory.

Chips come in a variety of packages. The three most common are:

DIPs: Dual in-line packages are the traditional buglike chips that have anywhere from 8 to 40 legs, evenly divided in two rows.

PGAs: Pin-grid arrays are square chips in which the pins are arranged in concentric squares.

SIPs: Single in-line packages are chips that have just one row of legs in a straight line like a comb.

In addition to these types of chips, there are also single in-line memory modules (SIMMs), which consist of up to nine chips packaged as a single unit.


choose

To pick a command or option. To choose a menu command or command button in a graphical user interface, you click on it. The terms choose and select are often used interchangeably, but some authors make a distinction between choosing, which actually activates a command, and selecting, which merely highlights a command or other object.


Chooser

A Macintosh desk accessory (DA) that enables you to select and configure printers and network devices, such as file servers.


CIE color model

A color model based on human perception developed by the CIE (Commission Internationale de l’Eclairage) committee. While widely regarded as the most accurate color model, CIE is unsuitable for many technologies, including color printing and color monitors. Consequently, these systems need to use other color models, such as CMYK and RGB. There is a growing trend, however, to make all color models relative to the CIE model. This would make it easier to translate from one model to another.


Cinepak

A popular codec (compression/decompression technology) for computer video developed by SuperMac Inc.


circuit board

Short for printed circuit board.


CIS

Short for CompuServe Information Service. See under CompuServe.


CISC

Pronounced sisk, and stands for complex instruction set computer. Most personal computers, use a CISC architecture, in which the CPU supports as many as two hundred instructions. An alternative architecture, used by many workstations and also some personal computers, is RISC (reduced instruction set computer) , which supports fewer instructions.


class

In object-oriented programming, a category of objects. For example, there might be a class called shape that contains objects which are circles, rectangles, and triangles. The class defines all the common properties of the different objects that belong to it.


clear

To erase. Clear the screen, for example, means to erase everything on the display screen. Clear a variable means to remove whatever data is currently stored in the variable. Clear memory means to erase all data currently stored in memory.


click

(v) To tap on a mouse button, pressing it down and then immediately releasing it. Note that clicking a mouse button is different from pressing (or dragging) a mouse button, which implies that you hold the button down without releasing it. The phrase to click on means to select (a screen object) by moving the mouse pointer to the object's position and clicking a mouse button.

Some operations require a double click, meaning that you must click a mouse button twice in rapid succession. Shift clicking refers to clicking the mouse button while holding the Shift key down.

(n) The pressing down and rapid release of a mouse button.


client/server architecture

A network architecture in which each computer or process on the network is either a client or a server. Servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers). Clients are less powerful PCs or workstations on which users run applications. Clients rely on servers for resources, such as files, devices, and even processing power.

Another type of network architecture is known as a peer-to-peer architecture because each node has equivalent responsibilities. Both client/server and peer-to-peer architectures are widely used, and each has unique advantages and disadvantages.


clip

In computer graphics, to cut off a portion of a graphic at a defined boundary. Most bit-mapped graphics utilities provide a clip feature than enables you to draw a window around an object and clip everything outside of the window.


clip art

Electronic illustrations that can be inserted into a document. Many clip-art packages are available, some general and others specialized for a particular field. Most clip-art packages provide the illustrations in several file formats so that you can insert them into various word-processing systems.


clipboard

A special file or memory area (buffer) where data is stored temporarily before being copied to another location. Many word processors, for example, use a clipboard for cutting and pasting. When you cut  a block of text, the word processor copies the block to the clipboard; when you paste the block, the word processor copies it from the clipboard to its final destination. In Microsoft Windows and the Apple Macintosh operating system, the Clipboard (with a capital C) can be used to copy data from one application to another.

The Macintosh uses two types of clipboards. The one it calls the Clipboard can hold only one item at a time and is flushed when you turn the computer off. The other, called the Scrapbook, can hold several items at once and retains its contents from one working session to another.


clock rate

Same as clock speed.


clock speed

Also called clock rate, the speed at which a microprocessor executes instructions. Every computer contains an internal clock that regulates the rate at which instructions are executed and synchronizes all the various computer components. The CPU requires a fixed number of clock ticks (or clock cycles) to execute each instruction. For example, an Intel 80286 microprocessor needs about 20 clock cycles to multiply two numbers together. The faster the clock, the more instructions the CPU can execute per second.

Clock speeds are expressed in megahertz (MHz), 1MHz being equal to 1 million cycles per second. Personal computers have clock speeds of anywhere from 4MHz to over 100MHz.

Usually, the clock rate is a fixed characteristic of the microprocessor. Some computers, however, have a switch that lets you choose between two or more different clock speeds. This is useful because programs written to run on a machine with a high clock rate may not work properly on a machine with a slower clock rate, and vice versa. In addition, some add-on components may not be able to run at high clock speeds.

The internal architecture of a CPU has as much to do with a CPU’s performance as the clock speed, so two CPUs with the same clock speed will not necessarily perform equally. Whereas an Intel 80286 microprocessor requires 20 cycles to multiply two numbers, an Intel 80486 or later processor can perform the same calculation in a single clock tick. These newer processors, therefore, would be 20 times faster than the older processors even if their clock speeds were the same.

Like CPUs, expansion buses  also have clock speeds. Ideally, the CPU clock speed and the bus clock speed should be the same so that neither component slows down the other. In practice, the bus clock speed is often slower than the CPU clock speed.


clone

A computer, software product, or device that functions exactly like another, better-known product. For example, IBM PC clones are personal computers that offer the same functionality as an IBM PC but are produced by other companies. If the clone is good, you should be unable to tell the difference between it and the real product.

The term clone implies that the product is an exact duplicate. Note that the term clone is a bit stronger than the term compatible. For example, an IBM PC clone is a computer that has most, if not all, the same components as a real IBM PC. The term IBM-compatible, on the other hand, implies only that the computer is capable of running any program that an IBM PC can run. This does not mean that it is the same internally.


close

(1) To finish work on a data file and save it.

(2) In graphical user interfaces, to close a window means to exit an application or file, thereby removing the window from the screen.


cluster

A group of disk sectors. The operating system assigns a unique number to each cluster and then keeps track of files according to which clusters they use. Occasionally, the operating system marks a cluster as being used even though the file that is supposedly using it no longer exists. This is called a lost cluster. You can free up disk space by deleting lost clusters, but you should first make sure that the clusters do not, in fact, contain valuable data.


CMOS

Abbreviation of complementary metal oxide semiconductor. Pronounced see-moss, CMOS is a widely used type of semiconductor. CMOS semiconductors require less power than NMOS transistors, making them particularly attractive for use in battery-powered devices, such as portable computers. Many personal computers contain a small amount of battery-powered CMOS memory to hold the date, time, and system setup parameters.


CMS

See color management system.


CMYK

Short for Cyan-Magenta-Yellow-Black, and pronounced as separate letters. CMYK is a color model in which all colors are described as a mixture of these four process colors. CMYK is the standard color model used in offset printing for full-color documents. Because such printing uses inks of these four basic colors, it is often called four-color printing.

In contrast, display devices generally use a different color model called RGB, which stands for Red-Green-Blue. One of the most difficult aspects of desktop publishing in color is color matching—properly converting the RGB colors into CMYK colors so that what gets printed looks the same as what appears on the monitor.


coaxial cable

A type of wire that consists of a center wire surrounded by insulation and then a grounded shield of braided wire. The shield minimizes electrical and radio frequency interference.

Coaxial cabling is the primary type of cabling used by the cable television industry and is also widely used for computer networks. Although more expensive than standard telephone wire, it is much less susceptible to interference and can carry much more data. Because the cable television industry has already connected millions of homes with coaxial cable, many analysts believe that they are the best positioned to capitalize on the much-heralded information highway.


COBOL

Acronym for common business oriented language. Developed in the late 1950s and early 1960s, COBOL is the second-oldest high-level programming language (FORTRAN is the oldest). It is particularly popular for business applications that run on large computers.

COBOL is a wordy language; programs written in COBOL tend to be much longer than the same programs written in other languages. This can be annoying when you program in COBOL, but the wordiness makes it easy to understand programs because everything is spelled out. Although disparaged by many programmers for being outdated, COBOL is still the most widely used programming language in the world.


code

(n) (1) A set of symbols for representing something. For example, most computers use ASCII codes to represent characters.

(2) Written computer instructions. The term code is somewhat colloquial. For example, a programmer might say: “I wrote a lot of code this morning” or “There's one piece of code that doesn't work.”

Code can appear in a variety of forms. The code that a programmer writes is called source code. After it has been compiled, it is called object code. Code that is ready to run is called executable code or machine code.

(v) Colloquial for to program (that is, to write source code).


codec

Short for compressor/decompressor, a codec is any technology for compressing and decompressing data. Codecs can be implemented in software, hardware, or a combination of both. Some popular codecs for computer video include MPEG, Indeo, Cinepak, QuickTime, and Video for Windows.


cold boot

The start-up of a computer from a powered-down state.


collapse

To compress a view of a hierarchy so that only the roots of each branch are visible. The opposite of collapse is expand, which makes the entire branch visible.


color depth

The number of distinct colors that can be represented by a piece of hardware or software. Color depth is sometimes referred to as bit depth because it is directly related to the number of bits used for each pixel. An 16-bit video adapter, for example, has a color depth of 216 (about 16.7 million) colors.


color management system (CMS)

A system for ensuring that colors remain the same regardless of the device or medium used to display the colors. This is extremely difficult because different devices use different technologies and models to produce colors. In addition, color is highly subjective. The same colors look different to different people.


color matching

The process of assuring that a color on one medium remains the same when converted to another medium. This is extremely difficult because different media use different color models. Color monitors, for example, use the RGB model, whereas process printing uses the CMYK model. As color desktop publishing matures, color matching is gaining more and more attention. The most recent Windows and Macintosh operating systems include a color management system (CMS) to assist in color matching.


color monitor

A display monitor capable of displaying many colors. In contrast, a monochrome monitor can display only two colors—one for the background and one for the foreground. Color monitors implement the RGB color model by using three different phosphors that appear red, green, and blue when activated. By placing the phosphors directly next to each other, and activating them with different intensities, color monitors can create an unlimited number of colors. In practice, however, the real number of colors that any monitor can display is controlled by the video adapter.


color printer

A printer capable of printing more than one color. Most color printers are based on the CMYK color model, which prints in four basic colors: cyan, magenta, yellow, and black. By printing combinations of different colors close to each other (or, in the case of thermal dye transfer printers, on top of each other), the CMYK model can simulate most other colors (except for special colors such as fluorescent yellow). This is the same technique used in process color offset printing, which is the technology used to print most color books, magazines, and other paper materials. Some lower-price printers use only three colors—cyan, magenta, and yellow—but these printers cannot print true black and their colors tend to be a bit faded.

Color printers use a variety of techniques to lay down the different colors:

Thermal dye transfer printers, also called dye sublimation printers, heat ribbons containing dye and then diffuse the dyes onto specially coated paper or transparencies. These printers are the most expensive and slowest, but they produce continuous-tone images that mimic actual photographs. Note that you need special paper, which is quite expensive.

Thermal wax transfer printers use wax-based inks that are melted and then laid down on regular paper or transparencies. Unlike thermal dye transfer printers, these printers print images as dots, which means that images must be dithered first. As a result images are not quite photo-realistic, although they are very good. The big advantages of these printers over thermal dye transfer printers are that they don’t require special paper and they are faster.

Solid ink-jet printers, also called wax jet or phase change printers, work by melting dyed wax and then spraying it on paper. This produces bright colors on virtually any type of paper. The downside to solid ink-jet printers is that they are slow and relatively expensive.

Color laser printers use the same principle as monochrome laser printers, but they include four toners rather than one. Although laser printers produce better quality output than ink-jet printers, they are also three to four times more expensive.

Color ink-jet printers are the least expensive color printers. They contain three or four separate nozzles, each of which sprays a different color of ink.


color separation

The act of decomposing a color graphic or photo into single-color layers. For example, to print full-color photos with an offset printing press, one must first separate the photo into the four basic ink colors: cyan, magenta, yellow, and black (CMYK). Each single-color layer is then printed separately, one on top of the other, to give the impression of infinite colors.

This type of color separation, mixing three or four colors to produce an infinite variety of colors, is called process color separation. Another type of color separation, called spot color separation, is used to separate colors that are not to be mixed. In this case, each spot color is represented by its own ink, which is specially mixed. Spot colors are effective for highlighting text but they cannot be used to reproduce full-color images.

Traditionally, process color separation has been performed photographically with different colored filters. However, many modern desktop publishing systems are now capable of producing color separations for graphics stored electronically. This capability is essential if you want to create full-color documents on your computer and then print them using an offset printer. You don’t need to perform color separation if you are printing directly to a color printer because in this case the printer itself performs the color separation internally.


color/graphics adapter

See CGA.


column

(1) On a display screen in character mode, a column is a vertical line of characters extending from the top to the bottom of the screen. The size of a text display is usually measured in rows and columns.

(2) In spreadsheets, a column is a vertical row of cells. Spreadsheet columns are usually identified by letters.

(3) In database management systems, column is another name for field.

(4) In documents, a column is a vertical area reserved for text. Most newspapers, for example, contain four or more columns per page. Modern word processors and desktop publishing systems enable you to automatically divide a page into columns.


column graph

A type of presentation graphic in which numerical values are illustrated with horizontal columns. Column graphs are particularly effective for showing values that are categorized by two separate characteristics, such as year and sector.


COM

(1) In DOS systems, the name of a serial communications port. DOS supports four serial port names: COM1, COM2, COM3, and COM4, but most PCs have only two physical serial ports. This means that the names overlap. Typically, COM1 and COM3 refer to one port, while COM2 and COM4 refer to the other. So if you have two devices, one of which is attached to COM1 and the other to COM3, you cannot use them simultaneously.

(2) Abbreviation of Component Object Model.


COM file

In DOS environments, a COM file is an executable command file with a .COM filename extension. COM files can be directly executed and are usually slightly smaller than equivalent EXE files. However, COM files cannot exceed 64K, so large programs are usually stored in EXE files.


Comité Consultatif International Téléphonique et Télégraphique

See under CCITT.


comma-delimited

A data format in which each piece of data is separated by a comma.


command

An instruction to a computer or device to perform a specific task. Commands come in different forms. They can be:

•	special words (keywords) that a program understands.

•	function keys

•	choices in a menu

•	buttons or other graphical objects on your screen

Every program that interacts with people responds to a specific set of commands. The set of commands and the syntax for entering them is called the user interface and varies from one program to another.

The DOS operating system makes a distinction between internal and external commands. Internal commands are commands, such as COPY and DIR, that can be handled by the COMMAND.COM program. External commands include the names of all other COM files, as well as EXE and BAT files.

Another word for command is directive.


command buffer

A temporary storage area where commands are kept. (In DOS environments, the command buffer is called a template.) DOS and UNIX support several operations for manipulating the command buffer. For example, you can use the F3 function key in DOS to copy the template's contents to the display screen. This is useful for repeating a command or for correcting a mistake.

Command buffers also make it possible for programs to undo commands.


command driven

Refers to programs that accept commands in the form of special words or letters. In contrast, programs that allow you to choose from a list of options in a menu are said to be menu driven. Command-driven software is often more flexible than menu-driven software, but it is more difficult to learn.


Command key

Macintosh computers have a special command key marked by a four-leaf clover [picture] or an apple [picture]. The Command key is similar to a PC’s Alt key—you hold it down while pressing another key to execute some operation. Typically, command-key combinations are shorthands for menu choices. For example, on the desktop, pressing [picture]-O is equivalent to selecting the open option from the file menu.

The Command key is sometimes called the Apple key or Open Apple.


command language

The programming language through which a user communicates with the operating system or an application. For example, the DOS command language includes the commands DIR, COPY, and DEL, to name a few. The part of an operating system that responds to operating system commands is called the command processor.

With graphical user interfaces, the command language consists of operations you perform with a mouse or similar input device.


command line

The line on the display screen where a command is expected. Generally, the command line is the line that contains the most recently displayed command prompt.


command line interpreter

Same as command processor.


command processor

The part of the operating system that receives and executes operating system commands. Every operating system has a command processor. When the command prompt is displayed, the command processor is waiting for a command. After you enter a command, the command processor analyzes the syntax to make sure the command is valid, and then either executes the command or issues an error warning. For operating systems with a graphical user interface, the command processor interprets mouse operations and executes the appropriate command.

Another term for command processor is command line interpreter.


COMMAND.COM

The DOS file that contains all the DOS command processor.


Commodore Amiga

See Amiga.


common carrier

Same as public carrier.


Common Gateway Interface

See CGICGI.


communications

The transmission of data from one computer to another, or from one device to another. A communications device, therefore, is any machine that assists data transmission. For example, modems, cables, and ports are all communications devices. Communications software refers to programs that make it possible to transmit data.


communications protocol

All communications between devices require that the devices agree on the format of the data. The set of rules defining a format is called a protocol. At the very least, a communications protocol must define the following:

•	rate of transmission (in baud or bps)

•	whether transmission is to be synchronous or asynchronous

•	whether data is to be transmitted in half-duplex or full-duplex mode

In addition, protocols can include sophisticated techniques for detecting and recovering from transmission errors and for encoding and decoding data.

The table lists the most commonly used protocols for communications via modems. These protocols are almost always implemented in the hardware; that is, they are built into modems.

In addition to the standard protocols listed in the table, there are a number of protocols that complement these standards by adding additional functions such as file transfer capability, error detection and recovery, and data compression. The best-known are Xmodem, Kermit, MNP, and CCITT V.42. These protocols can be implemented either in hardware or software.


communications software

Software that makes it possible to send and receive data over telephone lines through modems. The following features differentiate various communications software packages:

maximum bps rate: The software package should be able to transmit data as fast as your modem. Maximum bps rates for communications packages vary between 9,600 and 57,600 bps.

automatic queue and redial: This is a useful feature if you use your modem to access a service that is frequently busy, such as a bulletin board system (BBS) . When you enter the telephone number in a queue, the communications software will keep redialing the number until it gets through. This feature can also be implemented by the modem itself rather than by the software.

macros: The ability to create macros is very important because you often go through the same steps every time you make a connection. By storing the connection sequence in a macro, you can perform the entire process with a single keystroke.

file transfer protocols: File transfer protocols enable you to transmit ASCII or binary files over a telephone line. The more protocols the package supports, the better. At the very least, it should support Xmodem and Kermit. For high-speed communication, you may require additional protocols, such as Zmodem.

script language: A script is like a program or batch file. It is a file of commands that can be executed without your interaction. The ability to write scripts is useful if you need to log on to services and transfer files while away from your computer.

remote: Packages that support a remote option enable your computer to accept calls while you are not there. This feature is also called auto-answer.

spooling: Packages that support spooling enable you to run another program while files are being transferred in the background. This is sometimes called background processing.

terminal emulation drivers: This is important if you plan to log on to a mainframe from your PC. Most mainframes require that the PC emulate a particular type of terminal. The more terminal emulation drivers a package has, the more mainframes you can log on to. Most packages support TTY emulation and emulate one or more DEC terminals (such as the VT52, VT100/102, or VT220).

In addition to these features, some communications packages offer more advanced programming capabilities that enable you to customize the interface using windows.


compact disc

Known by its abbreviation, CD, a compact disk is a polished metal platter capable of storing digital information. The most prevalent types of compact disks or those used by the music industry to store digital recordings and CD-ROMs used to store computer data. Both of these types of compact disk are read-only, which means that once the data has been recorded onto them, they can only be read, or played.

Another type of compact disk, generally called an erasable optical disk, can have its data erased and overwritten by new data. Currently, erasable optical storage is too slow to be used as a computer’s main storage facility, but as the speed improves and the cost comes down, optical storage devices are becoming a popular alternative to tape systems as a backup method.


comparison operator

Same as relational operator.


compatible

(n) Indicates that a product can work with or is equivalent to another, better-known product. The term is often used as a shorthand for IBM-compatible PC, a computer that is compatible with an IBM PC. Another term for a compatible is clone.

(adj) The ability of one device or program to work with another device or program. The term compatible implies different degrees of partnership. For example, a printer and a computer are said to be compatible if they can be connected to each other. An IBM compatible PC, on the other hand, is a computer that can run the same software as an IBM PC. (Note, however, that many manufacturers claim IBM compatibility even though their computers cannot run 100 percent of the software made for IBM PCs.)

Compatibility of two devices, such as printers, usually means that they react to software commands in the same way. Some printers achieve compatibility by tricking the software into believing that the printer is a different machine. This is called emulation.

Be aware, however, that hardware compatibility does not always extend to expansion slots. For example, two compatible printers may not accept the same font cartridges. Complete hardware compatibility is denoted by the term plug compatible.

Software products are compatible if they use the same data formats. For example, many programs are compatible with dBASE. This means that the files they produce can easily be transformed into a dBASE database or that they can import dBASE files.


compile

To transform a program written in a high-level programming language from source code into object code. Programmers write programs in a form called source code. Source code must go through several steps before it becomes an executable program. The first step is to pass the source code through a compiler, which translates the high-level language instructions into object code.

The final step in producing an executable program—after the compiler has produced object code—is to pass the object code through a linker. The linker combines modules and gives real values to all symbolic addresses.


compiler

A program that translates source code into object code. The compiler derives its name from the way it works, looking at the entire piece of source code and collecting and reorganizing the instructions. Thus, a compiler differs from an interpreter, which analyzes and executes each line of source code in succession, without looking at the entire program. The advantage of interpreters is that they can execute a program immediately. Compilers require some time before an executable program emerges. However, programs produced by compilers run much faster than the same programs executed by an interpreter.

Every high-level programming language (except strictly interpretive languages) comes with a compiler. In effect, the compiler is the language, because it defines which instructions are acceptable.

Because compilers translate source code into object code, which is unique for each type of computer, many compilers are available for the same language. For example, there is a FORTRAN compiler for PCs and another for Apple Macintosh computers. In addition, the compiler industry is quite competitive, so there are actually many compilers for each language on each type of computer. More than a dozen companies develop and sell C compilers for the PC.


complementary metal oxide semiconductor

See CMOS.


complex instruction set computer

See CISC.


Component Object Model

A model for binary code developed by Microsoft. The Component Object Model (COM) enables programmers to develop objects that can be accessed by any COM-compliant application. Both OLE and ActiveX are based on COM.


component software

Sometimes called componentware, software designed to work as a component of a larger application. A good analogy is the way personal computers are built up from a collection of standard components: memory chips, CPUs, buses, keyboards, mice, disk drives, monitors, etc. Because all of the interfaces between components are standardized, it is possible to mix components from different manufacturers in a single system.

Similarly, the goal of component software is to standardize the interfaces between software components so that they too can work together seamlessly. Two new standards—OLE and OpenDoc—are designed to help programmers develop components that can work together. Many analysts believe that component software is the natural extension of object-oriented programming and that it will become the standard programming paradigm for years to come.


componentware

See under component software.


composite video

A type of video signal in which all information—the red, blue, and green signals (and sometimes audio signals as well)— are mixed together. This is the type of signal used by televisions in the United States (see NTSC).

In contrast, most computers use RGB video, which consists of three separate signals for red, green, and blue. In general, RGB video produces sharper images than composite video does.


compound document

A document that contains elements from a variety of computer applications. For example, a single compound document might include text from a word processor, graphics from a draw program, and a chart from a spreadsheet application. Most importantly, each element in the compound document is stored in such a way that it can be manipulated by the application that created it.

Many computer experts believe that compound documents represent the most useful metaphor for utilizing computers because they allow people to mix different forms of expression rather than artificially separating them. With the emergence of OLE as an important standard, compound documents are likely to become more and more a part of everyday computing.


compression

See data compression.


CompuServe Information Service

Short for CompuServe Information Service, one of the first and largest online services. CompuServe supports a wide array of forums and provides many types of electronic-mail services. In addition, it is connected to hundreds of different database systems.


computer

A programmable machine. The two principal characteristics of a computer are:

•	It responds to a specific set of instructions in a well-defined manner.

•	It can execute a prerecorded list of instructions (a program).

Modern computers are electronic and digital. The actual machinery—wires, transistors, and circuits—is called hardware; the instructions and data are called software.

All general-purpose computers require the following hardware components:

memory: Enables a computer to store, at least temporarily, data and programs.

mass storage device: Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.

input device: Usually a keyboard or mouse, the input device is the conduit through which data and instructions enter a computer.

output device: A display screen, printer, or other device that lets you see what the computer has accomplished.

central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions.

In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.

Computers can be classified by size and power as follows:

personal computer: A small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.

workstation: A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.

minicomputer: A multi-user computer capable of supporting from 10 to hundreds of users simultaneously.

mainframe: A powerful multi-user computer capable of supporting many hundreds of users simultaneously.

supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second.


Computer Graphics Metafile

See CGM.


computer literacy

The level of expertise and familiarity someone has with computers. Computer literacy generally refers to the ability to use applications rather than to program. Individuals who are very computer literate are sometimes called power users.


computer science

The study of computers, including both hardware and software design. Computer science is composed of many broad disciplines, including artificial intelligence and software engineering. Most universities now offer bachelor, master, and doctorate degrees in computer science.


computer system

A complete, working computer. The computer system includes not only the computer, but also any software and peripheral devices that are necessary to make the computer function. Every computer system, for example, requires an operating system.


computer-aided design

See CAD.


computer-aided engineering

See CAE.


computer-aided instruction

Same as computer-based training. See under CBT.


computer-aided manufacturing

See CAM.


computer-based training

See CBT.


concatenate

To link together or join. For example, concatenating the three words in, as, and much yields the single word inasmuch. Computer manuals often refer to the process of concatenating strings, a string being any series of characters. You can also concatenate files by appending one to another.


concatenation

The act of linking together two or more objects.


conditional

Referring to an action that takes place only if a specific condition is met. Conditional expressions are one of the most important components of programming languages because they enable a program to act differently each time it is executed, depending on the input. Most programming languages use the word if for conditional expressions. For example, the conditional statement:

if x equals 1 exit

directs the program to exit if the variable x is equal to 1.


conference

Same as forum, an area in a bulletin board or online service in which participants can meet discuss a topic of common interest.


CONFIG.SYS

The configuration file for DOS systems. Whenever a DOS computer boots up, it reads the CONFIG.SYS file (if it exists) and executes any commands in it. The most common commands are BUFFERS= and FILES=, which enable you to specify the buffer size and the number of files that can be open simultaneously. In addition, you can enter commands that install drivers for devices.


configuration

The way a system is set up, or the assortment of components that make up the system. Configuration can refer to either hardware or software, or the combination of both. For instance, a typical configuration for a PC consists of 4MB (megabytes) main memory, a floppy drive, a hard disk, a VGA monitor, and the DOS and/or Windows operating system.

Many software products require that the computer have a certain minimum configuration. For example, the software might require a graphics display monitor and a video adapter, a particular microprocessor, and a minimum amount of main memory.

When you install a new device or program, you often need to configure it, which means to set various switches and jumpers (for hardware) and to define values of parameters (for software). For example, the device or program may need to know what type of video adapter you have and what type of printer is connected to the computer.

In DOS systems, you can configure the operating environment by placing commands in a file called CONFIG.SYS. These commands can install drivers for various devices. In the Macintosh operating systems, you configure the system through control panels. In the Windows operating system, you configure the system through the Control Panel.


configuration file

A file that contains configuration information for a particular program. When the program is executed, it consults the configuration file to see what parameters are in effect. The configuration file for DOS is called CONFIG.SYS. The Windows operating system stores configuration information in files with a .INI extension. The two most important configuration files are WIN.INI and SYS.INI.


configure

To set up a program or computer system for a particular application.


connect time

The amount of time a computer is logged in to a remote computer. Many online services charge users per connect time. Other services offer unlimited connect time for a flat monthly fee.


connectivity

A computer buzzword that refers to a program or device's ability to link with other programs and devices. For example, a program that can import data from a wide variety of other programs and can export data in many different formats is said to have good connectivity. On the other hand, computers that have difficulty linking into a network (many laptop computers, for example) have poor connectivity.


connector

The part of a cable that plugs into a port or interface to connect one device to another. Most connectors are either male (containing one or more exposed pins) or female (containing holes in which the male connector can be inserted).


connector

The part of a cable that plugs into a port or interface to connect one device to another. Most connectors are either male (containing one or more exposed pins) or female (containing holes in which the male connector can be inserted).


console

(1) The combination of display monitor and keyboard (or other device that allows input). Another term for console is terminal.

(2) Another term for monitor or display screen.

(3) A bank of meters and lights indicating a computer's status, and switches that allow an operator to control the computer in some way.


constant

In programming, a constant is a value that never changes. The other type of values that programs use is variables, symbols that can represent different values throughout the course of a program.

A constant can be

•	a number, like 25 or 3.6

•	a character, like a or $

•	a character string, like “this is a string”

Constants are also used in spreadsheet applications to place non-changing values in cells. In contrast, a spreadsheet formula can produce a different value each time the spreadsheet is opened or changed.


context sensitive

Refers to a program feature that changes depending on what you are doing in the program. For example, context-sensitive help provides documentation for the particular feature that you are in the process of using.


context switching

Same as task switching.


contiguous

Being immediately adjacent. For example, contiguous sectors on a disk are sectors that come one after the other. Frequently, a file stored on disk can become fragmented, which means that it is stored on non-contiguous sectors.


continuous tone

Refers to images that have a virtually unlimited range of color or shades of grays. Photographs and television images, for example, are continuous-tone images. In contrast, computer hardware and software is digital, which means that they can represent only a limited number of colors and gray levels. Converting a black-and-white continuous-tone image into a computer image is known as gray scaling.


continuous-form paper

A type of printing paper which consists of a single sheet or roll of paper, normally perforated at regular intervals so that sheets can be easily separated. Most continuous-form paper has holes punched along each side so that the paper can be pulled through the printer by a tractor-feed mechanism.


control character

A special, non-printing character. The ASCII character set defines 32 control characters, as shown in the table. Originally, these codes were designed to control teletype machines. Now, however, they are often used to control display monitors, printers, and other modern devices.


Control key

A key on PC keyboards labeled Ctrl. You use the Control key in the same way that you use the Shift key—keeping it pressed down while pressing another character. The result is a control key combination, which can have different meanings depending on which program is running. On Macintoshes, the Control key is called an Apple key or Command key.


Control key combination

A command issued by pressing a keyboard character in conjunction with the Control key. Manuals usually represent control key commands with the prefix CTRL- or CNTL-. For example, CTRL-N means the Control key and N pressed at the same time. Sometimes a control character is represented by a caret (for example, ^N is the same as CTRL-N).

What happens after you enter a Control key combination depends on what application is active. Certain Control key combinations are semi-standardized. For example, CTRL-C often has the same effect as the Break key—it interrupts a program. And Ctrl-X often exits the current  application.


control panel

A Macintosh utility that permits you to set many of the system parameters. For example, you can control the type of beeps the Mac makes and the sensitivity of the mouse. On older Macs (system 6 and earlier), control panels are called cdevs.

The Windows operating system has a Control Panel program that offers many of the same features as the Macintosh control panels.


control panel device

See cdev.


control program

(1) A program that enhances an operating system by creating an environment in which you can run other programs. Control programs generally provide a graphical interface and enable you to run several programs at once in different windows.

Control programs are also called operating environments.

(2) Another term for operating system.


controller

A device that controls the transfer of data from a computer to a peripheral device and vice versa. For example, disk drives, display screens, keyboards, and printers all require controllers.

In personal computers, the controllers are often single chips. When you purchase a computer, it comes with all the necessary controllers for standard components, such as the display screen, keyboard, and disk drives. If you attach additional devices, however, you may need to insert new controllers that come on expansion boards.

Controllers must be designed to communicate with the computer's expansion bus. There are three standard bus architectures for PCs—the AT bus, the Extended Industry Standard Architecture (EISA), and the SCSI bus. When you purchase a controller, therefore, you must ensure that it conforms to the bus architecture that your computer uses.


conventional memory

On DOS systems, conventional memory refers to the portion of memory that is available to normal programs. DOS systems have an address space of 1MB (megabyte), but the top 384K (called high memory) is reserved for system use. This leaves 640K of conventional memory. Everything above 1MB is either extended or expanded memory.


convergence

(1) The coming together of two or more disparate disciplines or technologies. For example, the so-called fax revolution was produced by a convergence of telecommunications technology, optical scanning technology, and printing technology.

(2) In graphics, convergence refers to how sharply an individual color pixel on a monitor appears. Each pixel is composed of three dots—a red, blue, and green one. If the dots are badly misconverged, the pixel will appear blurry. All monitors have some convergence errors, but they differ in degree.


convert

To change data from one format to another.


cooperative multitasking

A type of multitasking in which the process currently controlling the CPU must offer control to other processes. It is called cooperative because all programs must cooperate for it to work. If one program does not cooperate, it can hog the CPU. In contrast, preemptive multitasking forces applications to share the CPU whether they want to or not. Both the Macintosh and Windows operating systems are based on cooperative multitasking, whereas UNIX is based on preemptive multitasking.


coprocessor

A special-purpose processing unit that assists the CPU in performing certain types of operations. For example, a math coprocessor performs mathematical computations, particularly floating-point operations. Math coprocessors are also called numeric and floating-point coprocessors.

Some computers come with coprocessors built in. For others, you can add a coprocessor. A math coprocessor can increase a computer's speed and power dramatically, particularly if you are running programs that perform a lot of floating-point arithmetic (engineering and scientific applications, statistical analysis, and graphics). Note, however, that the program itself must be written to take advantage of the coprocessor. If the program contains no coprocessor instructions, the coprocessor will never be utilized.

In addition to math coprocessors, there are also graphics coprocessors for manipulating graphic images. These are often called accelerator boards.


copy

(v) (1) To copy a piece of data to a temporary location. In word processing, for example, copying refers to duplicating a section of a document and placing it in a buffer (sometimes called a clipboard). The term copy differs from cut, which refers to actually removing a section of a document and placing it in a buffer. After cutting or copying, you can move the contents of the buffer by pasting it somewhere else.

(2) In file management, the term copy refers to making a duplicate of a file.

(n) A duplicate of a piece of data, such as a file or a directory.


copy protection

Refers to techniques used to prevent the unauthorized copying of software. The idea of copy-protected software was created by software manufacturers who wanted to prevent software piracy—users copying programs and giving them to friends and colleagues free of charge.

As enticing an idea as it may be, copy protection has not proved to be a viable strategy. For one, it is practically impossible to create software that cannot be copied by a knowledgeable programmer. Second, many consumers shy away from copy-protected software because backup copies are difficult to make. Thus, if their original copy of the software is damaged, the user must contact the manufacturer for a new copy. Finally, some copy-protection techniques can actually damage other software on the system. For these reasons, copy-protected software is becoming less common.

Most software producers now protect their programs by issuing registration numbers with each package. When you install the software, you must enter the registration number. This does not prevent all piracy, but it limits it. In addition, users cannot get updates to a product unless they own the original diskettes and documentation.

An alternative strategy for dealing with the problem of software piracy is shareware, where users are actually encouraged to copy and disseminate programs. Shareware publishers rely on people's honesty to pay for the products used.


corrupted

Refers to data that has been damaged in some way.


Courier font

A common monospaced (fixed-pitch) font. This sentence is in Courier font. Most printers support the Courier font.


courseware

Software designed to be used in an educational program.


CP/M

Abbreviation of Control Program for Microprocessors. Created by Digital Research Corporation, CP/M was one of the first operating systems for personal computers. However, Digital Research Corporation made a critical strategic error by not agreeing to produce an operating system for the first IBM PC. According to the folklore, the president of Digital Research was flying his airplane when IBM came to call. IBM marched out and never looked back.

Instead, IBM turned to Microsoft Corporation, which developed MS-DOS. By the mid 1980s, MS-DOS had become the standard operating system for IBM-compatible personal computers. Although still used on some old models, CP/M is practically obsolete.


cps

Abbreviation of characters per second, a unit of measure used to describe the speed of dot-matrix and daisy-wheel printers. The speed of laser and ink-jet printers is described in terms of pages per minute (ppm).


CPU

Abbreviation of central processing unit, and pronounced as separate letters. The CPU is the brains of the computer. Sometimes referred to simply as the processor or central processor, the CPU is where most calculations take place. In terms of computing power, the CPU is the most important element of a computer system.

On large machines, CPUs require one or more printed circuit boards. On personal computers and small workstations, the CPU is housed in a single chip called a microprocessor.

Two typical components of a CPU are:

•	The arithmetic logic unit (ALU), which performs arithmetic and logical operations.

•	The control unit, which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.


CPU time

The amount of time the CPU is actually executing instructions. During the execution of most programs, the CPU sits idle much of the time while the computer fetches data from the keyboard or disk, or sends data to an output device. The CPU time of an executing program, therefore, is generally much less than the total execution time of the program. Multitasking operating systems take advantage of this by sharing the CPU among several programs.

CPU times are used for a variety of purposes: to compare the speed of two different processors, to gauge how CPU-intensive a program is, and to measure the amount of processing time being allocated to different programs in a multitasking environment.


crash

(n) A serious computer failure. A computer crash means that the computer itself stops working or that a program aborts unexpectedly. A crash signifies either a hardware malfunction or a very serious software bug.

If your computer crashes, it is not your fault. If the program is good and your hardware is functioning properly, there is nothing you can do to make your system crash.

(v) To fail or break. Other terms for crash include hang and bomb.


CRC

Abbreviation of cyclic redundancy check, a common technique for detecting data transmission errors. A number of file transfer protocols, including Zmodem, use CRC in addition to checksum.


crippled version

A demonstration version of a piece of software that has one or more critical features disabled. Many software companies distribute crippled versions of their applications free with the hope that users will get hooked and buy the full version.


crop

In computer graphics, to cut off the sides of an image to make it the proper size or to remove unwanted parts. Most graphics applications allow you to crop images with a clip feature.


crop marks

Printed or drawn lines indicating where the paper should be cut to produce the correct page size. Crop marks are necessary for offset printing because the original paper that goes through the printing press is usually larger than the final page size. Many desktop publishing systems are capable of automatically printing crop marks for camera-ready copy.


cross-platform

Refers to the capability of software or hardware to run identically on different platforms. Many applications for Windows and the Macintosh, for example, now produce binary-compatible files, which means that users can switch from one platform to the other without converting their data to a new format.

Cross-platform computing is becoming increasingly important as local-area networks become better at linking machines of different types.


CRT

Abbreviation of cathode-ray tube, the technology used in most televisions and computer display screens. A CRT works by moving an electron beam back and forth across the back of the screen. Each time the beam makes a pass across the screen, it lights up phosphor dots on the inside of the glass tube, thereby illuminating the active portions of the screen. By drawing many such lines from the top to the bottom of the screen, it creates an entire screenful of images.


Ctrl

See under Control key combination.


current

Refers to an object that is acting as a reference point. For example, the current directory is the same as the working directory or default directory. The current drive is the default mass storage device. In a spreadsheet application, the current cell is the active cell, the cell that you are manipulating at the moment.


cursor

(1) A special symbol, usually a solid rectangle or a blinking underline character, that signifies where the next character will be displayed on the screen. To type in different areas of the screen, you need to move the cursor. You can do this with the arrow keys, or with a mouse if your program supports it.

If you are running a graphics-based program, the cursor may appear as a small arrow, called a pointer. (The terms cursor and pointer are often used interchangeably.) In text processing, a cursor sometimes appears as an I-beam pointer, a special type of pointer that always appears between two characters. Note also that programs that support a mouse may use two cursors: a text cursor, which indicates where characters from the keyboard will be entered, and a mouse cursor for selecting items with the mouse.

(2) A device, similar in appearance to a mouse, that is used to sketch lines on a digitizing tablet. Cursors for digitizing tablets are sometimes called pucks.


cursor control keys

Special keys on computer keyboards that move the cursor. The arrow keys, for example, move the cursor up, down, right, and left. In addition, most keyboards have End, Home, Page Up, Page Down, and Backspace keys.


cursor position

The position of the cursor on the display screen. While in text mode, a display screen is capable of displaying a certain number of lines and a certain number of characters on each line. The cursor position is represented by the line number and the character number and signifies where the next character will be displayed. For example, cursor position 1,1 always indicates the upper-leftmost corner position on the terminal. Cursor position 10,30 indicates the 30th character position on the 10th line.


customer support

Service that computer and software manufacturers, and third-party service companies, offer to customers. For personal computer products, the following are common customer-support options:

mail-in service: The manufacturer will repair your equipment if you mail it in. Typical turnaround time is about four days. In some service plans, the manufacturer charges you for shipping expenses.

carry-in service: The manufacturer will repair your equipment, but you must deliver it to a local service site. This is sometimes called depot service.

on-site contract: For a monthly or annual fee, a repair person will come to your site to fix problems. (The fee is included in the purchase price of some machines.) Most on-site contracts guarantee that the service will be rendered within a fixed number of hours from when you report a problem.

hot lines: Many software manufacturers provide a phone number that you can call for advice and trouble-shooting. Often the number is toll-free. The quality of this type of support varies considerably from one company to another. Some hot lines are so good that they enable you to solve most problems yourself. Others are so bad that you are unable even to get through.

bulletin board system: Some companies maintain electronic bulletin boards (or forums within online services) staffed by service engineers. If you have a modem, you can report a problem to the bulletin board and a technician will respond. This can be convenient because bulletin boards are usually open 24 hours a day. Also, bulletin boards enable you to download software updates that correct known bugs.


cut

To remove an object from a document and place it in a buffer. In word processing, for example, cut means to move a section of text from a document to a temporary buffer. This is one way to delete text. However, because the text is transferred to a buffer, it is not lost forever. You can copy the buffer somewhere else in the document or in another document, which is called pasting. To move a section of text from one place to another, therefore, you need to first cut it and then paste it. This is often called cut-and-paste.

Most applications have only one buffer, sometimes called a clipboard. If you make two cuts in succession, the text from the original cut will be replaced by the text from the second cut.

Graphical user interfaces, such as MS-Windows and the Macintosh interface, allow you to cut and paste graphics as well as text.


cut-sheet feeder

See under sheet feeder.


cyber

A prefix used in a growing number of terms to describe new things that are being made possible by the spread of computers. Cyberphobia, for example, is an irrational fear of computers. Cyberpunk is a genre of science fiction that draws heavily on computer science ideas. Cyberspace is the non-physical terrain created by computer systems.


cyberspace

A metaphor for describing the non-physical terrain created by computer systems. Online systems, for example, create a cyberspace within which people can communicate with one another (via e-mail), do research, or simply window shop. Like physical space, cyberspace contains objects (files, mail messages, graphics, etc.) and different modes of transportation and delivery. Unlike real space, though, exploring cyberspace does not require any physical movement other than pressing keys on a keyboard or moving a mouse.

Some programs, particularly computer games, are designed to create a special cyberspace, one that resembles physical reality in some ways but defies it in others. In its extreme form, called virtual reality, users are presented with visual, auditory, and even tactile feedback that makes cyberspace feel real.


cycle time

A measurement of how quickly two back-to-back accesses of a memory chip can be made. Note that a DRAM chip’s cycle time is usually much longer than its access time, which measures only a single access. This is because DRAM chips require a pause between accesses.


cyclic redundancy check

See under CRC.


cylinder

A single track location on all the platters making up a hard disk. For example, if a hard disk has four platters, each with 600 tracks, then there will be 600 cylinders, and each cylinder will consist of 8 tracks (2 for each platter).


DA

Pronounced as separate letters, DA stands for desk accessory. See under desk accessory.


daisy chain

(n) A hardware configuration in which devices are connected one to another in a series. The SCSI interface, for example, supports a daisy chain of up to 7 devices.

(v) To connect devices in a daisy chain pattern.


daisy-wheel printer

A type of printer that produces letter-quality type. A daisy-wheel printer works on the same principle as a ball-head typewriter. The daisy wheel is a disk made of plastic or metal on which characters stand out in relief along the outer edge. To print a character, the printer rotates the disk until the desired letter is facing the paper. Then a hammer strikes the disk, forcing the character to hit an ink ribbon, leaving an impression of the character on the paper. You can change the daisy wheel to print different fonts.

Daisy-wheel printers cannot print graphics, and in general they are noisy and slow, printing from 10 to about 75 characters per second. As the price of laser ink-jet printers has declined, and the quality of dot-matrix printers has improved, daisy-wheel printers have become almost obsolete.


DAT

Acronym for digital audio tape, a type of magnetic tape that uses an ingenious scheme called helical scan to record data. A DAT cartridge is slightly larger than a credit card and contains a magnetic tape that can hold from 2 to 5 gigabytes of data. It can support data transfer rates of about 10 megabytes per minute. Like other types of tapes, DATs are sequential-access media.

The most common format for DAT cartridges is DDS (digital data storage).


data

(1) Information, usually formatted in a special way. All software is divided into two general categories: data and programs. Programs are collections of instructions for manipulating data.

Data can exist in a variety of forms—as numbers or text on pieces of paper, as bits and bytes stored in electronic memory, or as facts stored in a person's mind.

Strictly speaking, data is the plural of datum, a single piece of information. In practice, however, people use data as both the singular and plural form of the word.

(2) The term data is often used to distinguish binary  machine-readable information from textual human-readable information. For example, some applications make a distinction between data files (files that contain binary  data) and text files (files that contain ASCII data).

(3) In database management systems, data files are the files that store the database information, whereas other files, such as index files and data dictionaries, store administrative information.


data bus

See under bus.


data communications

See communications.


data compression

Storing data in a format that requires less space than usual. Compressing data is the same as packing data.

Data compression is particularly useful in communications because it enables devices to transmit the same amount of data in fewer bits. There are a variety of data compression techniques, but only a few have been standardized. The CCITT has defined a standard data compression technique for transmitting faxes (Group 3 standard) and a compression standard for data communications through modems (CCITT V.42bis). In addition, there are file compression formats, such as ARC and ZIP.

Data compression is also widely used in backup utilities, spreadsheet applications, and database management systems. Certain types of data, such as bit-mapped graphics, can be compressed to a small fraction of their normal size.

In recent years, compression boards have appeared in the marketplace. These are expansion boards that automatically compress data as it is written to a disk and then decompress the data when it is fetched. The data compression is invisible to the user but can effectively double or triple the capacity of a disk drive.


data dictionary

In database management systems, a file that defines the basic organization of a database. A data dictionary contains a list of all files in the database, the number of records in each file, and the names and types of each field. Most database management systems keep the data dictionary hidden from users to prevent them from accidentally destroying its contents.

Data dictionaries do not contain any actual data from the database, only bookkeeping information for managing it. Without a data dictionary, however, a database management system cannot access data from the database.


data encryption

See under encryption.


data entry

The process of entering data into a computerized database or spreadsheet. Data entry can be performed by an individual typing at a keyboard or by a machine entering data electronically.


data processing

Refers to a class of programs that organize and manipulate data, usually large amounts of numeric data. Accounting programs are the prototypical examples of data processing applications. In contrast, word processors, which manipulate text rather than numbers, are not usually referred to as data processing applications.


data rate

Short for data transfer rate.


data structure

In programming, the term data structure refers to a scheme for organizing related pieces of information. The basic types of data structures include:

•	files

•	lists

•	arrays

•	records

•	trees

•	tables

Each of these basic structures has many variations and allows different operations to be performed on the data.


data transfer rate

The speed with which data can be transmitted from one device to another. Data rates are often measured in megabits (million bits) or megabytes (million bytes) per second.

Another term for data transfer rate is throughput.


data type

In programming, classification of a particular type of information. It is easy for humans to distinguish between different types of data. We can usually tell at a glance whether a number is a percentage, a time, or an amount of money. We do this through special symbols—%, :, and $—that indicate the data's type. Similarly, a computer uses special symbols to keep track of the different types of data it processes.

Most programming languages require the programmer to declare the data type of every data object, and most database systems require the user to specify the type of each data field. The available data types vary from one programming language to another, and from one database application to another, but the following usually exist in one form or another:

integer: In more common parlance, whole number; a number that has no fractional part.

floating-point: A number with a decimal point. For example, 3 is an integer, but 3.5 is a floating-point number.

character (text): Readable text


database

(1) A collection of information organized in such a way that a computer program can quickly select desired pieces of data. You can think of a database as an electronic filing system.

Traditional databases are organized by fields, records, and files. A field is a single piece of information; a record is one complete set of fields; and a file is a collection of records. For example, a telephone book is analogous to a file. It contains a list of records, each of which consists of three fields: name, address, and telephone number.

An alternative concept in database design is known as Hypertext. In a Hypertext database, any object, whether it be a piece of text, a picture, or a film, can be linked to any other object. Hypertext databases are particularly useful for organizing large amounts of disparate information, but they are not designed for numerical analysis.

To access information from a database, you need a database management system (DBMS) . This is a collection of programs that enables you to enter, organize, and select data in a database.

(2) Increasingly, the term database is used as shorthand for database management system.


database management system (DBMS)

A collection of programs that enables you to store, modify, and extract information from a database. There are many different types of DBMSs, ranging from small systems that run on personal computers to huge systems that run on mainframes. The following are examples of database applications:

•	computerized library systems

•	automated teller machines

•	flight reservation systems

•	computerized parts inventory systems

From a technical standpoint, DBMSs can differ widely. The terms relational, network, flat, and hierarchical all refer to the way a DBMS organizes information internally. The internal organization can affect how quickly and flexibly you can extract information.

Requests for information from a database are made in the form of a query, which is a stylized question. For example, the query

SELECT ALL WHERE NAME = “SMITH” AND AGE > 35

requests all records in which the NAME field is SMITH and the AGE field is greater than 35. The set of rules for constructing queries is known as a query language. Different DBMSs support different query languages, although there is a semi-standardized query language called SQL (structured query language). Sophisticated languages for managing database systems are called fourth-generation languages, or 4GLs for short.

The information from a database can be presented in a variety of formats. Most DBMSs include a report writer program that enables you to output data in the form of a report. Many DBMSs also include a graphics component that enables you to output information in the form of graphs and charts.


dBASE

A popular database management system produced by Ashton Tate Corporation. The original version, called Vulcan, was created by Wayne Ratliff. In 1981, Ashton-Tate bought Vulcan and marketed it as dBASE II. Subsequent versions with additional features are known as dBASE III, dBASE III+, and dBASE IV, all of which are currently owned and developed by Borland Corporation.

The dBASE format for storing data has become a de facto standard, and is supported by nearly all database management and spreadsheet systems. Even systems that do not use the dBASE format internally are able to import and export data in dBASE format.


DBMS

See database management system.


DDE

Acronym for Dynamic Data Exchange, an interprocess communication (IPC)  system built into the Macintosh, Windows, and OS/2 operating systems. DDE enables two running applications to share the same data. For example, DDE makes it possible to insert a spreadsheet chart into a document created with a word processor. Whenever the spreadsheet data changes, the chart in the document changes accordingly.

Although the DDE mechanism is still used by many applications, it is being supplanted by OLE, which provides greater control over shared data.


de facto standard

A format, language, or protocol that has become a standard not because it has been approved by a standards organization but because it is widely used and recognized by the industry as being standard. Some examples of de facto standards include:

•	Hayes command set for controlling modems

•	Kermit Communications Protocol

•	Xmodem Communications Protocol

•	Hewlett-Packard Printer Control Language (PCL) for laser printers.

•	PostScript page description language for laser printers


debug

To find and remove errors (bugs) from a program or design.


debugger

A special program used to find errors (bugs) in other programs. A debugger allows a programmer to stop a program at any point and examine and change the values of variables.


decimal

Refers to numbers in base 10 (the numbers we use in everyday life). For example, the following are decimal numbers:

9

100345000

-256

Note that a decimal number is not necessarily a number with a decimal point in it. Numbers with decimal points (that is, numbers with a fractional part) are called fixed-point or floating-point numbers.

In addition to the decimal format, computer data is often represented in binary , octal, and hexadecimal formats.


declare

In programming, to declare is to define the name and data type of a variable or other programming construct. Many programming languages, including C and Pascal, require you to declare variables before using them.


decrement

To subtract. For example, if you count down consecutively from 10 to 0, you decrement by 1. If you count down by twos, you decrement by 2. The opposite of decrementing is incrementing.


decryption

The process of decoding data that has been encrypted into a secret format. Decryption requires a secret key or password.


dedicated

Reserved for just one use. In communications, a dedicated channel is a line reserved exclusively for one type of communication. This is the same as a leased line or private line.

A dedicated server is a single computer in a network reserved for serving the needs of the network. For example, some networks require that one computer be set aside to manage communications between all the other computers. A dedicated server could also be a computer that manages printer resources. Note, however, that not all servers are dedicated. In some networks, it is possible for a computer to act as a server and perform other functions as well.

The opposite of dedicated is general purpose.


default

A value or setting that a device or program automatically selects if you do not specify a substitute. For example, word processors have default margins and default page lengths that you can override or reset.

The default drive is the disk drive the computer accesses unless you specify a different disk drive. Likewise, the default directory is the directory the operating system searches unless you specify a different directory.

The default can also be an action that a device or program will take. For example, some word processors generate backup files by default.


defragment

To optimize a disk by unfragmenting files. See under fragmentation.


delete

To remove or erase. For example, deleting a character means removing it from a file or erasing it from the display screen. Deleting a file means erasing it from a disk. Note that, unlike cutting, deleting does not necessarily place the removed object in a buffer from where it can be recovered.


Delete key

Often abbreviated as Del, the Delete key is used to remove characters and other objects. On PCs, the Delete key generally removes the character immediately under the cursor (or to the right of the insertion point), or the highlighted text or object. Note the difference between the Delete key, which deletes the character under the cursor, and the Backspace key, which deletes the character to the left of the cursor or insertion point. On Macintoshes, the Delete key generally acts like a PC’s Backspace key, deleting the character immediately in front of the insertion point.


delimiter

A punctuation character or group of characters that separates two names or two pieces of data, or marks the beginning or end of a programming construct. Delimiters are used in almost every computer application. For example, in specifying DOS pathnames, the backslash (\) is the delimiter that separates directories and filenames. Other common delimiters include the comma (,), semicolon (;), quotes (“), and braces ({}).


demand paging

In virtual memory systems, demand paging is a type of swapping in which pages of data are not copied from disk to RAM until they are needed. In contrast, some virtual memory systems use anticipatory paging, in which the operating system attempts to anticipate which data will be needed next and copies it to RAM before it is actually required.


density

How tightly information is packed together on a storage medium (tape or disk). A higher density means that data are closer together, so the medium can hold more information. Floppy disks can be single-density, double-density, high-density, or extra-high-density. To use a double-density, high-density, or extra-high-density disk, you must have a disk drive that supports the density level. Density, therefore, can refer both to the media and the device.

The table shows the storage capacities of double- and high-density floppies on the PC and the Apple Macintosh. Note that the only difference between double-density and high-density disks is that the high-density disks were found to be higher quality during the testing process. High-quality disks are sold as high-density, and lower-quality disks are sold as double-density. It is often possible, therefore, to format a double-density disk as a high-density disk, but this practice is not encouraged.


descender

In typography, the portion of a lowercase letter that falls below the baseline. In the English alphabet, 5 letters have descenders: g, j, p, q, and y.


desk accessory (DA)

On Apple Macintoshes, a utility—that is, a small, stand-alone program designed to perform one small task. For example, Apple's Calculator is a desk accessory.


desktop

In graphical user interfaces, a desktop is the metaphor used to portray file systems. Such a desktop consists of pictures, called icons, that show cabinets, files, folders, and various types of documents (that is, letters, reports, pictures). You can arrange the icons on the electronic desktop just as you can arrange real objects on a real desktop—moving them around, putting one on top of another, reshuffling them, and throwing them away.


desktop model computer

A computer designed to fit comfortably on top of a desk, typically with the monitor sitting on top of the computer. Desktop model computers are broad and low, whereas tower model computers are narrow and tall. Because of their shape, desktop model computers are generally limited to three internal mass storage devices. Desktop models designed to be very small are sometimes referred to as slimline models.


desktop publishing

Using a personal computer or workstation to produce high-quality printed documents. A desktop publishing system allows you to use different typefaces, specify various margins and justifications, and embed illustrations and graphs directly into the text. The most powerful desktop publishing systems enable you to create illustrations, while less powerful systems let you insert illustrations created by other programs.

As word-processing programs become more and more powerful, the line separating such programs from desktop publishing systems is becoming blurred. In general, though, desktop publishing applications give you more control over typographical characteristics, such as kerning, and provide more support for full-color output.

A particularly important feature of desktop publishing systems is that they enable you to see on the display screen exactly how the document will appear when printed. Systems that support this feature are called WYSIWYGs (what you see is what you get).

Until recently, hardware costs made desktop publishing systems impractical for most uses. But as the prices of personal computers and printers have fallen, desktop publishing systems have become increasingly popular for producing newsletters, brochures, books, and other documents that formerly required a typesetter.

Once you have produced a document with a desktop publishing system, you can output it directly to a printer or you can produce a PostScript file which you can then take to a service bureau. The service bureau has special machines that convert the PostScript file to film, which can then be used to make plates for offset printing. Offset printing produces higher-quality documents, especially if color is used, but is generally more expensive than laser printing.


destination

Many computer commands move data from one file to another or from one storage device to another. This is referred to as moving the data from the source to the destination (or target). The term is also used as an adjective, as in destination file or destination device.


device

Any machine or component that attaches to a computer. Examples of devices include disk drives, printers, mice, and modems. These particular devices fall into the category of peripheral devices because they are separate from the main computer. Display monitors and keyboards are also devices, but because they are integral parts of the computer, they are not considered peripheral.

Every device, whether peripheral or not, requires a program called a device driver that acts as a translator, converting general commands from an application into specific commands that the device understands.


device dependent

Like machine-dependent, device-dependent refers to programs that can run only on a certain type of hardware.


device driver

See driver.


dial-up access

Refers to connecting a device to a network via a modem and a public telephone network. Dial-up access is really just like a phone connection, except that the parties at the two ends are computer devices rather than people. Because dial-up access uses normal telephone lines, the quality of the connection is not always good and data rates are limited. In the past, the maximum data rate with dial-up access was 28.8 Kbps (28,800 bits per second), but new technologies such as ISDN are providing faster rates.

An alternative way to connect two computers is through a leased line, which is a permanent connection between two devices. Leased lines provide faster throughput and better quality connections, but they are also more expensive.


dialog box

A box that appears on a display screen to present information or request input. Typically, dialog boxes are temporary—they disappear once you have entered the requested information.

In the Macintosh and Microsoft Windows interfaces, there is a convention that any menu option followed by ellipsis points ( . . . ) will, when selected, bring up a dialog box. Options without ellipsis points are executed directly.


digital

Describes any system based on discontinuous data or events. Computers are digital machines because at their most basic level they can distinguish between just two values, 0 and 1, or off and on. There is no simple way to represent all the values in between, such as 0.25. All data that a computer processes must be encoded digitally, as a series of zeroes and ones.

The opposite of digital is analog. A typical analog device is a clock in which the hands move continuously around the face. Such a clock is capable of indicating every possible time of day. In contrast, a digital clock is capable of representing only a finite number of times (every tenth of a second, for example).

In general, humans experience the world analogically. Vision, for example, is an analog experience because we perceive infinitely smooth gradations of shapes and colors. Most analog events, however, can be simulated digitally. Photographs in newspapers, for instance, consist of an array of dots that are either black or white. From afar, the viewer does not see the dots (the digital form), but only lines and shading, which appear to be continuous. Although digital representations are approximations of analog events, they are useful because they are relatively easy to store and manipulate electronically. The trick is in converting from analog to digital, and back again.

This is the principle behind compact discs (CDs). The music itself exists in an analog form, as waves in the air, but these sounds are then translated into a digital form that is encoded onto the disk. When you play a compact disc, the CD player reads the digital data, translates it back into its original analog form, and sends it to the amplifier and eventually the speakers.

Internally, computers are digital because they consist of discrete units called bits that are either on or off. But by combining many bits in complex ways, computers simulate analog events. In one sense, this is what computer science is all about.


digital audio tape

See DAT.


digital camera

A camera that stores images digitally rather than recording them on film. Once a picture has been taken, it can be downloaded to a computer system, and then manipulated with a graphics program and printed. Unlike film photographs, which have an almost infinite resolution, digital photos are limited by the amount of memory in the camera, the optical resolution of the digitizing mechanism, and, finally, by the resolution of the final output device. Even the best digital cameras connected to the best printers cannot produce film-quality photos. However, if the final output device is a laser printer, it doesn’t really matter whether you take a real photo and then scan it, or take a digital photo. In both cases, the image must eventually be reduced to the resolution of the printer.

The big advantage of digital cameras is that making photos is both inexpensive and fast because there is no film processing. Interestingly, one of the biggest boosters of digital photography is Kodak, the largest producer of film. Kodak developed the Kodak PhotoCD format, which has become the de facto standard for storing digital photographs.


digital cash

A system that allows a person to pay for goods or services by transmitting a number from one computer to another.  Like the serial numbers on real dollar bills, the digital cash numbers are  unique. Each one is issued by a bank and represents a specified sum of real money. One of the key features of digital cash is that, like real cash, it is anonymous and reusable. That is, when a digital cash amount is sent from a buyer to a vendor, there is no way to obtain information about the buyer. This is one of the key differences between digital cash and credit card systems. Another key difference is that a digital cash certificate can be reused.

Digital cash transactions are expected to become commonplace by the year 2000. However, there a number of competing protocols, and it is unclear which ones will become dominant. Most digital cash systems start with a participating bank that issues cash numbers or other unique identifiers that carry a given value, such as five dollars.  To obtain such a certificate, you must have an account at the bank; when you purchase digital cash certificates, the money is withdrawn from your account. You transfer the certificate to the vendor to pay for a product or service, and the vendor deposits the cash number in any participating bank or retransmits it to another vendor.  For large purchases, the vendor can check the validity of a cash number by contacting the issuing bank.


digital monitor

A monitor that accepts digital rather than analog signals. All monitors (except flat-panel displays) use CRT technology, which is essentially analog. The term digital, therefore, refers only to the type of input received from the video adapter. A digital monitor then translates the digital signals into analog signals that control the actual display.

Although digital monitors are fast and produce clear images, they cannot display continuously variable colors. Consequently, only low-quality video standards, such as MDA, CGA, and EGA, specify digital signals. VGA and SVGA, on the other hand, require an analog monitor. Some monitors are capable of accepting either analog or digital signals.


digital signal processing

See DSP.


Digital Video Interactive

See DVI.


digitize

To translate into a digital form. For example, optical scanners digitize images by translating them into bit maps. It is also possible to digitize sound, video, and any type of movement. In all these cases, digitization is performed by sampling at discrete intervals. To digitize sound, for example, a device measures pitch and volume many times per second. These numeric values can then be recorded digitally.


digitizing tablet

An input device that enables you to enter drawings and sketches into a computer. A digitizing tablet consists of an electronic tablet and a cursor or pen. A cursor (also called a puck) is similar to a mouse, except that it has a window with cross hairs for pinpoint placement, and it can have as many as 16 buttons. A pen (also called a stylus) looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronics that enable it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer.

For digitizing tablets, each point on the tablet represents a point on the display screen in a fixed manner. This differs from mice, in which all movement is relative to the current cursor position. The static nature of digitizing tablets makes them particularly effective for tracing drawings. Most modern digitizing tablets also support a mouse emulation mode, in which the pen or cursor acts like a mouse.

Digitizing tablets are also called digitizers, graphics tablets, touch tablets, or simply tablets.


DIN connector

DIN is an acronym for Deutsche Industrinorm, the standards-setting organization for Germany. A DIN connector is a connector that conforms to one of the many standards defined by DIN. DIN connectors are used widely in personal computers. For example, the keyboard connector for PCs is a DIN connector.


dingbat

A small picture, such as a star or a pointing finger, that can be inserted into a document. Many sets of dingbats are available as a special font. One of the most popular is Zapf dingbats, named after its creator, Hermann Zapf.


DIP

Acronym for dual in-line package, a type of chip housed in a rectangular casing with two rows of connecting pins on either side.


DIP switch

A DIP (dual in-line package) switch is a series of tiny switches built into circuit boards. The housing for the switches, which has the same shape as a chip, is the DIP.

DIP switches enable you to configure a circuit board for a particular type of computer or application. The installation instructions should tell you how to set the switches. DIP switches are always toggle switches, which means they have two possible positions—on or off. (Instead of on and off, you may see the numbers 1 and 0.)

One of the historic advantages of the Macintosh over the PC was that it allowed you to configure circuit boards by entering software commands instead of setting DIP switches. However, the new Plug & Play standard developed by Microsoft makes DIP switches obsolete for PC expansion cards too.


direct access

Same as random access.


direct memory access

See DMA.


direct-connect modem

A modem that connects directly to a telephone line via modular connectors rather than requiring an acoustic coupler. Almost all modern modems are direct-connect.


directive

Same as command.


directory

A special kind of file used to organize other files into a hierarchical structure. Directories contain bookkeeping information about files that are, figuratively speaking, beneath them. You can think of a directory as a folder or cabinet that contains files and perhaps other folders. In fact, many graphical user interfaces, such as the Macintosh interface, use the term folder instead of directory.

Computer manuals often describe directories and file structures in terms of an inverted tree. The files and directories at any level are contained in the directory above them. To access a file, you may need to specify the names of all the directories above it. You do this by specifying a path.

The topmost directory in any file is called the root directory. A directory that is below another directory is called a subdirectory. A directory above a subdirectory is called the parent directory.

To read information from, or write information into, a directory, you must use an operating system command. You cannot directly edit directory files. For example, the DIR command in DOS reads a directory file and displays its contents.


disc

Alternative spelling of disk. Disc is often used for optical discs, while disk generally refers to magnetic discs, but there is no real rule.


discretionary hyphen

See under hyphenation.


disk

A round plate on which data can be encoded. There are two basic types of disks: magnetic disks and optical disks.

A magnetic disk is like a phonograph record, except that the data is encoded as microscopic magnetized needles on the disk's surface rather than as grooves in the vinyl. Also, you can record and erase data on a magnetic disk any number of times, just as you can with a cassette tape. Magnetic disks come in a number of different forms:

floppy disk: A typical 5¼-inch floppy disk can hold 360K or 1.2MB (megabytes). Microfloppies (3½-inch floppies) normally store 720K, 1.2MB or 1.44MB of data.

hard disk: Hard disks can store anywhere from 20MB to more than 3GB. Hard disks are also from 2 to 20 times faster than floppy disks.

removable cartridge: Removable cartridges are hard disks encased in a metal or plastic cartridge, so you can remove them just like a floppy disk. Removable cartridges are very fast, often faster than fixed hard disks. A typical cartridge has a capacity of about 80MB.

Optical disks record data by burning microscopic holes in the surface of the disk with a laser. To read the disk, another laser beam shines on the disk and detects the holes by changes in the reflection pattern.

Optical disks have a much larger data capacity than magnetic disks, but they are slower.

Optical disks come in three forms:

CD-ROM: Most optical disks are read-only. When you purchase them, they are already filled with data. You can read the data from a CD-ROM, but you cannot modify, delete, or write new data.

WORM: Stands for write-once, read-many. WORM disks can be written on once and then read any number of times; however, you need a special WORM disk drive to write data onto a WORM disk.

erasable optical (EO): EO disks can be read to, written to, and erased just like magnetic disks.

The machine that spins a disk is called a disk drive. Within each disk drive is one or more heads (often called read/write heads) that actually read and write data.

Accessing data from a disk is not as fast as accessing data from main memory, but disks are cheaper and more stable. Unlike RAM, disks hold on to data even when the computer is turned off. Consequently, disks are the storage medium of choice for most types of data. Another storage medium is the magnetic tape. But tapes are used only for backup and archiving because they are sequential-access devices (to access data in the middle of a tape, the tape drive must pass through all the preceding data).

A new disk, called a blank disk, has no data on it. Before you can store data on a blank disk, however, you must format it. In DOS systems, disks are formatted with the FORMAT command. When you execute the FORMAT command, the operating system allocates space for directories and other bookkeeping information. Every operating system formats disks somewhat differently, so a disk formatted by one operating system usually cannot be read by another operating system.


disk cache

A portion of RAM used to speed up access to data on a disk. The RAM can be part of the disk drive itself (sometimes called a hard disk cache) or it can be general-purpose RAM in the computer that is reserved for use by the disk drive (sometimes called a soft disk cache). Hard disk caches are more effective, but they are also much more expensive.

In both cases, a disk cache works by storing the most recently accessed data in the RAM cache. When a program needs to access new data, the operating system first checks to see if the data is in the cache before reading it from the disk. Because computers can access data from RAM much faster than from a disk, disk caching can significantly increase performance. Many cache systems also attempt to predict what data will be requested next so they can place that data in the cache ahead of time.

Although caching improves performance, there is some risk involved. If the computer crashes (due to a power failure, for example), the system may not have time to copy the cache back to the disk. In this case, whatever changes you made to the data will be lost. Usually, however, the cache system updates the disk frequently so that even if you lose some data, it will not be much. A special type of disk cache, called a write-thru cache, removes the risk of losing data because it only caches data for read operations; write operations are always sent directly to the disk.


disk controller

A chip and associated circuitry that is responsible for controlling a disk drive. There are different controllers for different interfaces. For example, an IDE interface requires an IDE controller and a SCSI interface requires a SCSI controller. On Macintosh computer systems, the disk controller is built into the motherboard. On PCs, the disk controller is sometimes housed on a separate card.


disk crash

See under head crash.


disk drive

A machine that reads data from and writes data onto a disk. A disk drive resembles a stereo turntable in that it rotates the disk very fast. It has one or more heads that read and write data.

There are different types of disk drives for different types of disks. For example, a hard disk drive reads and writes hard disks, and a floppy drive accesses floppy disks. A magnetic disk drive reads magnetic disks, and an optical drive reads optical disks.

Disk drives can be either internal (housed within the computer) or external (housed in a separate box that connects to the computer).


disk operating system

See DOS.


disk optimizer

A program that makes a disk more efficient by defragmenting the disk. Fragmentation occurs naturally when a disk is used often.


disk pack

A stack of removable hard disks encased in a metal or plastic container.


diskette

Same as floppy disk.


diskless workstation

A workstation or PC on a local-area network (LAN)  that does not have its own disk. Instead, it stores files on a network file server. Diskless workstations can reduce the overall cost of a LAN because one large-capacity disk drive is usually less expensive than several low-capacity drives. In addition, diskless workstations can simplify backups and security because all files are in one place—on the file server. Also, accessing data from a large remote file server is often faster than accessing data from a small local storage device.

One disadvantage of diskless workstations, however, is that they are useless if the network fails.

When the workstation is a PC, it is often called a diskless PC.


display

(v) To make data or images appear on a monitor.

(n) Short for display screen.


display adapter

Same as video adapter.


display screen

The display part of a monitor. Most display screens work under the same principle as a television, using a cathode ray tube (CRT). Consequently, the term CRT is often used in place of display screen.


distributed database

A database that consists of two or more data files located at different sites on a computer network. Because the database is distributed, different users can access it without interfering with one another. However, the DBMS must periodically synchronize the scattered databases to make sure that they all have consistent data.


distributed processing

Refers to any of a variety of computer systems that use more than one computer, or processor, to run an application. This includes parallel processing, in which a single computer uses more than one CPU to execute programs. More often, however, distributed processing refers to local-area networks (LANs)  designed so that a single program can run simultaneously at various sites. Most distributed processing systems contain sophisticated software that detects idle CPUs on the network and parcels out programs to utilize them.

Another form of distributed processing involves distributed databases, databases in which the data is stored across two or more computer systems. The database system keeps track of where the data is so that the distributed nature of the database is not apparent to users.


dithering

Creating the illusion of new colors and shades by varying the pattern of dots. Newspaper photographs, for example, are dithered. If you look closely, you can see that different shades of gray are produced by varying the patterns of black and white dots. There are no gray dots at all. The more dither patterns that a device or program supports, the more shades of gray it can represent. In printing, dithering is usually called halftoning, and shades of gray are called halftones.

Note that dithering differs from gray scaling. In gray scaling, each individual dot can have a different shade of gray.


DMA

Abbreviation of direct memory access, a technique for transferring data from main memory to a device without passing it through the CPU. Computers that have DMA channels can transfer data to and from devices much more quickly than computers without a DMA channel can. This is useful for making quick backups and for real-time applications.

Some expansion boards, such as CD-ROM cards, are capable of accessing the computer’s DMA channel. When you install the board, you must specify which DMA channel is to be used, which sometimes involves setting a jumper or DIP switch.


DNS

Short for Domain Name System (or Service), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address.  For example, the domain name microsoft.com would be translated to 198.105.232.4. You can see that they're the same by substituting the number for the name in the URL http://www.microsoft.com and entering it in a Web browser.

The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.


docking station

A platform into which you can install a portable computer. The docking station typically contains slots for expansion cards, bays for storage devices, and connectors for peripheral devices, such as printers and monitors. Once inserted in a docking station, the portable computer essentially becomes a desktop model computer. When it is taken out, it becomes a portable computer again. Most importantly, the same data is accessible in both modes because it resides on the portable computer’s drives. The idea behind docking stations is to let you simultaneously enjoy the expansion possibilities of desktop model computers with the portability of notebook computers. In addition, the docking station enables you to use a full-size keyboard and monitor when you’re not traveling.

There is no standard for docking stations, so you must purchase one that is made specifically for your type of portable computer.


document

(1) In the PC world, a file created with a word processor. In addition to text, documents can contain graphics, charts, and other objects.

Increasingly, the line separating word processing files from files produced by other applications is becoming blurred. A word processing application can produce graphics and a graphics application can produce words. This trend is accelerating with new technologies such as OLE and OpenDoc that allow an application to combine many components. Consequently, the term document is used more and more to describe any file produced by an application. Interestingly, this is the way the term has always been used in Macintosh environments.

(2) To enter written explanations. For example, programmers are always exhorted to document their code by inserting comments.


documentation

Instructions for using a computer device or program. Documentation can appear in a variety of forms, the most common being manuals. When you buy a computer product (hardware or software), it almost always comes with one or more manuals that describe how to install and operate the product. In addition, many software products include an online version of the documentation that you can display on your screen or print out on a printer. A special type of online documentation is a help system, which has the documentation embedded into the program. Help systems are often called context-sensitive because they display different information depending on the user’s position (context) in the application.

Documentation is often divided into the following categories:

installation: Describes how to install a program or device but not how to use it.

reference: Detailed descriptions of particular items presented in alphabetical order. Reference documentation is designed for people who are already somewhat familiar with the product but need reminders or very specific information about a particular topic.

tutorial: Teaches a user how to use the product. Tutorials move at a slower pace than reference manuals and generally contain less detail.

A frequent lament from computer users is that their documentation is inscrutable. Fortunately, this situation is improving, thanks largely to advances in help systems and online tutorials. These forms of documentation make it much easier to deliver the specific information a user needs when he or she needs it.


domain

A group of computers and devices on a network that are administered as a unit with common rules and procedures.  Within the Internet, domains are defined by the IP address. All devices sharing a common part of the IP address are said to be in the same domain.


domain name

A name that identifies an IP address. For example, the domain name microsoft.com represents the IP address 198.105.232.4.  Domain names are used in URLs to identify particular Web pages. For example, in the URL http://www.sandybay.com/pc-web, the domain name is sandybay.com.

Every domain name has a suffix that indicates which top-level domain it belongs to. There are only a limited number of such domains. For example:

•	gov - Government agencies

•	edu - Educational institutions

•	org - Organizations (nonprofit)

•	mil - Military

•	com - commercial business

•	net - Network organizations

•	ca - Canada

•	th - Thailand

Because the Internet is based on IP addresses, not domain names, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses.


Domain Name Service (DNS)

See DNS.


DOS

Acronym for disk operating system. The term DOS can refer to any operating system, but it is most often used as a shorthand for MS-DOS (Microsoft disk operating system). Originally developed by Microsoft for IBM, MS-DOS is the standard operating system for IBM-compatible personal computers.

The initial versions of DOS were very simple and resembled another operating system called CP/M. Subsequent versions have become increasingly sophisticated as they have incorporated features of minicomputer operating systems. However, DOS is still a 16-bit operating system, does not support multiple users or multitasking, and has a built-in limitation of 1MB of memory. To exceed this limit, you need a special memory system called EMS (Expanded Memory Specification).

For some time, it has been widely acknowledged that DOS is insufficient for modern computer applications. Microsoft Windows helped alleviate some problems, but until Windows 95, it sat on top of DOS and relied on DOS for many services. New operating systems, including Windows 95 and OS/2 Warp, do not rely on DOS to the same extent, although they can execute DOS-based programs. It is expected that as these operating systems gain market share, DOS will eventually disappear. In the meantime, both IBM and Novell are competing with Microsoft with their own versions of DOS, called PC-DOS and Novell DOS, respectively.


dot

(1) Same as the period character (.). In DOS, Windows, and OS/2 systems, the dot is used to separate a filename from its extension. For example, the filename CONFIG.SYS is pronounced config-dot-sys.

(2) In bit-mapped representations, a dot is a single point, the smallest identifiable part of an image. Laser printers, for example, create characters and images by printing patterns of dots. Likewise, monitors display images as arrays of dots. The resolutions of devices are often measured in dots per inch (dpi).


dot pitch

A measurement that indicates the vertical distance between each pixel on a display screen. Measured in millimeters, the dot pitch is one of the principal characteristics that determines the quality of display monitors. The lower the number, the crisper the image. The dot pitch of color monitors for personal computers ranges from about 0.22 mm to 0.42 mm.


dot-matrix printer

A type of printer that produces characters and illustrations by striking pins against an ink ribbon to print closely spaced dots in the appropriate shape. Dot-matrix printers are inexpensive and relatively fast, but they do not produce high-quality output.

Dot-matrix printers vary in two important characteristics:

speed: Given in characters per second (cps), the speed can vary from about 50 to over 500 cps. Most dot-matrix printers offer different speeds depending on the quality of print desired.

print quality: Determined by the number of pins (the mechanisms that print the dots), it can vary from 9 to 24. The best dot-matrix printers (24 pins) can produce near letter-quality type, although you can still see a difference if you look closely.

In addition to these characteristics, you should also consider the noise factor. Compared to laser and ink-jet printers, dot-matrix printers are notorious for making a racket. Although the prices of laser and ink-jet printers are dropping rapidly, dot-matrix printers are still cheaper to operate. A page printed by a dot-matrix printer costs about a penny, whereas a laser-printed page costs two to three cents. In addition, most dot-matrix printers can print to multi-page forms (that is, carbon copies), something laser and ink-jet printers cannot do.


dots per inch

See dpi.


double click

Tapping a mouse button twice in rapid succession. Note that the second click must immediately follow the first, otherwise the program will interpret them as two separate clicks rather than one double click.

In Microsoft Windows and the Macintosh interface, you can use a double click to open files and applications. Both systems let you set the double-click speed (the longest acceptable interval between each click).


double precision

Refers to a type of floating-point number that has more precision (that is, more digits to the right of the decimal point) than a single-precision number. The term double precision is something of a misnomer because the precision is not really double. The word double derives from the fact that a double-precision number uses twice as many bits as a regular floating-point number. For example, if a single-precision number requires 32 bits, its double-precision counterpart will be 64 bits long.

The extra bits increase not only the precision but also the range of magnitudes that can be represented. The exact amount by which the precision and range of magnitudes are increased depends on what format the program is using to represent floating-point values. Most computers use a standard format known as the IEEE floating-point format.


double supertwist

See under supertwist.


double-density disk

A floppy disk that has twice the storage capacity of a single-density floppy. Single-density disks are now practically obsolete. Double-density 5¼-inch disks for PCs can hold 360K of data. Double-density 3½-inch disks can hold 720K.

Although high-density disk drives can format both high-density and double-density disks, double-density disks formatted by a high-density drive may not be readable by a double-density drive. Similarly, high-density drives may not be able to read disks that have been formatted by a double-density disk drive.


double-scan display

Same as dual-scan display.


double-sided disk

A floppy disk with both sides prepared for recording data. You can store twice as much data on a double-sided disk, but you need to use a double-sided disk drive. Nearly all modern disks and disk drives are double-sided.


double-speed CD-ROM

See under CD-ROM.


down

Not working. A computer system is said to be down when it is not available to users. This can occur because it is broken (that is, it has crashed), or because it has been made temporarily unavailable to users so that routine servicing can be performed.


download

To copy data (usually an entire file) from a main source to a peripheral device. The term is often used to describe the process of copying a file from an online service or bulletin board service (BBS) to one’s own computer. Downloading can also refer to copying a file from a network file server to a computer on the network.

In addition, the term is used to describe the process of loading a font into a laser printer. The font is first copied from a disk to the printer's local memory. A font that has been downloaded like this is called a soft font to distinguish it from the hard fonts that are permanently in the printer's memory.

The opposite of download is upload, which means to copy a file from your own computer to another computer.


downloadable font

Same as soft font.


downward compatible

Same as backward compatible.


DP

See data processing.


dpi

Abbreviation of dots per inch, which indicates the resolution of images. The more dots per inch, the higher the resolution. A common resolution for laser printers is 300 dots per inch. This means 300 dots across and 300 dots down, so there are 90,000 dots per square inch.


draft mode

A printing mode in which the printer prints text as fast as possible without regard to the print quality. Most dot-matrix printers support two modes: draft mode and either letter-quality (LQ) or near letter quality (NLQ) mode. In addition, many word processors support a draft mode in which they display and print pages without all the formatting detail specified for the document.


draft quality

Describes print whose quality is less than near letter quality. Most 9-pin dot-matrix printers produce draft-quality print.


drag

(1) In graphical user interfaces, drag refers to moving an icon or other image on a display screen. To drag an object across a display screen, you usually select the object with a mouse button (“grab” it) and then move the mouse while keeping the mouse button pressed down.

The term drag is also used more generally to refer to any operation in which the mouse button is held down while the mouse is moved. For example, you would drag the mouse to select a block of text.


drag-and-drop

Describes applications that allow you to drag objects to specific locations on the screen to perform actions on them. For example, in the Macintosh environment, you can drag a document to the trashcan icon to delete it. This is a classic case of drag-and-drop functionality.

When implemented well, drag-and-drop functionality is both faster and more intuitive than alternatives, such as selecting options from a menu or typing in commands.

Modern operating systems, including Windows and the Macintosh operating system, even allow you to drag and drop between applications. You can, for example, create a picture with a draw program, select it, and then drag it into a document that you are editing with a word processor.


DRAM

Pronounced dee-ram, DRAM stands for dynamic random access memory, a type of memory used in most personal computers.


draw program

A graphics program that enables you to draw pictures, then store the images in files, merge them into documents, and print them. Unlike paint programs, which represent images as bit maps, draw programs use vector graphics, which makes it easy to scale images to different sizes. In addition, graphics produced with a draw program have no inherent resolution. Rather, they can be represented at any resolution, which makes them ideal for high-resolution output.


drawing tablet

Same as digitizing tablet.


drive

Short for disk drive.


drive bay

An area of reserved space in a personal computer where hard or floppy disk drives (or tape drives) can be installed. The number of drive bays in a computer determines the total number of internal mass storage devices it can handle.


driver

A program that controls a device. Every device, whether it be a printer, disk drive, or keyboard, must have a driver program. Many drivers, such as the keyboard driver, come with the operating system. For other devices, you may need to load a new driver when you connect the device to your computer. In DOS systems, drivers are files with a .SYS extension. In Windows environments, drivers have a .DRV extension.

A driver acts like a translator between the device and programs that use the device. Each device has its own set of specialized commands that only its driver knows. In contrast, most programs access devices by using generic commands. The driver, therefore, accepts generic commands from a program and then translates them into specialized commands for the device.


drop cap

In desktop publishing, the first letter of a paragraph that is enlarged to “drop” down two or more lines, as in the next paragraph.

D	rop caps are used to make a page more visually interesting and to draw the reader’s eyes
to the beginning of a section.


drop-down menu

Same as pull-down menu.


DSP

Short for digital signal processing, which refers to manipulating analog information, such as sound or photographs that has been converted into a digital form. DSP also implies the use of a data compression technique.

When used as a noun, DSP stands for digital signal processor, a special type of coprocessor designed for performing the mathematics involved in DSP. Most DSPs are programmable, which means that they can be used for manipulating different types of information, including sound, images, and video.


DTP

See desktop publishing.


dual in-line package

See DIP.


dual supertwist

See under supertwist.


dual-scan display

A type of passive-matrix LCD display that provides faster refresh rates that conventional passive-matrix displays by refreshing the screen twice as fast. Dual-scan displays are not as sharp or bright as active-matrix displays, but they consume less power.


dumb terminal

A display monitor that has no processing capabilities. A dumb terminal is simply an output device that accepts data from the CPU. In contrast, a smart terminal is a monitor that has its own processor for special features, such as bold and blinking characters. Dumb terminals are not as fast as smart terminals, and they do not support as many display features, but they are adequate for most applications.


dummy

A placeholder. A dummy variable, for example, is a dummy variable that doesn’t contain any useful data, but it does reserve space that a real variable will use later.


dump

(n) The act of copying raw data from one place to another with little or no formatting for readability. Usually, dump refers to copying data from main memory to a display screen or a printer. Dumps are useful for diagnosing bugs. After a program fails, you can study the dump and analyze the contents of memory at the time of the failure. Dumps are usually output in a difficult-to-read form (that is, binary , octal, or hexadecimal), so a dump will not help you unless you know exactly what to look for.

(v) To output an image of computer memory.


duplex

Same as full duplex.


DVI

Abbreviation of Digital Video Interactive, a technology developed by General Electric that enables a computer to store and display moving video images like those on television. The most difficult aspect of displaying TV-like images on a computer is overcoming the fact that each frame requires an immense amount of storage. A single frame can require up to 2MB (megabytes) of storage. Televisions display 30 frames per second, which can quickly exhaust a computer's mass storage resources. It is also difficult to transfer so much data to a display screen at a rate of 30 frames per second.

DVI overcomes these problems by using specialized processors to compress and decompress the data. DVI is a hardware-only codec (compression/decompression)  technology. A competing hardware codec is MPEG. Intel has developed a software version of the DVI algorithms, which it markets under the name Indeo.


Dvorak keyboard

A keyboard designed for speed typing. The Dvorak keyboard was designed in the 1930s by August Dvorak, a professor of education, and his brother-in-law, William Dealy. Unlike the traditional QWERTY keyboard, the Dvorak keyboard is designed so that most words fall in the middle row of keys. In addition, common letter combinations are positioned in such a way that they can be typed quickly.

It has been estimated that in an average eight-hour day, a typist's hands travel 16 miles on a QWERTY keyboard, but only 1 mile on a Dvorak keyboard.

In addition to the standard Dvorak keyboard, there are two additional Dvorak keyboards, a left-handed and right-handed keyboard. These keyboards are designed for people who have only one hand for typing.


DXF

Abbreviation of Data Exchange File, a two-dimensional graphics file format supported by virtually all PC-based CAD products. It was created by AutoDesk for the AutoCAD system.


dynamic

Refers to actions that take place at the moment they are needed rather than in advance. For example, many programs perform dynamic memory allocation, which means that they do not reserve memory ahead of time, but seize sections of memory when needed. In general, such programs require less memory, although they may run a little more slowly.

The opposite of dynamic is static.


dynamic acceleration

A feature supported by some mice that causes the mouse resolution to depend on how fast the mouse is moved. When you move the mouse fast, the cursor moves proportionally further (the resolution is low). This is useful for jumping across the screen. Without this feature, you might need to sweep the mouse several times to move the cursor from one side of the display screen to the other. When you move the mouse slowly, the resolution increases to enable you to pinpoint specific pixels.

Dynamic resolution is also called ballistic tracking, automatic acceleration, variable acceleration, and dynamic acceleration.


Dynamic Data Exchange

See DDE.


dynamic RAM

A type of physical memory used in most personal computers. The term dynamic indicates that the memory must be constantly refreshed (reenergized) or it will lose its contents. RAM (random-access memory) is sometimes referred to as DRAM (pronounced dee-ram) to distinguish it from static RAM (SRAM). Static RAM is faster and more stable than dynamic RAM, but it requires more power and is more expensive.


dynamic variable

In programming, a dynamic variable is a variable whose address is determined when the program is run. In contrast, a static variable has memory reserved for it at compilation time.


e-mail

Short for electronic mail, the transmission of messages over communications networks. The messages can be notes entered from the keyboard or electronic files stored on disk. Most mainframes, minicomputers, and computer networks have an e-mail system. Some electronic-mail systems are confined to a single computer system or network, but others have gateways to other computer systems, enabling users to send electronic mail anywhere in the world. Companies that are fully computerized make extensive use of e-mail because it is fast, flexible, and reliable. In 1995, approximately 25 billion e-mail messages were sent.

Most e-mail systems include a rudimentary text editor for composing messages, but many allow you to edit your messages using any editor you want. You then send the message to the recipient by specifying the recipient's address. You can also send the same message to several users at once. This is called broadcasting.

Sent messages are stored in electronic mailboxes until the recipient fetches them. To see if you have any mail, you may have to check your electronic mailbox periodically, although many systems alert you when mail is received. After reading your mail, you can store it in a text file, forward it to other users, or delete it. Copies of memos can be printed out on a printer if you want a paper copy.

All online services and Internet Service Providers (ISPs) offer e-mail, and most also support gateways so that you can exchange mail with users of other systems. Usually, it takes only a few seconds or minutes for mail to arrive at its destination. This is a particularly effective way to communicate with a group because you can broadcast a message or document to everyone in the group at once.

Although different e-mail systems use different formats, there are some emerging standards that are making it possible for users on all systems to exchange messages. In the PC world, an important e-mail standard is MAPI. The CCITT standards organization has developed the X.400 standard, which attempts to provide a universal way of addressing messages. To date, though, the de facto addressing standard is the one used by the Internet system because almost all e-mail systems have an Internet gateway.

In recent years, the use of e-mail has exploded. By some estimates, there are now 25 million e-mail users sending 15 billion messages per year.


EBCDIC

Abbreviation of Extended Binary-Coded Decimal Interchange Code. Pronounced eb-see-dik, EBCDIC is an IBM code for representing characters as numbers. Although it is widely used on large IBM computers, most other computers, including PCs and Macintoshes, use ASCII codes.


ECP

Short for Extended Capabilities Port, a parallel-port standard for PCs that supports bi-directional communication between the PC  and attached devices (such as a printer). ECP is about 10 times faster than the older Centronics standard.

Another modern parallel port for PCs that offers similar performance is the EPP (Enhanced Parallel Port).


edge connector

The part of a printed circuit board that plugs into a computer or device. The edge connector generally has a row of broad metallic tracks that provide the electrical connection.


editor

Sometimes called text editor, a program that enables you to create and edit text files. There are many different types of editors, but they all fall into two general categories:

line editors: A primitive form of editor that requires you to specify a specific line of text before you can make changes to it.

screen-oriented editors: Also called full-screen editors, these editors enable you to modify any text that appears on the display screen by moving the cursor to the desired location.

The distinction between editors and word processors is not clear-cut, but in general, word processors provide many more formatting features.


EDO DRAM

Short for Enhanced Data Output Dynamic Access Random Memory, a type of DRAM that is 30 to 50 percent faster than conventional DRAM. Unlike conventional DRAM, EDO DRAM does not need to be refreshed between each access, so its cycle time is much shorter.


EEMS

Abbreviation of Enhanced Expanded Memory Specification, an enhanced version of the original EMS, which enables DOS applications to use more than 1MB (megabyte) of memory. EEMS was developed by AST, Quadram, and Ashton-Tate to improve the performance of the original version of EMS. Subsequently, Lotus, Intel, and Microsoft developed the LIM 4.0 version of EMS, which supports both the original EMS and EEMS.


EEPROM

Acronym for electrically erasable programmable read-only memory. Pronounced double-ee-prom, an EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM.

A special type of EEPROM, referred to as flash memory or flash EEPROM, can be rewritten while it is in the computer rather than requiring a special device called a PROM reader.


EGA

Abbreviation of enhanced graphics adapter, a graphics display system for PCs introduced by IBM in 1984. EGA supports 16 colors from a palette of 64 and provides a resolution of 640 by 350. This is better than CGA but not as good as VGA.


EIA (Electronics Industry Association) interface

Same as RS-232C.


EIDE

Short for Enhanced IDE, a new version of the IDE mass storage device interface standard developed by Western Digital Corporation. It supports data rates of between 11.1 and 13.3MB (megabytes) per second, about three to four times faster than the old IDE standard. In addition, it can support mass storage devices of up to 8.4 gigabytes, whereas the old standard was limited to 528MB. Because of its lower cost, enhanced IDE is expected to replace SCSI in many areas. Although currently implemented only on PCs, Apple has announced that it will support EIDE in future versions of the Macintosh.

EIDE is sometimes referred to as Fast ATA, or Fast IDE, which is essentially the same standard, developed and promoted by Seagate Technologies.


EISA

Acronym for Extended Industry Standard Architecture, a bus architecture designed for PCs using an Intel 80386, 80486, or Pentium microprocessor. EISA buses are 32 bits wide and support multiprocessing.

The EISA bus was designed by nine IBM competitors (sometimes called the Gang of Nine): AST Research, Compaq Computer, Epson, Hewlett-Packard, NEC Information Systems, Olivetti, Tandy, WYSE, and Zenith Data Systems. They designed the architecture to compete with IBM's own high-speed bus architecture called the Micro Channel architecture (MCA).

The principal difference between EISA and MCA is that EISA is backward compatible with the ISA bus (also called the AT bus), while MCA is not. This means that computers with an EISA bus can use new EISA expansion cards as well as old AT expansion cards. Computers with an MCA bus can use only MCA expansion cards.

EISA and MCA are not compatible with each other. This means that the type of bus in your computer determines which expansion cards you can install.

Neither EISA nor MCA has been very successful. Instead, a new technology called local bus is being used in combination with the old ISA bus. There are two competing local bus standards—PCI and VL-bus—but it now seems that PCI will become the de facto standard for PCs, and possibly for Macintoshes as well.


ELD

See electroluminescent display.


electrically erasable programmable read-only memory

See EEPROM.


electroluminescent display (ELD)

A technology used to produce a very thin display screen, called a flat-panel display, used in some portable computers. An ELD works by sandwiching a thin film of phosphorescent substance between two plates. One plate is coated with vertical wires and the other with horizontal wires, forming a grid. When an electrical current is passed through a horizontal and vertical wire, the phosphorescent film at the intersection glows, creating a point of light, or pixel.

Other types of flat-panel displays include LCD displays and gas-plasma displays, both of which are more common than ELDs.


electronic mail

See under e-mail.


electronic publishing

Publishing information in an electronic form. This includes publishing CD-ROMs as well as making information available through online services.


elevator

Same as scroll box. See under scroll bar.


ELF emission

ELF stands for extremely low frequency, and ELF emissions are magnetic fields generated by common electrical appliances. There is considerable debate about whether ELF emissions from computer monitors pose a threat. Some European countries have adopted regulations controlling the amount of allowable emission. The most well-know regulation is Sweden’s MPR II standard. You can play it safe by buying MPR II-compliant monitors.


embedded command

In word processing, an embedded command is a sequence of special characters inserted into a document that affects the formatting of the document when it is printed. For example, when you change fonts in a word processor (by specifying bold type), the word processor inserts an embedded command that causes the printer to change fonts. Embedded commands can also control the display screen, causing it to display blinking characters or produce other special effects.

Embedded commands are usually invisible when you edit a file, but many word processors support a special mode that lets you see these commands.


embedded object

An object created with one application and embedded into a document created by another application. Embedding the object, rather than simply inserting or pasting it, ensures that the object retains its original format. In fact, you can modify the embedded object with the original program. In Windows environments, embedding objects is made possible by a technology called OLE.


emoticon

Short for emotion icon, a small icon composed of punctuation characters that indicates how an e-mail message should be interpreted (that is, the writer’s mood). For example, a :-) smiley indicates that the message is meant as a joke and shouldn’t be taken seriously.


EMS

Abbreviation of Expanded Memory Specification.


emulation

Refers to the ability of a program or device to imitate another program or device. Many printers, for example, are designed to emulate Hewlett-Packard LaserJet printers because so much software is written for the HP printers. By emulating an HP printer, a printer can work with any software written for a real HP printer. Emulation tricks the software into believing that a device is really some other device.

Communications software packages often include terminal emulation drivers. This enables your PC to emulate a particular type of terminal so that you can log on to a mainframe.

It is also possible for a computer to emulate another type of computer. For example, there are programs that enable an Apple Macintosh to emulate a PC.


Encapsulated PostScript

See EPS.


encryption

The translation of data into a secret code. Encryption is the most effective way to achieve data security. To read an encrypted file, you must have access to a secret key or password that enables you to decrypt it.


End key

A special cursor control key on PC keyboards and Macintosh extended keyboards. The End key has different meanings depending on which program is running. For example, it might move the cursor to the end of the line, the end of the page, or the end of the file.


end of file

See EOF.


end of line

See EOL mark.


end user

The final or ultimate user of a computer system. The end user is the individual who uses the product after it has been fully developed and marketed. The term is useful because it distinguishes two classes of users, users who require a bug-free and finished product (end users), and users who may use the same product for development purposes. The term end user usually implies an individual with a relatively low level of computer expertise. Unless you are a programmer or engineer, you are almost certainly an end user.


Energy Star

A set of guidelines issued by the U.S. Environmental Protection Agency to minimize energy consumption. Energy Star devices can detect when they are idle and switch to a low-energy mode in which they consume 30 watts or less.


Enhanced Data Output DRAM

See EDO DRAM.


Enhanced Expanded Memory Specification

See EEMS.


enhanced graphics adapter

See EGA.


Enhanced IDE

See under EIDE.


Enhanced Keyboard

(1) A 101- or 102-key keyboard from IBM that supersedes the keyboard for the PC/AT computer. The most significant difference between the enhanced keyboard and previous models is that the enhanced keyboard has a row of 12 function keys at the top instead of 10 function keys grouped on the left side of the keyboard. Nearly all PCs made today come with an Enhanced Keyboard.

(2) For Macintoshes, see under extended keyboard.


Enhanced Parallel Port

See EPP.


Enhanced Small Device Interface

See ESDI.


Enter key

A key that moves the cursor (or insertion point) to the beginning of the next line, or returns control to whatever program is currently running. After a program requests information from you (by displaying a prompt), it will usually not respond to your input until you have pressed the Enter or Return key. This allows you to correct typing mistakes or to reconsider your entry before it is too late. In many applications, pressing the Enter key moves the cursor to the next field. In graphical user interfaces, pressing Enter activates the currently selected button or option.


environment

(1) The state of a computer, usually determined by which programs are running and basic hardware and software characteristics. For example, when one speaks of running a program in a UNIX environment, it means running a program on a computer that has the UNIX operating system.

One ingredient of an environment, therefore, is the operating system. But operating systems include a number of different parameters. For example, many operating systems allow you to choose your command prompt or a default command path. All these parameters taken together constitute the environment.

Another term for environment in this sense is platform.

(2) In DOS systems, the environment is an area in memory that the operating system and other programs use to store various types of miscellaneous information. For example, your word processor may use the environment area to store the location of backup files. You can view or modify the environment with the SET command.


EO

See erasable optical disk.


EOF mark

Short for end-of-file mark, a special character or sequence of characters that marks the end of a file. Operating systems need to keep track of where every file ends. There are two techniques for doing this: One is to put a special end-of-file mark at the end of each file. The other is to keep track of how many characters are in the file.

In many operating systems, including DOS and OS/2, the end-of-file mark is CTRL-Z. In UNIX, the end-of-file mark is CTRL-D.


EOL mark

Short for end-of-line mark, a special character or sequence of characters that marks the end of a line. For many programs, the EOL character is CTRL-M (carriage return) or CTRL-J (new line). End-of-line can also be abbreviated EOLN.


EPP

Short for Enhanced Parallel Port, a parallel port standard for PCs that supports bi-directional communication between the PC  and attached devices (such as a printer). EPP is about 10 times faster than the older Centronics standard.

Another modern parallel port for PCs that offers similar performance is the ECP (Extended Capabilities Port).


EPROM

Acronym for erasable programmable read-only memory, and pronounced ee-prom, EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. To write to and erase an EPROM, you need a special device called a PROM programmer or PROM burner.

An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROMs are used widely in personal computers because they enable the manufacturer to change the contents of the PROM before the computer is actually shipped. This means that bugs can be removed and new versions installed shortly before delivery.


EPS

Abbreviation of Encapsulated PostScript. Pronounced as separate letters, EPS is the graphics file format used by the PostScript language.

EPS files can be either binary  or ASCII. The term EPS usually implies that the file contains a bit-mapped representation of the graphics for display purposes. In contrast, PostScript files include only the PostScript commands for printing the graphic.


erasable optical disk

A type of optical disk that can be erased and loaded with new data, just like magnetic disks. In contrast, most optical disks, called CD-ROMs, are read-only.

Although the technology is still young, erasable optical disks seem destined to become the future medium of choice. A single 5¼-inch optical disk can store 650 megabytes of data, about 1,000 times more than a typical floppy disk. And unlike hard disks, optical disks are portable.

The data-access speed of optical disks varies considerably, from about 20 to 200 milliseconds. Though comparable to floppy disks, they are not yet as fast as magnetic hard disk drives.


erasable programmable read-only memory

See EPROM.


ergonomics

The science concerned with designing safe and comfortable machines for humans. For example, one branch of ergonomics deals with designing furniture that avoids causing backaches and muscle cramps. In the computer field, ergonomics plays an important role in the design of monitors and keyboards.

Another term for ergonomics is human engineering.


error detection

In communications, error detection refers to a class of techniques for detecting garbled messages. Two of the simplest and most common techniques are called checksum and CRC. More sophisticated strategies include MNP and CCITT V.42.


ESC

Short for Escape key. For example, ESC-Q means press the Escape key and then the Q key.


escape character

A special character that can have many different functions. It is often used to abort the current  command and return to a previous place in the program. It is also used to send special instructions to printers and other devices. An escape character is generated with the Escape key, a special key that exists on most computer keyboards.

When the escape character is combined with other characters, it is called an escape sequence.


Escape key

A key on computer keyboards, usually labeled Esc. In DOS and Windows environments, pressing the Escape key usually cancels or aborts the current operation.


escape sequence

A sequence of special characters that sends a command to a device or program. Typically, an escape sequence begins with an escape character, but this is not universally true.


ESDI

Abbreviation of Enhanced Small Device Interface, an interface standard developed by a consortium of the leading personal computer manufacturers for connecting disk drives to PCs. ESDI is two to three times faster than the older ST-506 standard. To use an ESDI drive, your computer must have an ESDI controller.

Introduced in the early 80s, ESDI is already obsolete. Instead, modern computers use a SCSI, IDE, or EIDE interface.


Ethernet

A local-area network (LAN) protocol developed by Xerox Corporation in cooperation with DEC and Intel in 1976. Ethernet uses a bus topology and supports data transfer rates of 10 megabits (10 million bits) per second. The Ethernet specification served as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers. It is one of the most widely implemented LAN standards.

A new version of Ethernet, called 100BaseX (or Fast Ethernet), supports data transfer rates of 100 megabits per second.


even header

In word processing, a header that appears only on even-numbered pages.


even parity

Refers to the parity-checking mode in which each set of transmitted bits must have an even number of set bits. The parity checking system ensures even parity by setting the extra parity bit if necessary.


event

An action or occurrence detected by a program. Events can be user actions, such as clicking a mouse button or pressing a key, or system occurrences, such as running out of memory. Most modern applications, particularly those that run in Macintosh and Windows environments, are said to be event-driven, because they are designed to respond to events.


exclusive OR

A Boolean operator that returns a value of TRUE only if both its operands have different values. Contrast with the inclusive OR operator, which returns a value of TRUE if either of its operands is TRUE.


EXE file

Pronounced ee-ex-ee file, in DOS and Windows systems, an EXE file is an executable file with an .EXE extension.


executable file

A file in a format that the computer can directly execute. Unlike source files, executable files cannot be read by humans. To transform a source file into an executable file, you need to pass it through a compiler or assembler.

In DOS systems, executable files have either a .COM or .EXE extension and are called COM files and EXE files, respectively.


execute

Same as run. Execute means to perform an action, as in executing a program or a command.


expanded memory

Also known as EMS (Expanded Memory Specification), expanded memory is a technique for utilizing more than 1MB (megabyte) of main memory in DOS-based computers. The limit of 1MB is built into the DOS operating system. The upper 384K is reserved for special purposes, leaving just 640K of conventional memory for programs.

There are several versions of EMS. The original versions, called EMS 3.0 and 3.2, enable programs to use an additional 8MB of memory, but for data only. An improved version developed by AST, Quadram and Ashton-Tate is known as EEMS (Extended EMS) . EEMS enables programs to use extra memory for code as well as for data. The most recent version of EMS (created in 1987) is known as EMS 4.0 or LIM 4.0, LIM being the initials of the three companies that developed the specification: Lotus, Intel, and Microsoft. EMS 4.0 raises the available amount of memory to 32MB.

Until the release of Microsoft Windows 3.0 in 1990, expanded memory was the preferred way to add memory to a PC. The alternative method, called extended memory, was less flexible and could be used only by special programs such as RAM disks. Windows 3.0 and all later versions of Windows, however, contain an extended memory manager that enables programs to use extended memory without interfering with one another. In addition, Windows can simulate expanded memory for those programs that need it.


expansion board

A printed circuit board that you can insert into a computer to give it added capabilities. For example, all of the following are expansion boards:

•	video adapters

•	graphics accelerators

•	sound cards

•	accelerator boards

•	internal modems

Expansion boards for PCs can be half-size (also half-length) or full-size (also full-length). Most PCs have slots for each type of board. A half-size board is sometimes called an 8-bit board because it can transmit only 8 bits at a time. A full-size board is called a 16-bit board. In addition, some expansion boards are designed to operate with a local bus, such as PCI.

Expansion boards are also called adapters, cards, add-ins, and add-ons.


expansion bus

A collection of wires and protocols that allows the expansion of a computer by inserting printed circuit boards (expansion boards). Traditionally, PCs have utilized an expansion bus called the ISA bus. In recent years, however, the ISA bus has become a bottleneck, and there are now several competing standards for a new PC expansion bus. These include EISA, PCI, and VL-Bus.


expansion card

Same as expansion board.


expansion slot

An opening in a computer where a circuit board can be inserted to add new capabilities to the computer. Nearly all personal computers except portables contain expansion slots for adding more memory, graphics capabilities, and support for special devices. The boards inserted into the expansion slots are called expansion boards, expansion cards, cards, add-ins, and add-ons.

Expansion slots for PCs come in two basic sizes: half- and full-size. Half-size slots are also called 8-bit slots because they can transfer 8 bits at a time. Full-size slots are sometimes called 16-bit slots. In addition, many modern computers include local-bus slots for expansion boards that connect directly to the machine’s local bus.


expert system

A computer application that performs a task that would otherwise be performed by a human expert. For example, there are expert systems that can diagnose human illnesses, make financial forecasts, and schedule routes for delivery vehicles. Some expert systems are designed to take the place of human experts, while others are designed to aid them.

Expert systems are part of a general category of computer applications known as artificial intelligence. To design an expert system, one needs a knowledge engineer, an individual who studies how human experts make decisions and translates the rules into terms that a computer can understand.


exploded view

A picture or diagram that shows the components of an object slightly separated, as if there had been a neat explosion in the middle of the object. Many spreadsheet applications can automatically create exploded diagrams such as exploded pie charts.


export

To format data in such a way that it can be used by another application. An application that can export data can create a file in a format that another application understands, enabling the two programs to share the same data. The two programs might be different types of word processors, or one could be a word processor while the other could be a database management system.

The flip side of exporting is importing. Importing refers to the ability of an application to read and use data produced by a different application. Exporting implies that the sending application reformats the data for the receiving application, whereas importing implies that the receiving application does the reformatting.


expression

In programming, an expression is any legal combination of symbols that represents a value. Each programming language and application has its own rules for what is legal and illegal. For example, in the C language x+5 is an expression, as is the character string “MONKEYS.”

Every expression consists of at least one operand and can have one or more operators. Operands are values, whereas operators are symbols that represent particular actions. In the expression

x + 5

x and 5 are operands, and + is an operator.

Expressions are used in programming languages, database systems, and spreadsheet applications. For example, in database systems, you use expressions to specify which information you want to see. These types of expressions are called queries.

Expressions are often classified by the type of value that they represent. For example:

Boolean expressions: Evaluate to either TRUE or FALSE

integer expressions: Evaluate to whole numbers, like 3 or 100

Floating-point expressions: Evaluate to real numbers, like 3.141 or -0.005

String expressions: Evaluate to character strings


extended ASCII

A set of codes that extends the basic ASCII set. The basic ASCII set uses 7 bits for each character, giving it a total of 128 unique symbols. The extended ASCII character set uses 8 bits, which gives it an additional 128 characters. The extra characters represent characters from foreign languages and special symbols for drawing pictures.


Extended Binary-Coded Decimal Interchange Code

See EBCDIC.


Extended Capabilities Port

See ECP.


extended graphics array

See XGA.


Extended Industry Standard Architecture

See EISA


extended keyboard

A keyboard for Macintosh computers that contains up to 15 function keys above the  alphanumeric keys, and a numeric keypad. It is sometimes called an enhanced keyboard because of its similarity to the PC enhanced keyboard.


extended memory

Memory above and beyond the standard 1MB (megabyte) of main memory that DOS supports. Extended memory is only available in PCs with an Intel 80286 or later microprocessor.

Two types of memory can be added to a PC to increase memory beyond 1MB: expanded memory and extended memory. Expanded memory conforms to a published standard called EMS that enables DOS programs to take advantage of it. Extended memory, on the other hand, is not configured in any special manner and is therefore unavailable to most DOS programs. However, MS-Windows and OS/2 can use extended memory.


Extended Memory Specification

See XMS.


extended VGA

See SVGA.


extension

(1) An extra feature added to a standard programming language or system.

(2) In DOS and some other operating systems, one or several letters at the end of a filename. Filename extensions usually follow a period (dot) and indicate the type of information stored in the file. For example, in the filename EDIT.COM, the extension is COM, which indicates that the file is a command file. (Depending on the operating system, the punctuation separating the extension from the rest of the filename may or may not be considered part of the extension itself.)

(3) In Macintosh environments, a program that extends the system’s capabilities. When they reside in the Extensions folder, extensions are loaded into memory when the system starts. On older Macs (System 6 and earlier), extensions were called inits.


external cache

Same as secondary cache.


external command

In DOS systems, any command that does not reside in the COMMAND.COM file. This includes all other COM files, as well as EXE and BAT files. Commands in the COMMAND.COM file are called internal commands.


external modem

A modem that resides in a self-contained box outside the computer system. Contrast with an internal modem, which resides on a printed circuit board inserted into the computer.

External modems tend to be slightly more expensive than internal modems. Many experts consider them superior because they contain lights that indicate how the modem is functioning. In addition, they can easily be moved from one computer to another.


extremely low-frequency (ELF) emission

See ELF emission.


F1, F2...F15

The names of the function keys. See under function keys.


facsimile machine

See fax machine.


FAQ

Pronounced fak, and short for frequently asked questions, a FAQ is a document that answers questions about some technical topic. Frequently, FAQs are formatted as help files or hypertext documents.


Fast AT Attachment (ATA)

See under EIDE.


Fast Ethernet

See under Ethernet.


fast IDE

Short for Fast AT Attachment (ATA). See under EIDE.


FAT

See file allocation table.


fatal error

An error that causes a program to abort. Sometimes a fatal error returns you to the operating system. When a fatal error occurs, you may lose whatever data the program was currently processing.


fault tolerance

The ability of a system to respond gracefully to an unexpected hardware or software failure. There are many levels of fault tolerance, the lowest being the ability to continue operation in the event of a power failure. Many fault-tolerant computer systems mirror all operations—that is, every operation is performed on two or more duplicate systems, so if one fails the other can take over.


fax

(v) To send a document via a fax machine.

(n) (1) A document that has been sent, or is about to be sent, via a fax machine.

(2) Short for Facsimile machine.


fax board

See fax modem.


fax machine

Abbreviation of facsimile machine, a fax machine is a device that can send or receive pictures and text over a telephone line. Fax machines work by digitizing an image—dividing it into a grid of dots. Each dot is either on or off, depending on whether it is black or white. Electronically, each dot is represented by a bit that has a value of either 0 (off) or 1 (on). In this way, the fax machine translates a picture into a series of zeros and ones (called a bit map) that can be transmitted like normal computer data. On the receiving side, a fax machine reads the incoming data, translates the zeros and ones back into dots, and reprints the picture.

The idea of fax machines has been around since 1842, when Alexander Bain invented a machine capable of receiving signals from a telegraph wire and translating them into images on paper. In 1850, a London inventor named F. C. Blakewell received a patent for a similar machine, which he called a copying telegraph.

But while the idea of fax machines has existed since the 1800s, fax machines did not become popular until the mid 1980s. The spark igniting the fax revolution was the adoption in 1983 of a standard protocol for sending faxes at rates of 9,600 bps. The standard was created by the CCITT standards organization and is known as the Group 3 standard. Now, faxes are commonplace in offices of all sizes. They provide an inexpensive, fast, and reliable method for transmitting correspondence, contracts, résumés, handwritten notes, and illustrations.

A fax machine consists of an optical scanner for digitizing images on paper, a printer for printing incoming fax messages, and a telephone for making the connection. The optical scanner generally does not offer the same quality of resolution as stand-alone scanners. Most printers on fax machines are thermal, which means they require a special kind of paper.

All fax machines conform to the CCITT Group 3 protocol. (There is a new protocol called Group 4, but it requires ISDN lines.) The Group 3 protocol supports two classes of resolution: 203 by 98 dpi and 203 by 196 dpi. The protocol also specifies a data-compression technique and a maximum transmission speed of 9,600 bps.

Some of the features that differentiate one fax machine from another include the following:

speed: fax machines transmit data at different rates, from 4,800 bps to 28,800 bps. A 9,600-bps fax machine typically requires 10 to 20 seconds to transmit one page.

printer type: Most fax machines use a thermal printer that requires special paper that tends to turn yellow or brown after a period. More expensive fax machines have printers that can print on regular bond paper.

paper size: The thermal paper used in most fax machines comes in two basic sizes: 8.5-inches wide and 10.1-inches wide. Some machines accept only the narrow-sized paper.

paper cutter: Most fax machines include a paper cutter because the thermal paper that most fax machines use comes in rolls. The least expensive models and portable faxes, however, may not include a paper cutter.

paper feed: Most fax machines have paper feeds so that you can send multiple-page documents without manually feeding each page into the machine.

autodialing: fax machines come with a variety of dialing features. Some enable you to program the fax to send a document at a future time so that you can take advantage of the lowest telephone rates.

As an alternative to stand-alone fax machines, you can also put together a fax system by purchasing separately a fax modem and an optical scanner. You may not even need the optical scanner if the documents you want to send are already in electronic form.


fax modem

A device you can attach to a personal computer that enables you to transmit (and sometimes receive) electronic documents as faxes. A fax modem is like a regular modem except that it is designed to transmit documents to a fax machine or to another fax modem. Some, but not all, fax modems do double duty as regular modems. As with regular modems, fax modems can be either internal or external. Internal fax modems are often called fax boards.

Documents sent through a fax modem must already be in an electronic form (that is, in a disk file), and the documents you receive are likewise stored in files on your disk. To create fax documents from images on paper, you need an optical scanner.

Fax modems come with communications software similar to communications software for regular modems. This software can give the fax modem many capabilities that are not available with stand-alone fax machines. For example, you can broadcast a fax document to several sites at once. In addition, fax modems offer the following advantages over fax machines:

price: fax modems are less expensive. In addition, they require less maintenance because there are no moving parts. However, if you need to purchase an optical scanner in addition to the fax modem, there is no price advantage.

convenience: fax modems are more convenient if the documents you want to send are already in electronic form. With a fax machine, you would first need to print the document. A fax modem lets you send it directly.

speed: fax modems can almost always transmit documents at the maximum speed of 9,600 bps, whereas not all fax machines support such high data-transmission rates.

image quality: The image quality of documents transmitted by fax modems is usually superior because the documents remain in electronic form.

The principal disadvantage of fax modems is that you cannot fax paper documents unless you buy a separate optical scanner, which eliminates any cost and convenience advantages of fax modems. Another problem with fax modems is that each document you receive requires an enormous amount of disk storage (about 100K per page). Not only does this eat up disk storage, but it takes a long time to print such files.


FCC

Abbreviation of Federal Communications Commission. Among other duties, the FCC is responsible for rating personal computers and other equipment as either Class A or Class B. The ratings indicate how much radiation a personal computer emits. Almost all personal computers satisfy Class A requirements, which means they are suitable for office use. Class B machines, which are suitable for use anywhere (including the home), must pass more stringent tests. Class B indicates that the machine's radio frequency (RF) emissions are so low that they do not interfere with other devices such as radios and TVs.


FDDI

Abbreviation of Fiber-Optic Digital Device Interface, a set of ANSI protocols for sending digital data over fiber optic cable. FDDI networks are token-passing networks, and support data rates of up to 100 Mbps (100 million bits) per second. FDDI networks are typically used as backbones for wide-area networks.

An extension to FDDI, called FDDI-2, supports the transmission of voice and video information as well as data. Another variation of FDDI, called FDDI Full Duplex Technology (FFDT) uses the same network infrastructure but can potentially support data rates up to 200 Mbps.


FDHD

Short for floppy drive, high density, and pronounced fud-hud. FDHD refers to 3½-inch disk drives for Macintosh computers that can accept double-density or high-density 3½-inch floppy disks. FDHDs can also read DOS-formatted floppy disks, which enables Macintosh computers and PCs to share data. FDHD drives are often called SuperDrives.


feathering

In desktop publishing, feathering is the process of adding space between all lines on a page or in a column to force vertical justification.


feature

A notable property of a device or software application. Many analysts bemoan the advent of featurism—the seemingly endless addition of more and more features onto what was once a simple application. One of the principal challenges of modern applications is to offer a multitude of features without making the application complex.


Federal Communications Commission

See FCC.


female connector

See under connector.


FF

See form feed.


Fiber Optic Digital Device Interface

See FDDI.


fiber optics

A technology that uses glass (or plastic) threads (fibers) to transmit data. A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages at close to the speed of light.

Fiber optics has several advantages over traditional metal communications lines:

•	Fiber optic cables have a much greater bandwidth than metal cables. This means that they can carry more data.

•	Fiber optic cables are less susceptible than metal cables to interference.

•	Fiber optic cables are much thinner and lighter than metal wires.

•	Data can be transmitted digitally (the natural form for computer data) rather than analogically.

The main disadvantage of fiber optics is that the cables are expensive to install. In addition, they are more fragile than wire and are difficult to split.

Fiber optics is a particularly popular technology for local-area networks. In addition, telephone companies are steadily replacing traditional telephone lines with fiber optic cables. In the future, almost all communications will employ fiber optics.


field

(1) A space allocated for a particular item of information. A tax form, for example, contains a number of fields: one for your name, one for your Social Security number, one for your income, and so on. In database systems, fields are the smallest units of information you can access. In spreadsheets, fields are called cells.

Most fields have certain attributes associated with them. For example, some fields are numeric whereas others are textual, some are long, while others are short. In addition, every field has a name, called the field name.

In database management systems, a field can be required, optional, or calculated. A required field is one in which you must enter data, while an optional field is one you may leave blank. A calculated field is one whose value is derived from some formula involving other fields. You do not enter data into a calculated field; the system automatically determines the correct value.

A collection of fields is called a record.

(2) The phrase in the field refers to any geographical location other than the factory or office where a product was created. Similarly, a field representative is an employee who represents a company in distant locations.


file

A collection of data or information that has a name, called the filename. Almost all information stored in a computer must be in a file. There are many different types of files: data files, text files, program files, directory files, and so on. Different types of files store different types of information. For example, program files store programs, whereas text files store text.


file allocation table (FAT)

A table that the operating system uses to locate files on a disk. Due to fragmentation, a file may be divided into many sections that are scattered around the disk. The FAT keeps track of all these pieces.

In DOS systems, FATs are stored in hidden files, called FAT files.


file attribute

See under attribute.


file compression

See under data compression and packed file.


file defragmentation

See under fragmentation.


file extension

See extension.


file format

A format for encoding information in a file. Each different type of file has a different file format. The file format specifies first whether the file is a binary or ASCII file, and second, how the information is organized.


file fragmentation

See fragmentation.


file locking

See under lock.


file management system

The system that an operating system or program uses to organize and keep track of files. For example, a hierarchical file system is one that uses directories to organize files into a tree structure.

Although the operating system provides its own file management system, you can buy separate file management systems. These systems interact smoothly with the operating system but provide more features, such as improved backup procedures and stricter file protection.


file server

See under server.


file system

Same as file management system.


File Transfer Program

See FTP.


filename

The name of a file. All files have names. Different operating systems impose different restrictions on filenames. Most operating systems, for example, prohibit the use of certain characters in a filename and impose a limit on the length of a filename. In addition, many systems, including DOS and UNIX, allow a filename extension that consists of one or more characters following the proper filename. The filename extension usually indicates what type of file it is.

Within a single directory, filenames must be unique. However, two files in different directories may have the same name. Some operating systems, such as UNIX and the Macintosh operating system, allow a file to have more than one name, called an alias.


filename extension

See extension.


fill

(1) In graphics applications, to paint the inside of an enclosed object. Typically, you can choose a color and pattern, and then paint the object with a fill tool. The area that is painted is called the fill area.

(2) In spreadsheet applications, to copy the contents of one cell to an entire range of cells—that is, to fill the range with a formula or value.


filter

(1) A program that accepts a certain type of data as input, transforms it in some manner, and then outputs the transformed data. For example, a program that sorts names is a filter because it accepts the names in unsorted order, sorts them, and then outputs the sorted names.

Utilities that allow you to import or export data are also sometimes called filters.

(2) A pattern through which data is passed. Only data that matches the pattern is allowed to pass through the filter.

(3) In paint programs and image editors, a filter is an effect that can be applied to a bit map. Some filters mimic conventional photographic filters, but many transform images in unusual ways. A pointillism filter, for example, can make a digitized photograph look like a pointillistic painting.


Finder

The desktop management and file management system for Apple Macintosh computers. In addition to managing files and disks, the Finder is responsible for managing the Clipboard and Scrapbook and all desktop icons and windows.


firewall

A system designed to prevent unauthorized access% to or from a private network%.  Firewalls can be implemented in both hardware% and software%, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet% users from accessing private networks connected to the Internet, especially intranets.  All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security% criteria.

A firewall is considered a first line of defense in protecting private information. For greater security, data% can be encrypted%.


firmware

Software (programs or data) that has been permanently written onto read-only memory (ROM). Firmware is a combination of software and hardware. ROMs and PROMs that have data or programs recorded on them are firmware.


fixed disk

Same as hard disk.


fixed length

Having a set length that never varies. In database systems, a field can have a fixed or a variable length. A variable-length field is one whose length can be different in each record, depending on what data is stored in the field.

The terms fixed length and variable length can also refer to the entire record. A fixed-length record is one in which every field has a fixed length. A variable-length record has at least one variable-length field.


fixed pitch

Refers to fonts in which every character has the same width. Most typewriters and inexpensive printers use fixed-pitch fonts. Newspapers, magazines, and books, however, usually use proportional fonts, in which different characters have different widths.

The use of a fixed-pitch font is called monospacing.


fixed width

Same as fixed pitch.


fixed-frequency monitor

A monitor that can only accept signals in one frequency range. In contrast, multiscanning monitors automatically adjust themselves to the frequency at which data is being sent.


flag

(n) (1) A software or hardware mark that signals a particular condition or status. A flag is like a switch that can be either on or off. The flag is said to be set when it is turned on.

(2) A special mark indicating that a piece of data is unusual. For example, a record might contain an error flag to indicate that the record consists of unusual, probably incorrect, data.

(v) To mark an object to indicate that a particular event  has occurred or that the object marked is unusual is some way.


flame

(n) A searing e-mail message in which the writer attacks another e-mail participant in overly harsh, and often personal, terms. Flames are an unfortunate, but inevitable, element of unmoderated conferences.

(v) To post a flame.


flash BIOS

See under BIOS.


flash memory

A special type of EEPROM that can be erased and reprogrammed inside a computer. Unlike conventional EEPROM, which requires a special device called a PROM reader that exposes the memory to higher-than-normal voltages, flash memory can be erased using the normal voltages inside a PC.

Many modern PCs have their BIOS stored on a flash memory chip so that it can easily be updated if necessary. Such a BIOS is sometimes called a flash BIOS.


flash ROM

Same as flash memory.


flat screen

Same as flat-panel display.


flat technology monitor

Often abbreviated as FTM, flat technology monitors are monitors that have a flat display screen to reduce glare. Conventional display screens are curved, which makes them more susceptible to reflections from external light sources.

Do not confuse flat technology monitors with flat-panel displays. Flat-panel displays are the display screens used in laptops and other portable computers.


flat-file database

A relatively simple database system in which each database is contained in a single table. In contrast, relational database systems can use multiple tables to store information, and each table can have a different record format. Relational systems are more suitable for large applications, but flat databases are adequate for many small applications.


flat-panel display

A very thin display screen used in portable computers. Nearly all modern flat-panel displays use LCD technologies. Most LCD screens are backlit to make them easier to read in bright environments.


flatbed scanner

A type of optical scanner that consists of a flat surface on which you lay documents to be scanned. Flatbed scanners are particularly effective for bound documents.


flicker

See screen flicker.


floating

In graphical user interfaces, floating refers to application elements that you can move to different places. Many applications support floating toolbars, which are collections of icons that represent tools. By moving them wherever you want on the screen, you can create your own customized working environment. In addition to toolbars, many graphics programs support floating palettes.


floating-point number

A real number (that is, a number that can contain a fractional part). The following are floating-point numbers:

3.0

-111.5

½

3E-5

The last example is a computer shorthand for scientific notation. It means 3*10-5 (or 10 to the negative 5th power multiplied by 3).

In essence, computers are integer machines and are capable of representing real numbers only by using complex codes. The most popular code for representing real numbers is called the IEEE Floating-Point Standard.

The term floating point is derived from the fact that there is no fixed number of digits before and after the decimal point; that is, the decimal point can float. There are also representations in which the number of digits before and after the decimal point is set, called fixed-point representations. In general, floating-point representations are slower and less accurate than fixed-point representations, but they can handle a larger range of numbers.

Note that most floating-point numbers a computer can represent are just approximations. One of the challenges in programming with floating-point values is ensuring that the approximations lead to reasonable results. If the programmer is not careful, small discrepancies in the approximations can snowball to the point where the final results become meaningless.

Because mathematics with floating-point numbers requires a great deal of computing power, many microprocessors come with a chip, called a floating point unit (FPU), specialized for performing floating-point arithmetic. FPUs are also called math coprocessors and numeric coprocessors.


floating-point unit

See FPU.


floppy disk

A soft magnetic disk. It is called floppy because it flops if you wave it (at least, the 5¼-inch variety does). Unlike most hard disks, floppy disks (often called floppies or diskettes) are portable, because you can remove them from a disk drive. Disk drives for floppy disks are called floppy drives. Floppy disks are slower to access than hard disks and have less storage capacity, but they are much less expensive. And most importantly, they are portable.

Floppies come in two basic sizes:

5¼-inch: The common size for PCs made before 1987. This type of floppy is generally capable of storing between 100K and 1.2MB (megabytes) of data. The most common sizes are 360K and 1.2MB.

3½-inch: Floppy is something of a misnomer for these disks, as they are encased in a rigid envelope. Despite their small size, microfloppies have a larger storage capacity than their cousins—from 400K to 1.4MB of data. The most common sizes for PCs are 720K (double-density) and 1.44MB (high-density). Macintoshes support disks of 400K, 800K, and 1.2MB.


floppy drive

Short for floppy disk drive, a disk drive that can read and write to floppy disks.


floptical

A type of disk drive technology that uses a combination of magnetic and optical techniques to achieve greater storage capacity than normal floppy disks without sacrificing access speeds.


flow

In desktop publishing, to insert a body of text into a document such that it wraps (or flows) around any objects on the page.


flush

(adj) Aligned along a margin. For example, text that is flush left is aligned along the left margin. Flush-right text is aligned along the right margin. For example:

This text is flush left.	This text is flush  right.
The opposite of flush is ragged. For example, the first example has a ragged right margin and the second example has a ragged left margin. Text that is both flush left and flush right is said to be justified.

(v) To copy data from a temporary storage area such as RAM to a more permanent storage medium such as a disk.


folder

In graphical user interfaces such as Windows and the Macintosh environment, a folder is an object that can contain multiple documents. Folders are used to organize information. In the DOS and UNIX worlds, folders are called directories.


font

A design for a set of characters. A font is the combination of typeface and other qualities, such as size, pitch, and spacing. For example, Times Roman is a typeface that defines the shape of each character. Within Times Roman, however, there are many fonts to choose from—different sizes, italic, bold, and so on. (The term font is often used incorrectly as a synonym for typeface.)

The height of characters in a font is measured in points, each point being approximately 1/72 inch. For example, the text in this book is printed with 9-point type. The width is measured by pitch, which refers to how many characters can fit in an inch. Common pitch values are 10 and 12. A font is said to be fixed pitch if every character has the same width. If the widths vary depending on the shape of the character, it is called a proportional font.

Most applications that support text enable you to choose from among many fonts. Laser, ink-jet, and dot-matrix printers offer the widest selection of fonts. These printers support a certain set of built-in fonts, but you can expand this set by loading different fonts from software (soft fonts) or from font cartridges.

Computers and devices use two methods to represent fonts. In a bit-mapped font, every character is represented by an arrangement of dots. To print a bit-mapped character, a printer simply locates the character's bit-mapped representation stored in memory and prints the corresponding dots. Each different font, even when the typeface is the same, requires a different set of bit maps.

The other method utilizes a vector graphics system to define fonts. In vector graphics systems, the shape or outline of each character is defined geometrically. The typeface can be displayed in any size, so a single font description really represents innumerable fonts. For this reason, vector fonts are called scalable fonts—they can be any size (scale). Other terms for vector fonts are object-oriented fonts or outline fonts. The most widely used scalable-font systems are PostScript and TrueType.

Aside from the scalability of vector fonts, their other main advantage over bit-mapped fonts is that they make the most of high-resolution devices. Bit-mapped fonts look almost the same whether printed on a 300-dpi printer or a 1,200-dpi printer. Vector fonts look better, the higher the resolution.

Despite the advantages of vector fonts, bit-mapped fonts are still widely used. One reason for this is that small vector fonts do not look very good on low-resolution devices, such as display monitors (which are low-resolution when compared with laser printers). Many computer systems, therefore, use bit-mapped fonts for screen displays. These are sometimes called screen fonts. In addition, some professionals prefer to use bit-mapped fonts on high-resolution printers because characters can be individually tailored to the printing device.

An additional drawback of vector fonts is that every character must be generated as it is needed. This is a computation-intensive process that requires a powerful microprocessor to make it acceptably fast.


font card

Same as font cartridge.


font cartridge

A ROM cartridge that contains one or more fonts. By inserting the cartridge into a laser printer, you give the printer the ability to print different fonts. Another way to load fonts into a printer is to download them from the computer's storage device.


font family

A set of fonts all with the same typeface, but with different sizes, weights and slants.


footer

One or more lines of text that appear at the bottom of every page of a document. Once you specify what text should appear in the footer, the application automatically inserts it.

Most applications allow you to use special symbols in the footer that represent changing values. For example, you can enter a symbol for the page number, and the application will replace the symbol with the correct number on each page. If you enter the date symbol, the application will insert the current date, which will change if necessary each time you print the document.

You can usually specify at least two different footers, one for odd-numbered pages (odd footer) and one for even-numbered pages (even footer).

A footer is sometimes called a running foot.


footprint

The amount of floor or desk space required by a device. For example, a small-footprint computer is a computer whose dimensions (width and depth) are relatively small.


forced page break

A page break that you explicitly insert. The application cannot override a forced page break. Forced page breaks are sometimes called hard page breaks.


foreground

(1) In multiprocessing systems, the process that is currently accepting input from the keyboard or other input device is sometimes called the foreground process.

(2) On display screens, the foreground consists of the characters and pictures that appear on the screen. The background is the uniform canvas behind the characters and pictures.


form feed

(1) Printers that use continuous paper normally have a form feed button or command that advances the paper to the beginning of the next page.

(2) A special character that causes the printer to advance one page length or to the top of the next page. In systems that use the ASCII character set, a form feed has a decimal value of 12. Form feed is sometimes abbreviated FF.


format

(v) (1) To prepare a storage medium, usually a disk, for reading and writing. When you format a disk, the operating system erases all bookkeeping information on the disk, tests the disk to make sure all sectors are reliable, marks bad sectors (that is, those that are scratched), and creates internal address tables that it later uses to locate information. You must format a disk before you can use it.

Note that reformatting a disk does not erase the data on the disk, only the address tables. Do not panic, therefore, if you accidentally reformat a disk that has useful data. A computer specialist should be able to recover most, if not all, of the information on the disk. You can also buy programs that enable you to recover a disk yourself.

The previous discussion, however, applies only to high-level formats, the type of formats that most users execute. In addition, hard disks have a low-level format, which sets certain properties of the disk such as the interleave factor. The low-level format also determines what type of disk controller can access the disk (e.g., RLL or MFM).

Almost all hard disks that you purchase have already had a low-level format. It is not necessary, therefore, to perform a low-level format yourself unless you want to change the interleave factor or make the disk accessible by a different type of disk controller. Performing a low-level format erases all data on the disk.

(2) To specify the properties, particularly visible properties, of an object. For example, word processing applications allow you to format text, which involves specifying the font, alignment, margins, and other properties.

(n) A particular arrangement. Almost everything associated with computers has a format.


forms software

A type of program that enables you to design and fill in forms on a computer. Most forms packages contain a number of sample forms that you can modify for your own purposes.


formula

(1) An equation or expression.

(2) In spreadsheet applications, a formula is an expression that defines how one cell relates to other cells. For example, you might define cell C5 (column C, row 5) with the formula

+A4*D7

which means to multiply the value in cell A4 by the value in cell D7.


FORTRAN

Acronym for formula translator, FORTRAN is the oldest high-level programming language. Designed by Jim Backus for IBM in the late 1950s, it is still popular today, particularly for scientific applications that require extensive mathematical computations.

The two most common versions of FORTRAN are FORTRAN IV and FORTRAN 77. FORTRAN IV was approved as a USASI standard in 1966. FORTRAN 77 is a version of FORTRAN that was approved by ANSI in 1978 (they had expected to approve it in 1977, hence the name). FORTRAN 77 includes a number of features not available in older versions of FORTRAN. A new ISO and ANSI standard for FORTRAN, called FORTRAN-90, was recently developed.


forum

An online discussion group. Online services and bulletin board services (BBS’s) provide a variety of forums, in which participants with common interests can exchange open messages. Forums are sometimes called newsgroups (in the Internet world) or conferences.


fourth-generation language

Often abbreviated 4GL, fourth-generation languages are programming languages closer to human languages than typical high-level programming languages. Most 4GLs are used to access databases. For example, a typical 4GL command is

FIND ALL RECORDS WHERE NAME IS “SMITH”

The other three generations of computer languages are

first generation: machine language

second generation: assembly language

third generation: high-level programming languages


fps

Stands for frames per second, a measure of how much information is used to store and display motion video. The term applies equally to film video and digital video. Each frame is a still image; displaying frames in quick succession creates the illusion of motion. The more frames per second (fps), the smoother the motion appears. Television in the U.S., for example, is based on the NTSC format, which displays 60 frames per second. In general, the minimum fps need to avoid jerky motion is about 30. Some computer video formats, such as AVI, provide only 15 frames per second.


FPU

Short for floating-point unit, a specially designed chip that performs floating-point calculations. Computers equipped with an FPU perform certain types of applications much faster than computers that lack one. In particular, graphics applications are faster with an FPU.

Some microprocessors, such as the Intel 80486 and Pentium, have a built-in FPU. With other microprocessors, you can usually add an FPU by inserting the FPU chip on the motherboard.

Floating-point units are also called numeric coprocessors, math coprocessors, and floating-point processors.


fractal

A word coined by Benoit Mandelbrot in 1975 to describe shapes that are “self-similar”—that is, shapes that look the same at different magnifications. To create a fractal, you start with a simple shape and duplicate it successively according to a set of fixed rules. Oddly enough, such a simple formula for creating shapes can produce very complex structures, some of which have a striking resemblance to objects that appear in the real world. For example, graphics designers use fractals to generate images of mountainous landscapes, coastlines, and flowers. In fact, many of the computer-generated images that appear in science fiction films utilize fractals.


fragmentation

(1) Refers to the condition of a disk in which files are divided into pieces scattered around the disk. Fragmentation occurs naturally when you use a disk frequently, creating, deleting, and modifying files. At some point, a file becomes too large for the space originally allotted for it, so the operating system splits the file into two or more chunks. This is entirely invisible to users, but it can slow down the speed at which data is accessed because the disk drive must search through different parts of the disk to put together a single file.

In DOS 6.0 and later systems, you can defragment a disk with the DEFRAG command. You can also buy software utilities, called disk optimizers or defragmenters, that defragment a disk .

(2) Fragmentation can also refer to RAM that has small, unused holes scattered throughout it.


frame

(1) In graphics and desktop publishing applications, a rectangular area in which text or graphics can appear.

(2) In communications, a packet of transmitted information.

(3) In video and animation, a single image. See under fps.


frames per second

See fps.


freeware

Copyrighted software given away for free by the author. Although it is available for free, the author retains the copyright, which means that you cannot do anything with it that is not expressly allowed by the author. Usually, the author allows people to use the software, but not sell it.


friction feed

A method of feeding paper through a printer. Friction-feed printers use plastic or rubber rollers to squeeze a sheet of paper and pull it through the printer.

The other principal form of feeding paper into a dot-matrix or daisy-wheel printer is through a tractor feed, in which sprocketed wheels on either side of the printer fit into holes in the paper. As the wheels revolve, the paper is pulled through the printer.

Tractor-feed printers require special paper, whereas friction-feed printers can handle most types of cut-sheet paper, including envelopes. Many printers support both types of feeding mechanisms.


front end

(1) For software applications, front end is the same as user interface.

(2) In client/server applications, the client part of the program is often called the front end and the server part is called the back end.

(3) Compilers, the programs that translate source code into object code, are often composed of two parts: a front end and a back end. The front end is responsible for checking syntax and detecting errors, whereas the back end performs the actual translation into object code.


frozen

Unresponsive. The term is used to describe a monitor, keyboard, or the entire computer when it no longer reacts to input due to a malfunction.


FTM

See flat technology monitor.


FTP

Abbreviation of File Transfer Protocol, the protocol used on the Internet for sending files.


full duplex

Refers to the transmission of data in two directions simultaneously. For example, a telephone is a full-duplex device because both parties can talk at once. In contrast, a walkie-talkie is a half-duplex device because only one party can transmit at a time.

Most modems have a switch that lets you choose between full-duplex and half-duplex modes. The choice depends on which communications program you are running.

In full-duplex mode, data you transmit does not appear on your screen until it has been received and sent back by the other party. This enables you to validate that the data has been accurately transmitted. If your display screen shows two of each character, it probably means that your modem is set to half-duplex mode when it should be in full-duplex mode.


full-length

See under expansion board and expansion slot.


function

(1) In programming, a named section of a program that performs a specific task. In this sense, a function is a type of procedure or routine. Some programming languages make a distinction between a function, which returns a value, and a procedure, which performs some operation but does not return a value.

Most programming languages come with a prewritten set of functions that are kept in a library. You can also write your own functions to perform specialized tasks.

(2) The term function is also used synonymously with operation and command. For example, you execute the delete function to erase a word.


function keys

Special keys on the keyboard that have different meanings depending on which program is running. Function keys are normally labeled F1 to F10 or F12 (or F15 on Macintoshes). On older PCs, for example, ten function keys are grouped on the left side of the keyboard; new PCs have the enhanced keyboard, with twelve function keys aligned along the top of the keyboard.


fuzzy logic

A type of logic that recognizes more than simple true and false values. With fuzzy logic, propositions can be represented with probabilities of truthfulness and falsehood. Fuzzy logic has proved to be particularly useful in expert system and other artificial applications. It is also used in some spell checkers to suggest a list of probable words to replace a misspelled one.


G

The symbol used for giga or gigabyte.


garbage in, garbage out

Often abbreviated as GIGO, this is a famous computer axiom meaning that if invalid data is entered into a system, the resulting output will also be invalid. Although originally applied to computer software, the axiom holds true for all systems, including, for example, decision-making systems.


gas-plasma display

A type of thin display screen, called a flat-panel display, used in some portable computers. A gas-plasma display works by sandwiching neon gas between two plates. One plate is coated with vertical wires and the other with horizontal wires, forming a grid. When electric current is passed through a horizontal and vertical wire, the gas at the intersection glows, creating a point of light, or pixel. You can think of a gas-plasma display as a collection of very small neon bulbs. Images on gas-plasma displays generally appear as orange objects on top of a black background.

Although gas-plasma displays produce very sharp monochrome images, they require much more power than the more common LCD displays.


gateway

In networking, a combination of hardware and software that links two different types of networks. Gateways between e-mail systems, for example, allow users on different e-mail systems to exchange messages. Contrast with Bridge, which connects to networks of the same type.


GB

Short for gigabyte.


GDI printer

A printer that has built-in support for Windows Graphical Device Interface (GDI). GDI is used by most Windows applications to display images on a monitor, so when printing from a Windows application to a GDI printer, there is no need to convert the output to another format such as PostScript or PCL.


GEM

A graphical user interface developed by Digital Research that is built into personal computers made by Atari, and is also used as an interface for some DOS programs. Like the Macintosh interface and Microsoft Windows, GEM provides a windowed environment for running programs.

GEM also refers to a special graphics file format used in GEM-based applications.


genlock

Short for generator locking device, a genlock is a device that enables a composite video machine, such as a TV, to accept two signals simultaneously. A genlock locks one set of signals while it processes the second set. This enables you to combine graphics from a computer with video signals from a second source such as a video camera.


GIF

Pronounced jiff, stands for graphics interchange format, a bit-mapped graphics file format used by the World Wide Web,  CompuServe and many BBSs. GIF supports color and various resolutions. It also includes data compression, making it especially effective for scanned photos.


giga (G)

(1) When decimal notation is used, giga stands for one billion. For example, a gigavolt is 1 billion volts.

(2) When applied to computers, which use the binary  notation system, giga represents 2 to the 30th power, which is 1,073,741,824, a little more than 1 billion. A gigabyte, therefore, is about 1.073 billion bytes.


gigabyte

2 to the 30th power (1,073,741,824) bytes. One gigabyte is equal to 1,024 megabytes. Gigabyte is often abbreviated as G or GB.


GIGO

See garbage in, garbage out.


glitch

A malfunction. Glitch is sometimes used as a synonym for bug, but more often it refers to a hardware problem.


gopher

A menu-based program that helps Internet users find files and other resources. It was developed at the University of Minnesota and named after the school’s mascot. It is a particularly apt name, because the program excels at digging out otherwise difficult-to-find information.


gppm

Abbreviation for graphics pages per minute, the speed with which laser printers can print nontext pages. Typically, laser printers are rated in terms of pages per minute (ppm), but this refers only to the speed with which they print text pages. The gppm is always much less and may be the more important figure if you are using the printer to print graphics-intensive documents.


grabber

(1) A device that captures data. The term is used most often to describe devices that can capture full-motion video from a television or video camera and convert it to digital form for storage on a computer’s disk.

(2) In some applications, a special tool or cursor that enables you to grab objects on the screen and move them or manipulate them in some other way. A grabber cursor is often represented by a hand icon.


graphical user interface (GUI)

A program interface that takes advantage of the computer's graphics capabilities to make the program easier to use. Well-designed graphical user interfaces can free the user from learning complex command languages. On the other hand, many users find that they work more effectively with a command-driven interface, especially if they already know the command language.

Graphical user interfaces, such as Microsoft Windows and the one used by the Apple Macintosh, feature the following basic components:

pointer: A symbol that appears on the display screen and that you move to select objects and commands. Usually, the pointer appears as a small angled arrow. Text-processing applications, however, use an I-beam pointer that is shaped like a capital I.

pointing device: A device, such as a mouse or trackball, that enables you to select objects on the display screen.

icons: Small pictures that represent commands, files, or windows. By moving the pointer to the icon and pressing a mouse button, you can execute a command or convert the icon into a window. You can also move the icons around the display screen as if they were real objects on your desk.

desktop: The area on the display screen where icons are grouped is often referred to as the desktop because the icons are intended to represent real objects on a real desktop.

windows: You can divide the screen into different areas. In each window, you can run a different program or display a different file. You can move windows around the display screen, and change their shape and size at will.

menus: Most graphical user interfaces let you execute commands by selecting a choice from a menu.

The first graphical user interface was designed by Xerox Corporation's Palo Alto Research Center in the 1970s, but it was not until the 1980s and the emergence of the Apple Macintosh that graphical user interfaces became popular. One reason for their slow acceptance was the fact that they require considerable CPU power and a high-quality monitor, which until recently were prohibitively expensive.

In addition to their visual components, graphical user interfaces also make it easier to move data from one application to another. A true GUI includes standard formats for representing text and graphics. Because the formats are well-defined, different programs that run under a common GUI can share data. This makes it possible, for example, to copy a graph created by a spreadsheet program into a document created by a word processor.

Many DOS programs include some features of GUIs, such as menus, but are not graphics based. Such interfaces are sometimes called graphical character-based user interfaces to distinguish them from true GUIs.


graphics

Pertains to any computer device or program that makes a computer capable of displaying and manipulating pictures. For example, laser printers and plotters are graphics devices because they permit the computer to output pictures. A graphics monitor is a display monitor that can display pictures. A graphics board (or graphics card) is a printed circuit board that, when installed in a computer, permits the computer to display pictures.

Many software applications include graphics components. Such programs are said to support graphics. For example, certain word processors support graphics because they let you draw or import pictures. All CAD/CAM systems support graphics. Some database management systems and spreadsheet programs support graphics because they let you display data in the form of graphs and charts. Such applications are often referred to as business graphics.

The following are also considered graphics applications:

paint programs: Allow you to create rough freehand drawings. The images are stored as bit maps and can easily be edited.

illustration/design programs: Supports more advanced features than paint programs, particularly for drawing curved lines. The images are usually stored in vector-based formats. Illustration/design programs are often called draw programs.

presentation graphics software: Lets you create bar charts, pie charts, graphics, and other types of images for slide shows and reports. The charts can be based on data imported from spreadsheet applications.

animation software: Enables you to chain and sequence a series of images to simulate movement. Each image is like a frame in a movie.

CAD software: Enables architects and engineers to draft designs.

desktop publishing: Provides a full set of word-processing features as well as fine control over placement of text and graphics, so that you can create newsletters, advertisements, books, and other types of documents.

In general, applications that support graphics require a powerful CPU and a large amount of memory. Many graphics applications—for example, computer animation systems—require more computing power than is available on personal computers and will run only on powerful workstations or specially designed graphics computers. This is true of all three-dimensional computer graphics applications.

In addition to the CPU and memory, graphics software requires a graphics monitor and support for one of the many graphics standards. Most PC programs, for instance, require VGA graphics. If your computer does not have built-in support for a specific graphics system, you can insert a video adapter card.

The quality of most graphics devices is determined by their resolution—how many points per square inch they can represent—and their color capabilities.


graphics accelerator

A special type of video adapter that contains its own processor to boost performance levels. These processors are specialized for computing graphical transformations, so they achieve better results than the general-purpose CPU used by the computer. In addition, they free up the computer’s CPU to execute other commands while the graphics accelerator is handling graphics computations.

The popularity of graphical applications, and especially multimedia applications, has made graphics accelerators not only a common enhancement, but a necessity. Most computer manufacturers now bundle a graphics accelerator with their mid-range and high-end systems.

Aside from the graphics processor used, the other characteristics that differentiate graphics accelerators are:

memory: Graphics accelerators have their own memory, which is reserved for storing graphical representations. The amount of memory determines how much resolution and how many colors can be displayed. Some accelerators use conventional DRAM, but others use a special type of video RAM (VRAM), which enables both the video circuitry and the processor to simultaneously access the memory.

bus: Each graphics accelerator is designed for a particular type of video bus. As of 1995, most are designed for the PCI bus.

register width: The wider the register, the more data the processor can manipulate with each instruction. 64-bit accelerators are already becoming common, and we can expect 128-bit accelerators in the near future.


graphics adapter

Same as video adapter.


graphics based

Refers to software and hardware that treat objects on a display screen as bit maps or geometrical shapes rather than as characters. In contrast, character-based systems treat everything as ASCII or extended ASCII characters.

All graphics software is by definition graphics based. Systems that manipulate text can also be graphics based; for example, desktop publishing systems are essentially graphics-based word processors.

Traditionally, most DOS applications—word processors, spreadsheets, and database management systems—have been character based. This enables them to run on any PC, even those with limited CPU, memory, and graphics capabilities. Increasingly, however, software manufacturers are spurning backward compatibility to create fully graphics-based applications.

Because the Macintosh is a graphical computer, all programs that run on a Macintosh computer are graphics based.


graphics character

A character that represents a shape. By combining graphics characters, even character-mode programs can display rudimentary graphics, known as block graphics. Many of the characters in the extended ASCII character set are graphics characters.


graphics coprocessor

A microprocessor specially designed for handling graphics computations. Most graphics accelerators include a graphics coprocessor.


graphics display system

The combination of monitor and video adapter that makes a computer capable of displaying graphics.


graphics file formats

A file format designed specifically for representing graphical images. Graphics file formats can be broadly categorized into bit-mapped formats and vector formats.Table: Bit-Mapped formats and Table:Vector formats list the most common of both file formats.


graphics mode

Many video adapters support several different modes of resolution, all of which are divided into two general categories: character mode and graphics mode. In character mode, the display screen is treated as an array of blocks, each of which can hold one ASCII character. In graphics mode, the display screen is treated as an array of pixels. Characters and other shapes are formed by turning on combinations of pixels.

Of the two modes, graphics mode is the more sophisticated. Programs that run in graphics mode can display an unlimited variety of shapes and fonts, whereas programs running in character mode are severely limited. Programs that run entirely in graphics mode are called graphics-based programs.


graphics monitor

A monitor capable of displaying graphics. That is, any monitor that supports a graphics mode in addition to text modes. Nearly all modern monitors are graphics monitors.


graphics pages per minute

See gppm.


graphics tablet

Same as digitizing tablet.


gray scaling

The use of many shades of gray to represent an image. Continuous-tone images, such as black-and-white photographs, use an almost unlimited number of shades of gray. Conventional computer hardware and software, however, can only represent a limited number of shades of gray (typically 16 or 256). Gray-scaling is the process of converting a continuous-tone image to an image that a computer can manipulate.

While gray scaling is an improvement over monochrome, it requires larger amounts of memory because each dot is represented by from 4 to 8 bits. At a resolution of 300 dpi, you would need about 6 megabytes to represent a single 8½ by 11-inch page using 256 shades of gray. This can be reduced somewhat through data compression techniques, but gray scaling still requires a great deal of memory.

Many optical scanners are capable of gray scaling, using from 16 to 256 different shades of gray. However, gray scaling is only useful if you have an output device—monitor or printer—that is capable of displaying all the shades. Most color monitors are capable of gray scaling, but the images are generally not as good as on dedicated gray-scaling monitors.

Note that gray scaling is different from dithering. Dithering simulates shades of gray by altering the density and pattern of black and white dots. In gray scaling, each individual dot can have a different shade of gray.


greeking

(1) The approximation of text characters on a screen display. Greeking is often used by word processors that support a preview function. In preview mode, the word processor attempts to show what a document will look like when printed. Frequently, however, the graphics display capabilities of the monitor are not sufficient to show text at a small size. To give a general idea of what the text will look like and how page layout will appear, the word processor uses graphics symbols to approximate the text. These symbols suggest greek letters, hence the term greeking.

(2) The term greeking is also used to describe nonsense text inserted in a document to check a layout. This allows a layout artist to concentrate on the overall appearance of a page without worrying about the actual text that will be inserted later.


green PC

A PC especially designed to minimize power consumption. Green PCs draw less power than normal PCs and support sleep modes, in which the computer powers down all unnecessary components when it is inactive.


Group 3 protocol

The universal protocol defined by the CCITT for sending faxes.


Group 4 protocol

A protocol defined by CCITT for sending faxes over ISDN networks.


groupware

A class of software that helps groups of colleagues (workgroups) attached to a local-area network organize their activities. Typically, groupware supports the following operations:

•	scheduling meetings and allocating resources

•	e-mail

•	password protection for documents

•	telephone utilities

•	electronic newsletters

Groupware is sometimes called workgroup productivity software.


GUI

Pronounced goo-ee, acronym for graphical user interface. See under graphical user interface.


gutter

In desktop publishing, the space between columns in a multiple-column document.


GW-BASIC

A dialect of the BASIC programming language that comes with many versions of the DOS operating system.


hack

(n) An inelegant and usually temporary solution to a problem.

(v) To modify a program, often in an unauthorized manner, by changing the code itself.


hacker

A slang term for a computer enthusiast. Among professional programmers, the term hacker implies an amateur or a programmer who lacks formal training. Depending on how it used, the term can be either complimentary or derogatory, although it is developing an increasingly derogatory connotation. The pejorative sense of hacker is becoming more prominent largely because the popular press has coopted the term to refer to individuals who gain unauthorized access to computer systems for the purpose of stealing and corrupting data.


half duplex

Refers to the transmission of data in just one direction at a time. For example, a walkie-talkie is a half-duplex device because only one party can talk at a time. In contrast, a telephone is a full-duplex device because both parties can talk simultaneously.

Most modems contain a switch that lets you select between half-duplex and full-duplex modes. The correct choice depends on which program you are using to transmit data through the modem.

In half-duplex mode, each character transmitted is immediately displayed on your screen. (For this reason, it is sometimes called local echo—characters are echoed by the local device). In full-duplex mode, transmitted data is not displayed on your monitor until it has been received and returned (remotely echoed) by the other device. If you are running a communications program and every character appears twice, it probably means that your modem is in half-duplex mode when it should be in full-duplex mode, and every character is being both locally and remotely echoed.


half height

PCs support both full-height and half-height bays for disk drives and other mass storage devices. The half-height models take up less space but usually have less storage capacity.


halftone

In printing, a continuous tone image, such as a photograph, that has been converted into a black-and-white image. Halftones are created through a process called dithering, in which the density and pattern of black and white dots are varied to simulate different shades of gray.

In conventional printing, halftones are created by photographing an image through a screen. The screen frequency, measured in lines per inch, determines how many dots are used to make each spot of gray. In theory, the higher the screen frequency (the more lines per inch), the more accurate the halftone will be. However, actual screen frequencies are limited by the technology because higher screen frequencies create smaller, more tightly packed dots. If you are printing on a low resolution device, therefore, you may get better results with a lower screen frequency.

Modern desktop publishing systems can create halftones by simulating the conventional photographic process. This is why some programs allow you to specify a screen frequency even when no actual screen is used.


hand-held computer

A portable computer that is small enough to be held in one’s hand. Although extremely convenient to carry, handheld computers have not replaced notebook computers because of their small keyboards and screens. The most popular hand-held computers are those that are specifically designed to provide PIM (personal information manager) functions, such as a calendar and address book.

Some manufacturers are trying to solve the small keyboard problem by replacing the keyboard with an electronic pen. However, these pen-based devices rely on handwriting recognition technologies, which are still in their infancy.


handle

(1) In many applications, when you select a graphical object, an outline of the object appears with small boxes. Each box is a handle. By dragging the handles, you can change the shape and size of the object.

(2) In programming, a handle is a token, typically a pointer, that enables the program to access a resource, such as a library function.

(3) When communicating via an online service, your handle is the name that you use to identify yourself. It could be your real name, a nickname, or a completely fictitious name.


handshaking

The process by which two devices initiate communications. Handshaking begins when one device sends a message to another device indicating that it wants to establish a communications channel. The two devices then send several messages back and forth that enable them to agree on a communications protocol.


handwriting recognition

The technique by which a computer system can recognize characters and other symbols written by hand. In theory, handwriting recognition should free us from our keyboards, allowing us to write and draw in a more natural way. It is considered one of the key technologies that will determine the ultimate success or failure of PDAs and other hand-held devices. To date, however, the technology has had only limited success. This is partly because it is still a young technology and is not as fast or accurate as it needs to be. Another reason for its slow acceptance, however, is that the keyboard is in fact more convenient in many situations. Many people can write much faster with a keyboard than they can by hand.


hang

To crash in such a way that the computer does not respond to input from the keyboard or mouse. If your computer is hung, you usually need to reboot it, although sometimes hitting the correct sequence of control characters will free it up.


hanging indent

In word processing, a paragraph that has all lines but the first indented. For example:

This is an example of a hanging indent. A hanging indent is also known as a hanging paragraph.

With many word processors, you can create hanging indents by specifying a negative indentation for the first line of each paragraph.


hanging paragraph

Same as hanging indent.


hard

The term hard is used to describe anything that is permanent or physically exists. In contrast, the term soft refers to concepts, symbols and other intangible and changeable objects.


hard card

A hard disk drive and controller on an expansion card. Unlike most disk drives that are either external to the computer or fit in one of the disk drive bays, a hard card slips into an expansion slot. Hard cards are often faster than conventional disk drives, and easier to install. Their storage capacities, however, are more limited.


hard coded

Unchangeable. Hard-coded features are built into the hardware or software in such a way that they cannot be modified.


hard copy

A printout of data stored in a computer. It is considered hard because it exists physically on paper, whereas a soft copy exists only electronically.


hard disk

A magnetic disk on which you can store computer data. The term hard is used to distinguish it from a soft, or floppy, disk. Hard disks hold more data and are faster than floppy disks. A hard disk, for example, can store anywhere from 10 megabytes to over one gigabyte, whereas most floppies have a maximum storage capacity of 1.4 megabytes.

A single hard disk usually consists of several platters. Each platter requires two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they cannot move independently. Each platter has the same number of tracks, and a track location that cuts across all platters is called a cylinder. For example, a typical 84 megabyte hard disk for a PC might have two platters (four sides) and 1,053 cylinders.

In general, hard disks are less portable than floppies, although it is possible to buy removable hard disks. There are two types of removable hard disks: disk packs and removable cartridges.


hard disk drive

The mechanism that reads and writes data on a hard disk. Hard disk drives for PCs generally have access times of about 15 milliseconds or less. Many disk drives improve their performance through a technique called caching.

The disk drives for hard disks are called hard disk drives or Winchester drives, Winchester being the name of one of the first popular hard disk drive technologies developed by IBM in 1973.

There are several interface standards for passing data between a hard disk and a computer. The most common are:

ST-506: The standard interface on all PC/XT and PC/AT computers. The ST-506 standard supports both MFM and RLL encoding formats.

SCSI (Small Computer System Interface): The standard interface for Apple Macintoshes, SCSI is also popular on UNIX systems and is available on many PC compatibles.

IDE (Integrated Drive Interface): Not as fast as SCSI, but faster than ST-506.

Enhanced IDE: A new version of the IDE interface that supports data transfer rates comparable to SCSI.


hard disk type

A number that indicates important features of a hard disk, such as the number of platters and cylinders. Hard disk manufacturers have agreed on a numbering scheme so that it is possible to install and configure a new hard disk simply by entering the disk’s type number into the BIOS setup.


hard drive

Same as hard disk drive.


hard hyphen

See under hyphenation.


hard return

A return is the process of jumping from the end of one line of text to the beginning of the next line. Word processors utilize two types of returns: hard returns and soft returns.

A hard return is an actual symbol inserted into the text. The hard-return symbol is usually invisible, but most word processors support a mode that lets you see them. Whenever you press the Return or Enter key while editing a document, the word processor inserts a hard return.

Hard returns cause the word processor to start a new line regardless of how margins are set. Therefore, if a document contains hard returns, the lines will end at the same place even if you change the margins. In contrast, soft returns, inserted by the program rather than the user, depend on how the margins are set.


hardware

Refers to objects that you can actually touch, like disks, disk drives, display screens, keyboards, printers, boards, and chips. In contrast, software is untouchable. Software exists as ideas, concepts, and symbols, but it has no substance.

Books provide a useful analogy for describing the difference between software and hardware. The pages and the ink are the hardware, while the words, sentences, paragraphs, and the overall meaning are the software. A computer without software is like a book full of blank pages—you need software to make the computer useful just as you need words to make a book meaningful.


hardwired

Refers to elements of a program or device that cannot be changed. Originally, the term was used to describe functionality that was built into the circuitry (i.e., the wires) of a device. Nowadays, however, the term is also used to describe constants built into software.


Hayes compatible

Hayes Microcomputer Products is one of the leading manufacturers of modems and has developed a language for controlling modems that has become the de facto standard. Any modem that recognizes Hayes modem commands is said to be Hayes-compatible. This is very useful because many communications programs use Hayes modem commands.


head

The mechanism that reads data from or writes data to a magnetic disk or tape. If the head becomes dirty, it will not work properly. This is one of the first things to check if your disk drive or tape drive begins to malfunction.

The head is sometimes called a read/write head. Double-sided floppy disk drives have two heads, one for each side of the disk. Hard disk drives have many heads, two for each platter.


head crash

A serious disk drive malfunction. A head crash usually means that the head has scratched or burned the disk. In a hard disk drive, the head normally hovers a few microinches from the disk. If the head becomes misaligned or if dust particles come between it and the disk, it can touch the disk. When this happens, you usually lose much of the data on the hard disk and will need to replace both the head and the disk. For this reason, it is important to operate disk drives, particularly hard disk drives, in as clean an environment as possible. Even smoke particles can cause a head crash.

Head crashes are less common for floppy disks because the head touches the disk anyway under normal operation.

Another term for head crash is disk crash.


header

(1) In word processing, a line of text that appears at the top of each page of a document. Once you specify the text that should appear in the header, the word processor automatically inserts it.

Most word processors allow you to use special symbols in the header that represent changing values. For example, you can enter a symbol for the page number, and the word processor will automatically replace the symbol with the correct number on each page. If you enter the date symbol, the word processor will insert the current date, which will change if necessary each time you print the document.

Most word processors allow you to specify different headers, for example, one for odd-numbered pages (odd headers) and another for even-numbered pages (even headers). Headers are also called running heads.

(2) In many disciplines of computer science, a header is a unit of information that precedes a data object. In file management, for example, a header is a region at the beginning of each file where bookkeeping information is kept. The file header may contain the date the file was created, the date it was last updated, and the file's size. The header can be accessed only by the operating system or by specialized programs.


helical-scan cartridge

A type of magnetic tape that uses the same technology as VCR tapes. The term helical scan usually refers to 8 mm tapes, although 4 mm tapes (called DAT tapes) use the same technology. The 8 mm helical-scan tapes have data capacities from 2.5GB to 5GB.


Help

Online documentation. Many programs come with the instruction manual, or a portion of the manual, integrated into the program. If you encounter a problem or forget a command while running the program, you can summon the documentation by pressing a designated Help key or entering a HELP command. In Windows, the Help key is the function key labeled F1.

Once you summon the Help system, the program often displays a menu of Help topics. You can choose the appropriate topic for whatever problem you are currently encountering. The program will then display a help screen that contains the desired documentation.

Some programs are more sophisticated, displaying different Help messages depending on where you are in the program. Such systems are said to be context sensitive.

The Macintosh Help system is often referred to as Balloon Help because the help messages appear in a cartoon-like balloon. Newer Macs (starting with System 7.5) also have something called Interactive Help, which contains tutorials that show you how to perform different operations.


Hercules graphics

A graphics display system for PCs developed by Van Suwannukul, founder of Hercules Computer Technology. Suwannukul developed the system so that he could produce his doctoral thesis on PC equipment using his native Thai alphabet.

First offered in 1982, the original Hercules system filled a void left by IBM's MDA (monochrome display adapter) system. MDA produces high-resolution monochrome text but cannot generate graphics. Hercules systems generate both high-resolution text and graphics for monochrome monitors. The resolution is 720 by 348.


heterogeneous network

A network that includes computers and other devices from different manufacturers. For example, local-area networks (LANs) that connect PCs with Apple Macintosh computers are heterogeneous.


Hewlett-Packard Graphics Language

See HPGL.


hex

Short for hexadecimal.


hexadecimal

Refers to the base-16 number system, which consists of 16 unique symbols: the numbers 0 to 9 and the letters A to F. For example, the decimal number 15 is represented as F in the hexadecimal numbering system. The hexadecimal system is useful because it can represent every byte (8 bits) as two consecutive hexadecimal digits. It is easier for humans to read hexadecimal numbers than binary  numbers.

To convert a value from hexadecimal to binary , you merely translate each hexadecimal digit into its 4-bit binary  equivalent. For example, the hexadecimal number

3F7A

translates to the following binary  number:

0011 1111 1000 1010


hidden file

A file with a special hidden attribute turned on, so that the file is not normally visible to users. For example, hidden files are not listed when you execute the DOS DIR command. However, most file management utilities allow you to view hidden files.

DOS hides some files, such as MSDOS.SYS and IO.SYS, so that you will not accidentally corrupt them. You can also turn on the hidden attribute for any normal file, thereby making it invisible to casual snoopers. On a Macintosh, you can hide files with the ResEdit utility.


hierarchical

Refers to systems that are organized in the shape of a pyramid, with each row of objects linked to objects directly beneath it. Hierarchical systems pervade everyday life. The army, for example, which has generals at the top of the pyramid and privates at the bottom, is a hierarchical system. Similarly, the system for classifying plants and animals according to species, family, genus, and so on, is also hierarchical.

Hierarchical systems are as popular in computer systems as they are in other walks of life. The most obvious example of a hierarchical system in computers is a file system, in which directories have files and subdirectories beneath them. Such a file organization is, in fact, called a hierarchical file system.

In addition to file systems, many data structures for storing information are hierarchical in form. Menu-driven programs are also hierarchical, because they contain a root menu at the top of the pyramid and submenus below it.


high ASCII

Same as extended ASCII.


high memory

In DOS-based systems, high memory refers to the memory area between the first 640K and 1 megabyte. It is also called the upper memory area.


high memory area

In DOS-based systems, the high memory area refers to the first 64K of extended memory.


high resolution

See under resolution.


high-density disk

A high-quality floppy disk capable of holding more data than a double-density disk. High-density 5¼-inch disks for PCs can hold 1.2MB (megabytes) of data. High-density 3½-inch disks can store 1.44MB.


high-level language

A programming language such as C, FORTRAN, or Pascal that enables a programmer to write programs that are more or less independent of a particular type of computer. Such languages are considered high-level because they are closer to human languages and further from machine languages. In contrast, assembly languages are considered low-level because they are very close to machine languages.

The main advantage of high-level languages over low-level languages is that they are easier to read, write, and maintain. Ultimately, programs written in a high-level language must be translated into machine language by a compiler or interpreter.

The first high-level programming languages were designed in the 1950s. Now there are dozens of different languages, including Ada, Algol, BASIC, COBOL, C, C++, FORTRAN, LISP, Pascal, and PROLOG.


highlight

To make an object on a display screen stand out by displaying it in a different mode from other objects. Typical highlighted objects include menu options, command buttons, and selected blocks of text.


home computer

A personal computer specially configured for use in a home rather than an office. Typically, home computers have only medium-power microprocessors, but are equipped with a full complement of multimedia devices. In addition, manufacturers often bundle recreational and educational software with home computers.


Home key

A key on PC and newer Macintosh keyboards that controls cursor movement. Usually, the Home key moves the cursor to the top left corner of the screen or to the beginning of the file, but it can have other meanings depending on which program is running.


home page

The main page of a web site. Typically, the home page serves as an index or table of contents to other documents stored at the site.


host

A computer system that is accessed by a user working at a remote location. Typically, the term is used when there are two computer systems connected by modems and telephone lines. The system that contains the data is called the host, while the computer at which the user sits is called the remote terminal.


hot key

A user-defined key sequence that executes a command or causes the operating system to switch to another program. In DOS systems, for example, you can use hot keys to open memory-resident programs (TSRs). In Windows environments, you can often press a hot key to execute common commands. For example, Ctrl+C usually copies the selected objects.


hot link

(n) A link between two applications such that changes in one affect the other. For example, some desktop publishing systems let you establish hot links between documents and databases or spreadsheets. When data in the spreadsheet changes, the corresponding charts and graphs in the document change accordingly.

(v) To establish a link between two applications.


hot spot

An area of a graphics object, or a section of text, that activates a function when selected. Hot spots are particularly common in multimedia applications, where selecting a hot spot can make the application display a picture, run a video, or open a new window of information.


HP-compatible printer

Hewlett-Packard was one of the first companies to produce a laser printer for PCs, and most software products include drivers for HP printers. The drivers control the printers through a language called PCL (printer control language). Other manufacturers of laser printers design their printers so that they, too, understand PCL, making them able to emulate HP printers. In this way, their printers are HP-compatible and are thus automatically supported by many software products.

No non-HP printer, however, is 100 percent HP-compatible. Manufacturers claim HP compatibility even if their printers only recognize a subset of PCL commands. Note also that there are different versions of PCL. A printer may be able to emulate an HP LaserJet Plus but not a LaserJet II. Finally, HP laser printers support font cartridges, and not all HP-compatible printers can accept the same cartridges.


HPGL

Abbreviation of Hewlett-Packard Graphics Language, a set of commands for controlling plotters and printers. HPGL is part of Hewlett-Packard’s PCL Level 5 page description language.


HTML

Short for Hypertext Markup Language, the authoring language used to create documents on the World Wide Web. HTML is similar to SGML, although it is not a strict subset.


human engineering

Same as ergonomics.


HyperCard

A hypertext programming environment for the Macintosh introduced by Apple in 1987. The HyperCard model consists of cards, and collections of cards, called stacks. You can connect the cards in various ways, and leaf through them the way you would with a set of Rolodex cards. In addition to data, each card can contain graphics and buttons that trigger other events, such as sound or video.

Each object in a HyperCard system—stack, card, text field, button, or background—can have a script associated with it. A script is a set of instructions that specify what actions should take place when a user selects an object with the mouse or when some other event  occurs.

Writing HyperCard applications is known as authoring.


hypertext

A special type of database system, invented by Ted Nelson in the 1960s, in which objects (text, pictures, music, programs, and so on) can be creatively linked to each other. When you select an object, you can see all the other objects that are linked to it. You can move from one object to another even though they might have very different forms. For example, while reading a document about Mozart, you might click on the phrase Violin Concerto in A Major, which could display the written score or perhaps even invoke a recording of the concerto. Clicking on the name Mozart might cause various illustrations of Mozart to appear on the screen. The icons that you select to view associated objects are called Hypertext links or buttons.

Hypertext systems are particularly useful for organizing and browsing through large databases that consist of disparate types of information. There are several Hypertext systems available for Apple Macintosh computers and PCs that enable you to develop your own databases. Such systems are often called authoring systems. HyperCard software from Apple Computer is the most famous.


Hypertext Markup Language

See HTML.


hyphenation

In word processing, hyphenation refers to splitting a word that would otherwise extend beyond the right margin. Not all word processors support hyphenation, and of those that do support it, not all perform it correctly.

Word processors use two basic techniques to perform hyphenation. The first employs an internal dictionary of words that indicates where hyphens may be inserted. The second uses a set of logical formulas to make hyphenation decisions. The dictionary method is more accurate but is usually slower. The most sophisticated programs use a combination of both methods.

Most word processors allow you to override their own hyphenation rules and define yourself where a word should be divided.

Hyphens inserted automatically by a hyphenation utility are called discretionary or soft hyphens. Hyphens that you add explicitly by entering the dash character are called hard hyphens.


I-beam pointer

A pointer shaped like a capital I used in graphics-based text processing applications. Many desktop publishing systems and word processors use an I-beam pointer to mark blocks of text and move the insertion point. Note that the I-beam pointer is not the same as the selection pointer, which is usually shaped like an arrow.


I/O

Short for input/output, and pronounced eye-oh. I/O refers to any operation, program, or device whose purpose is to enter data into a computer or to extract data from a computer.

One usually uses the term I/O to distinguish noncomputational parts of a program from other parts that are strictly computational, or to distinguish certain devices from other devices. For example, a printer is an I/O device, whereas a CPU is a computational device.

All computer applications contain both I/O and computational parts. A word-processing system, for instance, contains I/O components (for entering, displaying, and printing text) as well as non-I/O components (for checking spelling, searching for words, and so on).


IBM compatible

See under IBM PC.


IBM PC

Refers to a family of personal computers produced by IBM. The term can also refer to computers that conform to set of loosely controlled standards. These are also called IBM clones, IBM compatibles, or simply compatibles. These terms are actually misnomers because many of the PCs produced by IBM do not conform to industry standards. For example, IBM attempted to change the expansion bus to MCA in its PS/2 line of PCs, but the industry did not follow suit.


icon

A small picture that represents an object or program. Icons are very useful in applications that use windows, because with the click of a mouse button you can shrink an entire window into a small icon. (This is sometimes called minimizing.) To redisplay the window, you merely move the pointer to the icon and click (or double click) a mouse button. (This is sometimes called restoring or maximizing)

Icons are a principal feature of graphical user interfaces.


IDE interface

Abbreviation of either Intelligent Drive Electronics or Integrated Drive Electronics, depending on who you ask. An IDE interface is an interface for mass storage devices, in which the controller is integrated into the disk or CD-ROM drive. It is a low-cost alternative to SCSI interfaces.

The original IDE interface supports data transfer rates of about 3.3 megabytes per second and has a limit of 538 megabytes per device. However, a recent version of IDE, called enhanced IDE (EIDE) or Fast IDE, supports data transfer rates of about 12 megabytes per second and 18.4 gigabytes per second. These numbers are comparable to what SCSI offers. To take advantage of EIDE, you need both an EIDE mass storage device and an EIDE interface installed in your computer.


identifier

Same as name. The term identifier is usually used for variable names.


IEEE

Abbreviation of Institute of Electrical and Electronic Engineers, pronounced I-triple-E. Founded in 1963, the IEEE is an organization composed of engineers, scientists, and students. The IEEE is best know for developing standards for the computer and electronics industry. In particular, the IEEE 802 standards for local-area networks are widely followed.


IGES

Acronym for Initial Graphics Exchange Specification, an ANSI graphics file format for three-dimensional wire frame models.


image editor

A graphics program that provides a variety of special features for altering bit-mapped images. The difference between image editors and paint programs is not always clear-cut, but in general image editors are specialized for modifying bit-mapped images, such as scanned photographs, whereas paint programs are specialized for creating images.

In addition to offering a host of filters and image transformation algorithms, image editors also enable you to create and superimpose layers.


image enhancement

In computer graphics, the process of improving the quality of a digitally stored image by manipulating the image with software. It is quite easy, for example, to make an image lighter or darker, or to increase or decrease contrast. Advanced image enhancement software also supports many filters for altering images in various ways. Programs specialized for image enhancement are sometimes called image editors.


imagesetter

A typesetting device that produces very high-resolution output on paper or film. Imagesetters are too expensive for homes or most offices, but you can obtain imagesetter output by bringing a PostScript file to a service bureau. One reason that PostScript has become the standard for desktop publishing is that nearly all imagesetters support it. This means that you can produce drafts on an inexpensive PostScript laser printer with high assurance that the final output from an imagesetter will look the same, but with higher resolution (up to 3,540 dots per inch).


ImageWriter

Refers to any in a family of dot-matrix printers that Apple offers for the Macintosh computer. Laser printers for the Macintosh are called LaserWriters.


IMAP

Short for Internet Message Access Protocol.


impact printer

Refers to a class of printers that work by banging a head or needle against an ink ribbon to make a mark on the paper. This includes dot-matrix printers, daisy-wheel printers, and line printers. In contrast, laser and ink-jet printers are nonimpact printers. The distinction is important because impact printers tend to be considerably noisier than nonimpact printers but are useful for multipart forms such as invoices.


import

To use data produced by another application. The ability to import data is very important in software applications because it means that one application can complement another. Many programs, for example, are designed to be able to import graphics in a variety of formats.

The opposite of importing is exporting, which refers to the ability of one application to format data for another application.


inclusive OR operator

A Boolean operator that returns a value of TRUE if either of its operands is TRUE. Contrast with the exclusive OR operator, which returns a value of TRUE only if both operands have different values.


increment

(v) To add a fixed amount. For example, if you count consecutively from 1 to 10, you increment by one. If you count by twos, you increment by two. A large proportion of computer software consists of loops of instructions in which one or more values are incremented each time the loop is executed.

(n) An amount that is added. For example, if you count by threes, the increment is three.


incremental backup

A backup procedure that backs up only those files that have been modified since the previous backup. Contrast with an archival backup, in which all files are backed up regardless of whether they have been modified since the last backup.


Indeo

A codec (compression/decompression technology) for computer video developed by Intel Corporation. Although it is a software-only codec, Indeo is based on the DVI, which is a hardware-only codec.

Competing video standards include Cinepak and MPEG.


Industry Standard Architecture (ISA) bus

The bus architecture used in the IBM PC/XT and PC/AT. The AT version of the bus is called the AT bus and has become a de facto industry standard. Since the late 80s, the industry has been searching for a successor to the ISA bus, which is not sufficient for modern devices and applications. It now appears that the successor will be the PCI local bus architecture. Most computers made today include both an AT bus for slower devices and a local bus for devices that need better bus performance.

In 1993, Intel and Microsoft introduced a new version of the ISA specification called Plug and Play ISA. Plug and Play ISA enables the operating system to configure expansion boards automatically so that users do not need to fiddle with DIP switches and jumpers.


information highway

A popular buzzword to describe the system of bulletin board services, online services, and other services that enable people to obtain information from telecommunications networks. In the U.S., there is currently a national debate about how to shape and control these avenues of information. Many people believe that the information highway should be designed and regulated by government, just like conventional highway systems. Others argue that government should adopt a more laissez faire attitude. Nearly everyone agrees that accessing the information highway is going to be a normal part of everyday life in the near future.


Infrared Data Association

See IrDA.


init

On Macintoshes an old term (before System 7) for System extensions. See under extension.


Initial Graphics Exchange Specification

See IGES.


initialize

(1) On Apple Macintosh computers, initializing a disk means formatting it.

(2) In programming, initialize means to assign a starting value to a variable.

(3) Initialize can refer to the process of starting up a program or system.


ink-jet printer

A type of printer that works by spraying ionized ink at a sheet of paper. Magnetized plates in the ink's path direct the ink onto the paper in the desired shapes. Ink-jet printers are capable of producing high quality print approaching that produced by laser printers. A typical ink-jet printer provides a resolution of 300 dots per inch, although some newer models offer higher resolutions.

In general, the price of ink-jet printers is lower than that of laser printers. However, they are also considerably slower. Another drawback of ink-jet printers is that they require a special type of ink that is apt to smudge on inexpensive copier paper.

Because ink-jet printers require smaller mechanical parts than laser printers, they are especially popular as portable printers. In addition, color ink-jet printers provide an inexpensive way to print full-color documents.


input

(n) Whatever goes into the computer. Input can take a variety of forms, from commands you enter from the keyboard to data from another computer or device. A device that feeds data into a computer, such as a keyboard or mouse, is called an input device.

(v) The act of entering data into a computer.


input device

Any machine that feeds data into a computer. For example, a keyboard is an input device, whereas a display monitor is an output device. Input devices other than the keyboard are sometimes called alternate input devices. Mice, trackballs, and light pens are all alternate input devices.


input/output

See I/O.


Ins key

The Insert key on Macintosh keyboards.


insert

To place an object between two other objects. Inserting characters, words, paragraphs and documents is common in word processing. Note that insert differs from append, which means to add at the end.

Most computer keyboards have an Insert key, which turns insert mode on and off.


Insert key

A key on computer keyboards that turns the insert mode on and off. The Insert key does not work for all programs, but most word processors and text editors support it.


insert mode

Most text editors and word processors have two text entry modes from which you can choose. In insert mode, the editor inserts all characters you type at the cursor position (or to the right of the insertion point). With each new insertion, the editor pushes over characters to the right of the cursor or pointer to make room for the new character.

If insert mode is turned off, the editor overwrites existing characters instead of inserting the new ones before the old ones. This is often called overstrike (or overwrite) mode. Most PC keyboards have an Ins key that lets you switch back and forth between insert and overwrite modes.

For most programs, the default text entry mode is insert mode.


insertion point

In graphics-based programs, the insertion point is the point where the next characters typed from the keyboard will appear on the display screen. The insertion point is usually represented by a blinking vertical line. You can reposition the insertion point by pressing arrow keys or by moving the I-beam pointer.


Institute of Electrical and Electronic Engineers

See IEEE.


instruction

A basic command. The term instruction is often used to describe the most rudimentary programming commands. For example, a computer's instruction set is the list of all the basic commands in the computer's machine language.


integer

A whole number. The following are integers:

0

1

 -125

144457

In contrast, the following are not integers:

5

-1.0

1.3E4

“string”

The first three are floating-point numbers; the last is a character string.

Integers, floating-point numbers, and character strings constitute the basic data types that most computers support. There are often different sizes of integers available; for example, PCs support short integers, which are 2 bytes, and long integers, which are 4 bytes.


integrated

(1) A popular computer buzzword that refers to two or more components merged together into a single system. For example, any software product that performs more than one task can be described as integrated.

(2) Increasingly, the term integrated software is reserved for applications that combine word processing, database management, spreadsheet functions, and communications into a single package.


integrated circuit (IC)

Another name for a chip, an IC is a small electronic device made out of a semiconductor material. The first integrated circuit was developed in the 1950s by Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Semiconductor.

Integrated circuits are used for a variety of devices, including microprocessors, audio and video equipment, and automobiles. Integrated circuits are often classified by the number of transistors and other electronic components they contain:

SSI (small-scale integration): Up to 100 electronic components per chip

MSI (medium-scale integration): From 100 to 3,000 electronic components per chip

LSI (large-scale integration): From 3,000 to 100,000 electronic components per chip

VLSI (very large-scale integration): From 100,000 to 1,000,000 electronic components per chip

ULSI (ultra large-scale integration): More than 1 million electronic components per chip


Integrated Drive Electronics

See IDE.


integrated services digital network

See ISDN.


Intel microprocessors

Microprocessors made by Intel Corporation form the foundation of all PCs.

Models after the 8086 are often referred to by the last three digits (for example, the 286, 386, and 486). Many of the microprocessors come in different varieties that run at various clock rates. The 80486 architecture, for example, supports clock rates of from 33 to 66 MHz. Because Intel discovered that it couldn't trademark its CPU numbers, it shifted to a naming scheme, starting with the Pentium processors. Intel's latest and sixth-generation chip is called the Pentium Pro.

All Intel microprocessors are backward compatible, which means that they can run programs written for a less powerful processor. The 80386, for example, can run programs written for the 8086, 8088, and 80286. The 80386 and later models, however, offer special programming features not available on previous models. Software written specifically for these processors, therefore, may not run on older microprocessors.

Until the late 80s, Intel was essentially the only producer of PC microprocessors. Increasingly, however, Intel is facing competition from other manufacturers who produce “Intel-compatible” chips. These chips support the Intel instruction set and are often less expensive than Intel chips. In some cases, they also offer better performance.


Intellifont

A scalable font technology that is part of Hewlett-Packard's PCL 5 page description language.


Intelligent Drive Electronics

See IDE.


intelligent terminal

A terminal (monitor and keyboard) that contains processing power. Intelligent terminals include memory and a processor to perform special display operations. In contrast, a dumb terminal has no processing capabilities; it must rely entirely on the central computer. A smart terminal has some processing capabilities, but not as much as an intelligent terminal.


interactive

Accepting input from a human. Interactive computer systems are programs that allow users to enter data or commands. Most popular programs, such as word processors and spreadsheet applications, are interactive.

A noninteractive program is one that, when started, continues without requiring human contact. A compiler is a noninteractive program, as are all batch processing applications.


interface

(n) Something that connects two separate entities. For example, a user interface is the part of a program that connects the computer with a human operator (user).

There are also interfaces to connect programs, to connect devices, and to connect programs to devices. An interface can be a program or a device, such as an electrical connector.

(v) To communicate. For example, two devices that can transmit data between each other are said to interface with each other. This use of the term is scorned by language purists because interface has historically been used as a noun.


interlacing

A display technique that enables a monitor to provide more resolution inexpensively. With interlacing monitors, the electron guns draw only half the horizontal lines with each pass (for example, all odd lines on one pass and all even lines on the next pass). Because an interlacing monitor refreshes only half the lines at one time, it can display twice as many lines per refresh cycle, giving it greater resolution. Another way of looking at it is that interlacing provides the same resolution as noninterlacing, but less expensively.

A shortcoming of interlacing is that the reaction time is slower, so programs that depend on quick refresh rates (animation and video, for example), may experience flickering or streaking. Given two monitors that offer the same resolution, the noninterlacing one will generally be better.


interleaved memory

Main memory divided into two or more sections. The CPU can access alternate sections immediately, without waiting for memory to catch up (through wait states). Interleaved memory is one technique for compensating for the relatively slow speed of dynamic RAM (DRAM). Other techniques include page-mode memory and memory caches.


interleaving

Refers to the way sectors on a disk are organized. In one-to-one interleaving, the sectors are placed sequentially around each track. In two-to-one interleaving, sectors are staggered so that consecutively numbered sectors are separated by an intervening sector.

The purpose of interleaving is to make the disk drive more efficient. The disk drive can access only one sector at a time, and the disk is constantly spinning beneath the read/write head. This means that by the time the drive is ready to access the next sector, the disk may have already spun beyond it. If a data file spans more than one sector and if the sectors are arranged sequentially, the drive will need to wait a full rotation to access the next chunk of the file. If instead the sectors are staggered, the disk will be perfectly positioned to access sequential sectors.

The optimum interleaving factor depends on the speed of the disk drive, the operating system, and the application. The only way to find the best interleaving factor is to experiment with various factors and various applications.


internal cache

Same as primary cache.


internal command

In DOS systems, an internal command is any command that resides in the COMMAND.COM file. This includes the most common DOS commands, such as COPY and DIR. Commands that reside in other COM files, or in EXE or BAT files, are called external commands.


internal font

Same as resident font.


internal modem

A modem that resides on an expansion board that plugs into a computer. In contrast, an external modem is a stand-alone box that attaches to a computer via cables.


International Standards Organization

See ISO.


Internet

A global web connecting more than a million computers. Currently, the Internet has more than 30 million users worldwide, and that number is growing rapidly. More than 70 countries are linked into exchanges of data, news and opinions.

Unlike online services, which are centrally controlled, the Internet is decentralized by design. Each Internet computer, called a host, is independent. Its operators can choose which Internet services to provide to its local users and which local services to make available to the global Internet community. Remarkably, this anarchy by design works exceedingly well.

There are a variety of ways to access the Internet. Most online services, such as CompuServe and Prodigy, offer access to some Internet services. It is also possible to gain access through a commercial Internet provider.


Internet Message Access Protocol

A protocol for retrieving e-mail messages. IMAP is similar to POP%POP but supports some additional features. For example, with IMAP, you can search through your e-mail messages for keywords while the messages are still on mail server.


InterNIC

A collaborative project between AT&T and Network Solutions, Inc. (NSI) supported by the National Science Foundation.  The project current offers the following four services to users of the Internet.

•	InterNIC Directory and Database Services - online white pages directory and directory of publicly accessible databases managed by AT&T.

•	Registration Services - domain name and IP address assignment managed by NSI.

•	Support Services - outreach, education, and information services for the Internet community managed by NSI.

•	Net Scout Services - online publications that summarize recent happenings of interest to Internet users (managed by NSI).


interpreter

A program that executes instructions written in a high-level language. There are two ways to run programs written in a high-level language. The most common is to compile the program; the other method is to pass the program through an interpreter.

An interpreter translates high-level instructions into an intermediate form, which it then executes. In contrast, a compiler translates high-level instructions directly into machine language. Compiled programs generally run faster than interpreted programs. The advantage of an interpreter, however, is that it does not need to go through the compilation stage during which machine instructions are generated. This process can be time-consuming if the program is long. The interpreter, on the other hand, can immediately execute high-level programs. For this reason, interpreters are sometimes used during the development of a program, when a programmer wants to add small sections at a time and test them quickly. In addition, interpreters are often used in education because they allow students to program interactively.

Both interpreters and compilers are available for most high-level languages. However, BASIC and LISP are especially designed to be executed by an interpreter. In addition, page description languages, such as PostScript, use an interpreter. Every PostScript printer, for example, has a built-in interpreter that executes PostScript instructions.


interprocess communication (IPC)

A capability supported by some operating systems that allows one process to communicate with another process. The processes can be running on the same computer or on different computers connected through a network.

IPC enables one application to control another application, and for several applications to share the same data without interfering with one another. IPC is required in all multiprocessing systems, but it is not generally supported by single-process operating systems such as DOS. OS/2 and MS-Windows support an IPC mechanism called DDE.


interrupt

(n) A signal informing a program that an event  has occurred. When a program receives an interrupt signal, it takes a specified action (which can be to ignore the signal). Interrupt signals can cause a program to suspend itself temporarily to service the interrupt.

Interrupt signals can come from a variety of sources. For example, every keystroke generates an interrupt signal. Interrupts can also be generated by other devices, such as a printer, to indicate that some event  has occurred. These are called hardware interrupts. Interrupt signals initiated by programs are called software interrupts.

(v) To send an interrupt signal.


interrupt request line

See IRQ.


intranet

A Web site or group of Web sites belonging to an organization, usually a corporation, accessible only by the organization’s members, employees, or others with authorization.  An intranet’s Web sites look and act just like any other Web sites, but the firewall surrounding an intranet fends off unauthorized access.

Like the Internet itself, intranets are used to share information. Secure intranets are now the fastest-growing segment of the Internet because they are much less expensive to build and manage than private networks based on proprietary protocols.


inverse video

Same as reverse video.


inverted tree

See under tree structure.


invisible file

Same as hidden file.


invocation

The execution of a program or function.


invoke

To activate. One usually speaks of invoking a function or routine in a program. In this sense, the term invoke is synonymous with call.


IP address

An identifier for a computer or device on a TCP/IP network.  Networks using the TCP/IP protocol to route messages based on the IP address of the destination.  The format of an IP address is a 32-bit  numeric address written as four numbers separated by periods.  Each number can be zero to 255.  For example, 1.160.10.240 could be an IP address.

Within an isolated network, you can assign IP addresses at random as long as each one is unique.  However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates.

The four numbers in an IP address are used in different ways to identify a particular network and a host on that network.  The InterNIC Registration Service assigns Internet addresses from the following three classes.

•	Class A - supports 16 million hosts on each of 127 networks

•	Class B - supports 65,000 hosts on each of 16,000 networks

•	Class C - supports 254 hosts on each of 2 million networks

The number of unassigned Internet addresses is running out, so the new Simple Internet Protocol (SIP) will eventually replace the current IP address standard.  SIP uses a 64 bit numeric address to increase the number of available addresses.


IPC

See interprocess communication.


IrDA

Short for Infrared Data Association, a group of device manufacturers that developed a standard for transmitting data via infrared light waves. Increasingly, computers and other devices (such as printers) come with IrDA ports. This enables you to transfer data from one device to another without any cables. For example, if both your laptop computer and printer have IrDA ports, you can simply put your computer in front of the printer and output a document, without needing to connect the two with a cable.

IrDA ports support roughly the same transmission rates as traditional parallel ports. The only restrictions on their use is that the two devices must be within a few feet of each other and there must be a clear line of sight between them.


IRMA board

A popular expansion board for PCs and Macintoshes that enables these personal computers to emulate IBM 3278 and 3279 mainframe terminals. In other words, personal computers with IRMA boards can function as both stand-alone computers and as terminals connected to a mainframe computer. IRMA boards are made by a company called DCA.


IRQ

Abbreviation of interrupt request line, and pronounced I-R-Q. IRQs are hardware lines over which devices can send interrupt signals to the microprocessor. When you add a new device to a PC, you often need to set its IRQ number by setting a DIP switch. This specifies which interrupt line the device may use. IRQ conflicts are a common problem when adding expansion boards, but the new Plug and Play ISA specification may remove this headache.


ISA

Abbreviation of Industry Standard Architecture and pronounced eye-sa. See under Industry Standard Architecture (ISA) bus.


ISA bus

See under Industry Standard Architecture (ISA) bus.


ISDN

Abbreviation of integrated services digital network, an international communications standard for sending voice, video, and data over digital telephone lines. ISDN requires special metal wires and supports data transfer rates of 64,000 bits per second.

The original version of ISDN employs baseband transmission. Another version, called B-ISDN, uses broadband transmission and is able to support transmission rates of 1.5 million bits per second. B-ISDN requires fiber optic cables.


ISO

Acronym for International Standards Organization. Founded in 1946, ISO is an international organization composed of national standards bodies from over 75 countries. For example, ANSI (American National Standards Institute) is a member of ISO. ISO has defined a number of important computer standards, the most significant of which is perhaps OSI (Open Systems Interconnection), a standardized architecture for designing networks.


italic

In typography, italic refers to fonts with characters slanted to the right. An italic font, however, often includes one or more character shapes, such as the a and the f, that differ from those in the roman font of the same family.


iteration

A single pass through a group of instructions. Most programs contain loops of instructions that are executed over and over again. The computer iterates through the loop, which means that it repeatedly executes the loop.


jaggies

Stairlike lines that appear where there should be smooth straight lines or curves. Jaggies can occur for a variety of reasons, the most common being that the output device (display monitor or printer) does not have enough resolution to portray a smooth line. In addition, jaggies often occur when a bit-mapped image is converted to a different resolution. This is one of the advantages vector graphics has over bit-mapped graphics—the output looks the same regardless of the resolution of the output device.

The effect of jaggies can be reduced somewhat by a graphics technique known as antialiasing. Antialiasing smoothes out jagged lines by surrounding the jaggies with shaded pixels. In addition, some printers can reduce jaggies with a technique known as smoothing.


Java

A high level programming language developed by Sun Microsystems. Java is an object-oriented language similar to C++, but simplified to eliminate language features that cause common programming errors. Java source code is compiled into a format called byte-code, which can then be executed by a Java interpreter. Compiled Java code can run on most computers because Java interpreters exist for most operating systems, including UNIX, the Macintosh OS, and Windows.

Java is a general purpose programming language with a number of features that make the language well suited for use on the World Wide Web.  Small Java applications are called Java applets and can be downloaded from a Web server and run on your computer by a Java-compatible Web browser, such as Netscape Navigator or Microsoft Internet Explorer. Microsoft has stated that it intends to include a Java interpreter in future versions of Windows, which will enable users to execute Java applets directly from the operating system.


JavaScript

A scripting language developed by Netscape to enable Web authors to design interactive sites. Although it shares many of the features and structures of the full Java language, it was developed independently. Javascript can interact with HTML source code, enabling Web authors to spice up their sites with animations and dynamic content. JavaScript is endorsed by a number of software companies and is an open language that anyone can use without purchasing a license. It is supported by recent browsers from Netscape and Microsoft.


job

A task performed by a computer system. For example, printing a file is a job. Jobs can be performed by a single program or by a collection of programs.


join

In relational databases, a join operation is a query that retrieves data from two separate databases. The two databases must be joined by at least one common field. That is, the join field is a member of both databases.


Joint Photographic Experts Group

See JPEG.


joystick

A lever that moves in all directions and controls the movement of a pointer or some other display symbol. A joystick is similar to a mouse, except that with a mouse the cursor stops moving as soon as you stop moving the mouse. With a joystick, the pointer continues moving in the direction the joystick is pointing. To stop the pointer, you must return the joystick to its upright position. Most joysticks include two buttons called triggers.

Joysticks are used mostly for computer games, but they are also used occasionally for CAD/CAM systems and other applications.


JPEG

Short for Joint Photographic Experts Group, and pronounced jay-peg. JPEG is a lossy compression technique for color images. Although it can reduce files sizes to about 5% of their normal size, some detail is lost in the compression.


jumper

A metal bridge that closes an electrical circuit . Typically, a jumper consists of a plastic plug that fits over a pair of protruding pins. Jumpers are sometimes used to configure expansion boards. By placing a jumper plug over a different set of pins, you can change a board's parameters.


justification

Alignment of text along a margin. For example, the following is both left- and right-justified:

This text is left- and right-justified because the left and right margins are aligned. Note, however, that the justification does not look very good because the text is printed with a fixed-pitch font.

The text above looks a bit funny because there are wide gaps between some letters but not between others. To produce good-looking justification, the word processor and printer must be capable of microspacing; that is, they must be able to separate letters by less than a full space. In addition, justified text always looks better when a proportional font is used. For example:

This text is left- and right-justified, and microspacing is in effect. Compare this to the previous example, which did not use microspacing.

Vertical justification refers to adjusting the vertical space between lines so that columns and pages have an even bottom margin. One vertical justification technique, called feathering, inserts an even amount of space between each line so that the page or column has a specified vertical length.


justify

In word processing, to align text along the left and right margins.


K

(1) Short for kilo or kilobyte. See under kilobyte.


KB

Short for kilobyte (1,024 bytes).


Kbps

Short for kilobits per second, a measure of data transfer speed. Modems, for example, are measured in Kbps.


Kermit

A file-transfer protocol developed at Columbia University. Kermit can be used by modems and communications software to send files over telephone lines. Although it is a relatively slow protocol, Kermit is noted for its transmission accuracy. Kermit is not in the public domain, but Columbia University allows people to use the protocol for free, so almost all communications products support it.

There are actually two versions of Kermit, the original version and a later version called Super Kermit. Unlike standard Kermit, Super Kermit supports full-duplex transmission, which makes it much faster.

Other file-transfer protocols used by slow- to medium-speed modems include Xmodem and Zmodem.


kerning

In typography, kerning refers to adjusting the space between characters, especially by placing two characters closer together than normal. Kerning makes certain combinations of letters, such as WA, MW, TA, and VA, look better.

Only the most sophisticated word processors and desktop publishing systems perform kerning. Normally, you can activate or deactivate kerning for particular fonts.


key

(1) A button on a keyboard.

(2) In database management systems, a key is a field that you use to sort data. It can also be called a key field, sort key, index, or key word. For example, if you sort records by age, then the age field is a key. Most database management systems allow you to have more than one key so that you can sort records in different ways.

(3) A password or table needed to decipher encoded data.


key field

See under key.


keyboard

The set of typewriter-like keys that enables you to enter data into a computer. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys. The keys on computer keyboards are often classified as follows:

alphanumeric keys—letters and numbers

punctuation keys—comma, period, semicolon, and so on.

special keys—function keys, control keys, arrow keys, Caps Lock key, and so on.

The standard layout of letters, numbers, and punctuation is known as a QWERTY keyboard because the first five keys on the top row of letters spell QWERTY. The QWERTY keyboard was designed in the 1800s for mechanical typewriters and was actually designed to slow typists down to avoid jamming the keys. Another keyboard design, which has letters positioned for speed typing, is the Dvorak keyboard.

There is no standard computer keyboard, although many manufacturers imitate the keyboards of PCs. There are actually three different PC keyboards: the original PC keyboard, with 84 keys; the AT keyboard, also with 84 keys; and the enhanced keyboard, with 101 keys. The three differ somewhat in the placement of function keys, the Control key, the Return key, and the Shift keys.

In addition to these keys, IBM keyboards contain the following keys: Page Up, Page Down, Home, End, Insert, Pause, Num Lock, Scroll Lock, Break, Caps Lock, Print Screen.

There are several different types of keyboards for the Apple Macintosh. All of them are called ADB keyboards because they connect to the Apple Desktop bus (ADB). The two main varieties of Macintosh keyboards are the standard keyboard and the extended keyboard, which has 15 additional special-function keys.


keyboard buffer

See under buffer.


keyboard template

See under template.


keypad

See under numeric keypad.


keystroke

The pressing of a key. The efficiency of software programs is sometimes measured by the number of keystrokes it requires to perform a specific function. The fewer the keystrokes, claim some software producers, the faster and more efficient the program. The number of keystrokes, however, is generally less important than other characteristics of the software.


keyword

(1) In text editing and database management systems, a keyword is an index entry that identifies a specific record or document.

(2) In programming, a keyword is a word that is reserved by a program because the word has a special meaning. Keywords can be commands or parameters. Every programming language has a set of keywords that cannot be used as variable names. Keywords are sometimes called reserved names.


killer app

See under app.


kilobyte

In decimal systems, kilo stands for 1,000, but in binary  systems, a kilo is 1,024 (2 to the 10th power). Technically, therefore, a kilobyte is 1,024 bytes, but it is often used loosely as a synonym for 1,000 bytes. For example, a computer that has 256K main memory can store approximately 256,000 bytes (or characters) in memory at one time.

A megabyte is 220 (approximately 1 million) and a gigabyte is 230 (approximately 1 billion).

In computer literature, kilobyte is usually abbreviated as K or Kb. To distinguish between a decimal K (1,000) and a binary  K (1,024), the IEEE has suggested following the convention of using a small k for a decimal kilo and a capital K for a binary  kilo, but this convention is by no means strictly followed.


kludge

Pronounced klooj, a derogatory term that refers to a poor design. Like hacks, kludges use nonstandard techniques. But, whereas a hack can connote a clever solution to a problem, a kludge always implies that the solution is inelegant.


L1 cache

Short for Level 1 cache, a memory cache built into the microprocessor. See under cache.


L2 cache

Short for Level 2 cache, an external cache. See under cache.


label

(1) A name.

(2) For mass storage devices, a label is the name of a storage volume. It is sometimes referred to as a volume label. Each operating system has its own set of rules for labeling volumes. The label provides a mnemonic name that indicates what type of information is stored on the media.

(3) In spreadsheet programs, a label is any descriptive text placed in a cell.

(4) In programming languages, a label refers to a particular location in a program, usually a particular line of source code.

(5) The term label is also commonly used to mean a small, sticky piece of paper that you can place on an object to identify it. For example, you can paste labels on floppy disks to indicate what data is stored on them.


LAN

See local-area network.


landscape

In word processing and desktop publishing, the terms portrait and landscape refer to whether the document is oriented vertically or horizontally. A page with landscape orientation is wider than it is tall.

Not all printers are capable of generating text in landscape mode. Of those that are, some require special landscape versions of their fonts; others can rotate the standard portrait fonts 90 degrees.

Orientation is also a characteristic of monitors.


language

A system for communicating. Written languages use symbols (that is, characters) to build words. The entire set of words is the language's vocabulary. The ways in which the words can be meaningfully combined is defined by the language's syntax and grammar. The actual meaning of words and combinations of words is defined by the language's semantics.

In computer science, human languages are known as natural languages. Unfortunately, computers are not sophisticated enough to understand natural languages. As a result, we must communicate with computers using special computer languages. There are many different classes of computer languages, including machine languages, programming languages, and fourth-generation languages.


laptop computer

A small, portable computer—small enough that it can sit on your lap. Nowadays, laptop computers are more frequently called notebook computers.


large-scale integration (LSI)

Refers to the placement of thousands of electronic components on a single integrated circuit.


laser printer

A type of printer that utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. This is also the way copy machines work.

Because an entire page is transmitted to a drum before the toner is applied, laser printers are sometimes called page printers. There are two other types of page printers that fall under the category of laser printers even though they do not use lasers at all. One uses an array of LEDs to expose the drum, and the other uses LCDs. Once the drum is charged, however, they both operate like a real laser printer.

One of the chief characteristics of laser printers is their resolution—how many dots per inch (dpi) they lay down. The available resolutions range from 300 dpi at the low end to 1,200 dpi at the high end. By comparison, offset printing usually prints at 1,200 or 2,400 dpi. Some laser printers achieve higher resolutions with special techniques known generally as resolution enhancement.

In addition to the standard monochrome laser printer, which uses a single toner, there also exist color laser printers that use four toners to print in full color. Color laser printers tend to be about five to ten times as expensive as their monochrome siblings.

Laser printers produce very high-quality print and are capable of printing an almost unlimited variety of fonts. Most laser printers come with a basic set of fonts, called internal or resident fonts, but you can add additional fonts in one of two ways:

font cartridges: Laser printers have slots in which you can insert font cartridges, ROM boards on which fonts have been recorded. The advantage of font cartridges is that they use none of the printer's memory.

soft fonts: All laser printers come with a certain amount of RAM memory, and you can usually increase the amount of memory by adding memory boards in the printer's expansion slots. You can then copy fonts from a disk to the printer's RAM. This is called downloading fonts. A font that has been downloaded is often referred to as a soft font, to distinguish it from the hard fonts available on font cartridges. The more RAM a printer has, the more fonts that can be downloaded at one time.

In addition to text, laser printers are very adept at printing graphics. However, you need significant amounts of memory in the printer to print high-resolution graphics. To print a full-page graphic at 300 dpi, for example, you need at least 1 MB (megabyte) of printer RAM. For a 600-dpi graphic, you need at least 4 MB RAM.

Because laser printers are nonimpact printers, they are much quieter than dot-matrix or daisy-wheel printers. They are also relatively fast, although not as fast as some dot-matrix printers. The speed of laser printers ranges from about 4 to 20 pages of text per minute (ppm). A typical rate of 6 ppm is equivalent to about 40 characters per second (cps).

Laser printers are controlled through page description languages (PDLs). There are two de facto standards for PDLs:

PCL: Hewlett-Packard (HP) was one of the pioneers of laser printers and has developed a Printer Control Language (PCL) to control output. There are several versions of PCL, so a printer may be compatible with one but not another. In addition, many printers that claim compatibility cannot accept HP font cartridges.

PostScript: This is the de facto standard for Apple Macintosh printers and for all desktop publishing systems.

Most software can print using either of these PDLs. PostScript tends to be a bit more expensive, but it has some features that PCL lacks and it is the standard for desktop publishing. Some printers support both PCL and PostScript.


LaserWriter

A family of Apple laser printers designed to run off a Macintosh computer.


launch

To start a program.


LAWN

See local-area wireless network.


layout

(1) In word processing and desktop publishing, layout refers to the arrangement of text and graphics. The layout of a document can determine which points are emphasized, and whether the document is aesthetically pleasing.

While no computer program can substitute for a professional layout artist, a powerful desktop publishing system can make it easier to lay out professional-looking documents. A WYSIWYG aids layout considerably because it allows you to lay out a document on the display screen and see what it will look like when printed.

(2) In database management systems, layout refers to the way information is displayed. You can change the layout by selecting different fields.


LCD

Abbreviation of liquid crystal display, a type of display used in digital watches and many portable computers. LCD displays utilize two sheets of polarizing material with a liquid crystal solution between them. An electric current passed through the liquid causes the crystals to align so that light cannot pass through them. Each crystal, therefore, is like a shutter, either allowing light to pass through or blocking the light.

Monochrome LCD images usually appear as blue or dark gray images on top of a grayish-white background. Color LCD displays use two basic techniques for producing color: Passive matrix is the less expensive of the two technologies, but its colors are not particularly sharp and it has slow reaction times. The other technology, called thin film transistor (TFT) or active-matrix, produces color images that are as sharp as traditional CRT displays, but the technology is expensive.

Most LCD screens used in notebook computers are backlit to make them easier to read in bright environments.


LCD printer

A type of printer similar to a laser printer. Instead of using a laser to create an image on the drum, however, it shines a light through a liquid crystal panel. Individual pixels in the panel either let the light pass or block the light, thereby creating an image composed of dots on the drum.

Liquid crystal shutter printers produce print quality equivalent to that of laser printers.


leader

Rows of dots, dashes or other characters that lead your eye from one text element to another. Leaders are used commonly in Tables of contents. For example:

Chapter 5…………………………….233


leading

Pronounce ledd-ing, a typographical term that refers to the vertical space between lines of text. The word derives from the fact that typographers once used thin strips of lead to separate lines. Now, the leading value also includes the size of the font. For example, 10-point text with 2 points of spacing between lines would mean a leading of 12 points.

Many word processors and all desktop publishing systems allow you to specify the leading. In addition, some systems automatically adjust leading so that columns and pages have even bottom margins. This feature is called vertical justification.

Leading is also called line spacing.


leading zero

A zero that appears in the leftmost digit(s) of a number. Many programs that display numbers in columns allow you to specify whether the number should be preceded with spaces or leading zeros, as shown below.

leading zeros	spaces
0003.45	3.45
0148.70	148.70


leaf

Items at the very bottom of a hierarchical tree structure. In hierarchical file systems, files are leaves because they can have nothing below them. Directories, on the other hand, are nodes.


learn mode

A mode in which a program learns. The term is usually used to describe a process of defining macros. Once you switch the program into learn mode, it will record all subsequent keystrokes you make. You can then assign these keystrokes to a function key to create a macro.


leased line

A permanent telephone connection between two points set up by a telecommunications common carrier.  Typically, leased lines are used by businesses to connect geographically distant offices. Unlike normal dial-up connections, a leased line is always active. The fee for the connection is a fixed monthly rate. The primary factors affecting the monthly fee are distance between end points and the speed of the circuit.  Because the connection doesn't carry anybody else's communications, the carrier can assure a given level of quality.

For example, a T-1 channel is a type of leased line that provides a maximum transmission speed of 1.554 megabits per second.  You can divide the connection into different lines for data and voice communication or use the channel for one high speed data circuit.  Dividing the connection is called multiplexing.

Increasingly, leased lines are being used by companies, and even individuals, for Internet access because they afford faster data transfer rates and are cost-effective if the Internet is used heavily.


LED

Abbreviation of light emitting diode, an electronic device that lights up when electricity is passed through it. LEDs are usually red. They are good for displaying images because they can be relatively small, and they do not burn out. However, they require more power than LCDs.


LED printer

See under laser printer.


left justify

To align text along the left margin. Left-justified text is the same as flush-left text.


legend

In presentation graphics, text that describes the meaning of colors and patterns used in the chart.


letter quality (LQ)

Refers to print that has the same quality as that produced by a typewriter. Computer printers are sometimes divided into two classes: those that produce letter-quality type, such as laser, ink-jet, and daisy-wheel printers; and those that do not, including most dot-matrix printers.

The term letter quality is really something of a misnomer now, because laser printers produce print that is considerably better than that produced by a typewriter.

Many dot-matrix printers produce a high-quality print known as near letter quality. You have to look closely to see that the print is not really letter quality. A lower classification of print quality is called draft quality.


Level 2 cache

Same as external cache. See under cache.


library

(1) A collection of files.

(2) In programming, a library is a collection of precompiled routines that a program can use. The routines, sometimes called modules, are stored in object format. Libraries are particularly useful for storing frequently used routines because you do not need to explicitly link them to every program that uses them. The linker automatically looks in libraries for routines that it does not find elsewhere. In MS-Windows environments, library files have a .DLL extension.


light bar

On a display screen, a highlighted region that indicates a selected component in a menu. The light bar can be produced by using a different color or by reversing the image so that black-on-white text becomes white-on-black.


light pen

An input device that utilizes a light-sensitive detector to select objects on a display screen. A light pen is similar to a mouse, except that with a light pen you can move the pointer and select objects on the display screen by directly pointing to the objects with the pen.


light-emitting diode

See LED.


LIM memory

A technique for adding memory to DOS systems. LIM memory lets you exceed the 1MB (megabyte) memory limit imposed by DOS. The name derives from the initials of the three companies that designed the technique—Lotus, Intel, and Microsoft—and is sometimes referred to as LIM 4.0, which is its official name.

LIM memory has been largely superseded by extended memory.


line

(1) A hardware circuit connecting two devices.

(2), In programming, a single program statement.


line art

A type of graphic consisting entirely of lines, without any shading. Most art produced on computers is not line art because the computer makes it so easy to add subtle shadings.


line editor

A primitive type of editor that allows you to edit only one line of a file at a time.


line feed

Often abbreviated LF, a line feed is a code that moves the cursor on a display screen down one line. In the ASCII character set, a line feed has a decimal value of 10.

On printers, a line feed advances the paper one line. Some printers have a button labeled LF that executes a line feed when pressed. (Note, however, that the printer must be in off-line mode to execute a line feed.)


line graph

A type of graph that highlights trends by drawing connecting lines between data points. Compare with bar chart and pie graph.


line printer

A high-speed printer capable of printing an entire line at one time. A fast line printer can print as many as 3,000 lines per minute. The disadvantages of line printers are that they can print only one font, they cannot print graphics, the print quality is low, and they are very noisy.


line spacing

See under leading.


lines per inch

See under halftone.


link

(v) (1) To bind together.

(2) In programming, the term link refers to execution of a linker.

(3) To paste a copy of an object into a document in such a way that it retains its connection with the original object. Updates to the original object can be reflected in the duplicate by updating the link.

(4) In spreadsheet programs, linking refers to the ability of a worksheet to take its data for particular cells from another worksheet. Two or more files are thus linked by common cells.

(n) (1) In communications, a link is a line or channel over which data is transmitted.

(2) In data management systems, a link is a pointer to another record. You can connect one or more records by inserting links into them.

(3) In some operating systems (UNIX, for example), a link is a pointer to a file. Links make it possible to reference a file by several different names and to access a file without specifying a full path.

(4) In hypertext systems, such as the World Wide Web, a link is a reference to another document. Such links are sometimes called hot links because they take you to other document when you click on them.


link edit

To run a linker.


linker

Also called link editor and binder, a linker is a program that combines object modules to form an executable program. Many programming languages allow you to write different pieces of code, called modules, separately. This simplifies the programming task because you can break a large program into small, more manageable pieces. Eventually, though, you need to put all the modules together. This is the job of the linker.

In addition to combining modules, a linker also replaces symbolic addresses with real addresses. Therefore, you may need to link a program even if it contains only one module.


Lino

Short for Linotronic, a type of imagesetter. Although Linotronic is a brand name, the terms Lino and Linotronic are often used to refer to any imagesetter.


Linotronic

A common type of high-quality printer, called an imagesetter, capable of printing at resolutions of up to 2540 dots per inch. Linotronic printers are too expensive for homes or most offices, but you can obtain Linotronic output by taking a PostScript file to a Service Bureau.


liquid crystal display

See LCD.


liquid crystal shutter printer

See under LCD printer.


LISP

Acronym for list processor, a high-level programming language especially popular for artificial intelligence applications. LISP was developed in the early 1960s by John McCarthy at MIT.


list

(v) To display data in an ordered format. For example, the LIST command in BASIC displays lines of a program.

(n) Any ordered set of data.


listing

A printout of text, usually a source program.


load

(1) To install. For example, to load a disk means to mount it in a disk drive.

(2) To copy a program from a storage device into memory. Every program must be loaded into memory before it can be executed. Usually the loading process is performed invisibly by a part of the operating system called the loader. You simply enter the name of the program you want to run, and the operating system loads it and executes it for you.

(3) In programming, load means to copy data from main memory into a data register.

(4) In networking, load refers to the amount of data (traffic) being carried by the network.


loader

An operating system utility that copies programs from a storage device to main memory, where they can be executed. In addition to copying a program into main memory, the loader can also replace virtual addresses with physical addresses.

Most loaders are invisible: that is, you cannot directly execute them, but the operating system uses them when necessary.


local

In networks, local refers to files, devices, and other resources at your workstation. Resources located at other nodes on the networks are remote.


local bus

A data bus that connects directly, or almost directly, to the microprocessor. Although local buses can support only a few devices, they provide very fast throughput. Most modern PCs include both a local bus, for video data, as well as a more general expansion bus for other devices that do not require such fast data throughput.


local echo

Same as half duplex.


local-area network (LAN)

A computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN) .

Most LANs connect workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs, but it is also able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.

There are many different types of LANs, token-ring networks, Ethernets, and ARCnets being the most common for PCs. Most Apple Macintosh networks are based on Apple's AppleTalk network system, which is built into Macintosh computers.

The following characteristics differentiate one LAN from another:

topology: The geometric arrangement of devices on the network. For example, devices can be arranged in a ring or in a straight line.

protocols: The rules and encoding specifications for sending data. The protocols also determine whether the network uses a peer-to-peer or client/server architecture.

media: Devices can be connected by twisted-pair wire, coaxial cables, or fiber optic cables. Some networks do without connecting media altogether, communicating instead via radio waves.

LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.


local-area wireless network (LAWN)

A type of local-area network that uses high-frequency radio waves rather than wires to communicate between nodes.


LocalTalk

The cabling scheme supported by the AppleTalk network protocol for Macintosh computers. Most local-area networks that use AppleTalk, such as TOPS, also conform to the LocalTalk cable system. Such networks are sometimes called LocalTalk networks.

Although LocalTalk networks are relatively slow, they are popular because they are easy and inexpensive to install and maintain. An alternative cabling scheme that is faster is Ethernet.


lock

(1) To make a file or other piece of data inaccessible. File locking is a critical component of all multi-user computer systems, including local-area networks. When users share files, the operating system must ensure that two or more users do not attempt to modify the same file simultaneously. It does this by locking the file as soon as the first user opens it. All subsequent users may read the file, but they cannot write to it until the first user is finished.

In addition to file locking, many database management systems support record locking, in which a single record, rather than an entire file, is locked. This enables different users to access different records within the same file without interfering with one another.

(2) In Macintosh environments, locking a diskette means write-protecting it.


log in

Same as log on.


log off

Same as log out.


log on

To make a computer system recognize you so that you can begin a computer session. Most personal computers have no log-on procedure—you just turn the machine on and begin working. For larger systems and networks, however, you usually need to enter a username and password before the computer system will allow you to execute programs.


log out

To end a session at the computer. For personal computers, you can log out simply by exiting applications and turning the machine off. On larger computers and networks, where you share computer resources with other users, there is generally an operating system command that lets you log off.


logical

Refers to a user's view of the way data or systems are organized. The opposite of logical is physical, which refers to the real organization of a system. For example, a logical description of a file is that it is a collection of data stored together. This is the way files appear to users. Physically, however, a single file can be divided into many pieces scattered across a disk.


logical operator

Same as Boolean operator.


look-and-feel

Refers to the general appearance and operation of a user interface. This is a hot legal issue because some software companies are claiming that competitors who copy the look-and-feel of their products are infringing on their copyright protection. To date, the courts have not ruled definitively on this matter.


loop

In programming, a loop is a series of instructions that is repeated until a certain condition is met. Each pass through the loop is called an iteration. Loops constitute one of the most basic and powerful programming concepts.


lossless compression

Refers to data compression techniques in which no data is lost. The PKZIP compression technology is an example of lossless compression. For most types of data, lossless compression techniques can reduce the space needed by only about 50%. For greater compression, one must use a lossy compression technique.


lossy compression

Refers to data compression techniques in which some amount of data is lost. Lossy compression technologies attempt to eliminate redundant or unnecessary information. Most video compression technologies, such as JPEG, use a lossy technique.


Lotus 1-2-3

A spreadsheet program designed for IBM-compatible personal computers by Lotus Corporation in 1982. Lotus 1-2-3 was the first publicly available program to combine graphics, spreadsheet functions and data management (three functions, hence the name). Its relative ease of use and flexibility made it an enormous success and contributed to the acceptance of personal computers in business.


low resolution

See under resolution.


low-level format

Hard disks must be formatted twice before they can be used. The first format, called a low-level or physical format, sets the interleave factor and prepares the disk for a particular type of disk controller. This is generally performed at the factory.


low-level language

A machine language or an assembly language. Low-level languages are closer to the hardware than are high-level programming languages, which are closer to human languages.


lowercase

Small letters, as opposed to capital letters. The word yes, for example, is in lowercase, while the word YES is in uppercase. For many programs, this distinction is very important. Programs that distinguish between lowercase and uppercase are said to be case sensitive.


LPT

A name frequently used by operating systems to identify a printer. Although LPT originally stood for line printer terminal, it is now used more generally to identify any type of printer.


LQ

See letter quality.


LSI

See large-scale integration.


luggable

Same as transportable.


M

Abbreviation for mega or megabyte.


Mac

Short for Macintosh computer.


machine address

Same as absolute address.


machine code

See under machine language.


machine dependent

Refers to a software application that runs only on a particular model of computer. Programs that run on a variety of computers are called machine independent.

Almost all programs have some machine dependencies (that is, they run somewhat differently on different computers), but the degree of independence can vary widely. Machine-independent programs give you more flexibility: if you buy a new computer, you can continue using the same software package instead of learning a new one. On the other hand, machine-dependent programs often take advantage of special hardware features of a particular computer, making the programs faster.

Another term for machine dependent is device dependent, but whereas machine dependent usually refers to the computer, device dependent can refer to a dependency on any device, like a printer.


machine independent

Able to run on a variety of computers.


machine language

The lowest-level programming language. Machine languages are the only languages understood by computers. While easily understood by computers, machine languages are almost impossible for humans to use because they consist entirely of numbers. Programmers, therefore, use either a high-level programming language or an assembly language. An assembly language contains the same instructions as a machine language, but the instructions and variables have names instead of being just numbers.

Programs written in high-level languages are translated into assembly language or machine language by a compiler. Assembly language programs are translated into machine language by a program called an assembler.

Every CPU has its own unique machine language. Programs must be rewritten or recompiled, therefore, to run on different types of computers.

See assembler, assembly language, compiler, CPU, high-level language, low-level language, programming language.


machine readable

In a form that a computer can accept. Machine-readable data includes files stored on disk or tape, or data that comes from a device connected to a computer. Even typewritten pages can be considered machine-readable if you have an optical character recognition (OCR) system.


Macintosh computer

A popular model of computer made by Apple Computer. Introduced in 1984, the Macintosh features a graphical user interface (GUI) that utilizes windows, icons, and a mouse to make it relatively easy for novices to use the computer productively. Rather than learning a complex set of commands, you need only point to a selection on a menu and click a mouse button.

Moreover, the GUI is embedded into the operating system. This means that all applications that run on a Macintosh computer have a similar user interface. Once a user has become familiar with one application, he or she can learn new applications relatively easily.

The Macintosh family of computers is not compatible with the IBM family of personal computers. They have different microprocessors and different file formats. This makes it difficult (though not impossible) to share data between the two types of computers.

Since the Macintosh interface's arrival on the marketplace and its enthusiastic acceptance by customers, numerous software producers have produced similar interfaces. For example, Microsoft offers a Mac-like GUI for PCs called Windows.

There are many different Macintosh models, with varying degrees of speed and power. All models are available in many different configurations—different monitors, disk drives, and memory. All older Macintosh computers use a microprocessor from the Motorola 68000 family, but in 1994 Apple switched to the PowerPC microprocessor. PowerMacs can also run programs written for the Motorola processors.


macro

(1) A symbol, name, or key that represents a list of commands, actions, or keystrokes. Many programs allow you to create macros so that you can enter a single character or word to perform a whole series of actions. Suppose, for example, that you are editing a file and want to indent every third line five spaces. If your word processor supports macros, you can create one that consists of the following keystrokes:

Move Cursor to Beginning of Line

Move Cursor Down 1 Line

Move Cursor Down 1 Line

Move Cursor Down 1 Line

Insert 5 Spaces

Now you can enter the name of the macro, and the word processor will perform all these commands at once.

You can also use macros to enter words or phrases that you use frequently. For example, you could define a macro to contain all the keystrokes necessary to begin a letter—your name, address, and a code that inserts the current date. Then, whenever you write a letter, you just press the macro key to include the letter header.

In a way, macros are like simple programs or batch files. Some applications support sophisticated macros that even allow you to use variables and flow control structures such as loops.

(2) In dBASE programs, a macro is a variable that points to another variable where the data is actually stored. In most other applications, this would be called a link.


magnetic disk

See under disk.


magnetic tape

See under tape.


magneto-optical (MO) drive

A type of disk drive that combines magnetic disk technologies with CD-ROM technologies. Like magnetic disks, MO disks can be read and written to. And like floppy disks, they are removable. However, their storage capacity can be more than 200 megabytes, much greater than magnetic floppies. In terms of data access speed, they are faster than floppies and CD-ROMs, but not as fast as hard disk drives.


mail

See e-mail.


mail merge

A feature supported by many word processors that enables you to generate form letters. To use a mail-merge system, you first store a set of information, like a list of names and addresses, in one file. In another file, you write a letter, substituting special symbols in place of names and addresses (or whatever other information will come from the first file). For example, you might write:

Dear NAME:

Our records show that your address is:

STREET

CITY, STATE ZIP

If this is incorrect, . . .

When you execute the merge command, the word processor automatically generates letters by replacing symbols (NAME, STREET, CITY, STATE, and ZIP) in the second file with the appropriate data from the first file

The power and flexibility of mail merge systems varies considerably from one word processor to another. Some word processors support a full set of logical operators that enable you to specify certain conditions under which information should be merged. Also, some merge systems allow you to merge data from several files at once.

Mail merge is sometimes called print merge.


mailbox

An area in memory or on a storage device where e-mail is placed. In e-mail systems, each user has a private mailbox. When the user receives e-mail, the mail system automatically puts it in the mailbox.

The mail system allows you to scan mail that is in your mailbox, copy it to a file, delete it, print it, or forward it to another user. If you want to save mail, it is a good idea to copy it to a file, because files tend to be more stable than mailboxes.


main memory

Refers to physical memory that is internal to the computer. The word main is used to distinguish it from external mass storage devices such as disk drives. Another term for main memory is RAM.

The computer can manipulate only data that is in main memory. Therefore, every program you execute and every file you access must be copied from a storage device into main memory. The amount of main memory on a computer is crucial because it determines how many programs can be executed at one time and how much data can be readily available to a program.

Because computers often have too little main memory to hold all the data they need, computer engineers invented a technique called swapping, in which portions of data are copied into main memory as they are needed. Swapping occurs when there is no room in memory for needed data. When one portion of data is copied into memory, an equal-sized portion is copied (swapped) out to make room. Another technique, called virtual memory, enables a computer to access larger amounts of data than main memory can hold at one time, but it is a relatively slow process. Therefore, the more memory a computer has and the more it can avoid swapping, the faster it will be able to execute large programs.

Now, most PCs come with a minimum of 4 megabytes of main memory. This is adequate for some applications, but you may need more memory to run sophisticated applications, particularly those that include graphics. You can usually increase the amount of memory by inserting extra memory in the form of chips or memory expansion boards.


mainframe

A very large and expensive computer capable of supporting hundreds, or even thousands, of users simultaneously. In the hierarchy that starts with a simple microprocessor (in watches, for example) at the bottom and moves to supercomputers at the top, mainframes are just below supercomputers. In some ways, mainframes are more powerful than supercomputers because they support more simultaneous programs. But supercomputers can execute a single program faster than a mainframe. The distinction between small mainframes and minicomputers is vague, depending really on how the manufacturer wants to market its machines.

Unisys and IBM are the largest manufacturers of mainframes.


male connector

See under connector.


management information system

See under MIS.


manual recalculation

In spreadsheet programs, a mode in which formulas are not recalculated until you explicitly (manually) run the recalculation function. Compare with automatic recalculation, where cells containing formulas are automatically reevaluated whenever necessary.


map

(n) A file showing the structure of a program after it has been compiled. The map file lists every variable in the program along with its memory address. This information is useful for debugging purposes. Normally a compiler will not produce a map file unless you explicitly ask for it by specifying the appropriate compiler option.

(v) (1) To make logical connections between two entities. Because programs cannot translate directly from human concepts to computer numbers, they translate incrementally through a series of layers. Each layer contains the same amount of information as the layer above but in a form somewhat closer to the form that the computer understands. This activity of translating from one layer to another is called mapping.

The term map is often used to describe programming languages. For example, C is an efficient programming language because it maps well onto the machine language. What this means is that it is relatively easy to translate from the C language to machine languages.

(2) To copy a set of objects from one place to another while preserving the objects' organization. For example, when loaded, programs on a disk are mapped into memory. Graphics images in memory are mapped onto a display screen.


map file

See under map.


MAPI

Abbreviation of Messaging Application Programming Interface, a system built into Microsoft Windows that enables different e-mail applications to work together to distribute mail. As long as both applications are MAPI-enabled, they can share mail messages with each other.


margins

In word processing, the strips of white space around the edge of the paper. Most word processors allow you to specify the widths of margins. The wider the left and right margins, the narrower the page. The wider the top and bottom margins, the shorter the page.

If your word processor performs word wrap, it will automatically adjust the length of the lines when you change the widths of the margins.


mask

A filter that selectively includes or excludes certain values. For example, when defining a database field, it is possible to assign a mask that indicates what sort of value the field should hold. Values that do not conform to the mask cannot be entered.


mass storage

Refers to various techniques and devices for storing large amounts of data. The earliest storage devices were punched paper cards, which were used as early as 1804 to control silk-weaving looms. Modern mass storage devices include all types of disk drives and tape drives. Mass storage is distinct from memory, which refers to temporary storage areas within the computer. Unlike main memory, mass storage devices retain data even when the computer is turned off.

The main types of mass storage are:

floppy disks: Relatively slow and have a small capacity, but they are portable, inexpensive, and reliable.

hard disks: Very fast and with more capacity than floppy disks, but also more expensive. Some hard disk systems are portable (removable cartridges), but most are not.

optical disks: Unlike floppy and hard disks, which use electromagnetism to encode data, optical disk systems use a laser to read and write data. Optical disks have very large storage capacity, but they are not as fast as hard disks. In addition, the inexpensive optical disk drives are read-only. Read/write varieties are very expensive.

tapes: Relatively inexpensive and can have very large storage capacities, but they do not permit random access of data.

Mass storage is measured in kilobytes (1,024 bytes), megabytes (1,024 kilobytes), and gigabytes (1,024 megabytes).


master/slave

Refers to an architecture in which one device (the master) controls one or more other devices (the slaves).


math coprocessor

See under coprocessor.


mathematical expression

Any expression that represents a numeric value.


matrix

(1) A two-dimensional array; that is, an array of rows and columns.

(2) The background area of color display.


maximize

In graphical user interfaces, to enlarge a window to its maximum size. In Windows 3.x and Macintosh environments, the buttons for minimizing and maximizing windows are located in the top right corner of the window.


MB

Short for megabyte (1,048,576 bytes).


Mbone

Short for Multicast Backbone on the Internet, MBone is an extension to the Internet to support multicasting—two-way transmission of data between multiple sites. The TCP/IP protocol used by the Internet divides messages into packets and sends each packet independently. Packets can travel different routes to their destination which means that they can arrive in any order and with sizable delays between the first and last packets. This works fine for static information, such as text and graphics, but it doesn't work for real-time audio and video.

The MBone is an experiment to upgrade the Internet to handle live multimedia messages.  MBone servers have special Class D IP addresses. Currently, there are only a few thousand such servers on the Internet.

The Mbone was developed by Steve Deering at Xerox PARC and adopted by the Internet Engineering Task Force (IETF) in March 1992 .


Mbyte

Short for megabyte.


MCA

See Micro Channel architecture.


MCGA

Abbreviation of multicolor/graphics array (or memory controller gate array), the graphics system built into some older PCs. It provides graphics capabilities equal to or greater than MDA and CGA, but it is not as powerful as EGA or VGA. Like VGA, MCGA uses analog signals.


MDA

Abbreviation of monochrome display adapter, an old monochrome video standard for PCs. MDA supports high-resolution monochrome text but does not support graphics or colors. The resolution for text is 720 by 350 pixels.


mean time between failures

See MTBF.


media

(1) Objects on which data can be stored. These include hard disks, floppy disks, CD-ROMs, and tapes.

(2) In computer networks, media refers to the cables linking workstations together. There are many different types of transmission media, the most popular being twisted-pair wire (normal electrical wire), coaxial cable (the type of cable used for cable television), and fiber optic cable (cables made out of glass).

(3) The form and technology used to communicate information. Multimedia presentations, for example, combine sound, pictures, and videos, all of which are different types of media.


meg

Short for megabyte.


mega

In decimal systems, the prefix mega means one million, but in binary  systems, mega stands for 2 to the 20th power, or 1,048,576. One megabyte, therefore, is 1,048,576 bytes (this is equivalent to 1,024K).


megabyte

1,048,576 (220) bytes. Megabyte is frequently abbreviated as M or MB.


megaflop

See MFLOP.


megahertz

See MHz.


membrane keyboard

A type of keyboard in which the keys are covered by a transparent, plastic shell. The keys have very little movement, but are sensitive to pressure applied on them. The advantage of membrane keyboards is that the covering protects the components from dirt, but it is difficult to type accurately and quickly.


memory

Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk.

Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information.

There are several different types of memory:

RAM (random-access memory): This is the same as main memory. When used by itself, the term RAM refers to read and write memory; that is, you can both write data into RAM and read data from RAM. This is in contrast to ROM, which permits you only to read data. Most RAM is volatile, which means that it requires a steady flow of electricity to maintain its contents. As soon as the power is turned off, whatever data was in RAM is lost.

ROM (read-only memory): Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to.

PROM (programmable read-only memory): A PROM is a memory chip on which you can store a program. But once the PROM has been used, you cannot wipe it clean and use it to store something else. Like ROMs, PROMs are non-volatile.

EPROM (erasable programmable read-only memory): An EPROM is a special type of PROM that can be erased by exposing it to ultraviolet light.

EEPROM (electrically erasable programmable read-only memory): An EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge.


memory cache

See under cache.


memory controller gate array

See MCGA.


memory dump

See under dump.


memory effect

The property of nickel-cadmium (NiCad) batteries that causes them to lose their capacity for full recharging if they are recharged before they are fully drained. The term derives from the fact that the battery appears to have a memory for the amount of charging it can sustain. If it is recharged when it is already full, it will sustain only a small charge the next time as well, even if it is fully drained. Modern NiCad batteries do not suffer from memory effects as much as older ones do.


memory resident

Permanently in memory. Normally, a computer does not have enough memory to hold all the programs you use. When you want to run a program, therefore, the operating system is obliged to free some memory by copying data or programs from main memory to a disk. This process is known as swapping.

Certain programs, however, can be marked as being memory resident, which means that the operating system is not permitted to swap them out to a storage device; they will always remain in memory.

The programs and data used most frequently are the ones that should be memory resident. This includes central portions of the operating system and special programs, such as calendars and calculators, that you want to be able to access immediately.

Another term for memory resident is RAM resident. In DOS systems, memory-resident programs are called pop-up utilities or TSRs (terminate and stay resident).


menu

A list of commands or options from which you can choose. Most applications now have a menu-driven component. You can choose an item from the menu by highlighting it and then pressing the Enter or Return key, or by simply pointing to the item with a mouse and clicking one of the mouse buttons.

The antithesis of a menu-driven program is a command-driven system, in which you must explicitly enter the command you want rather than choose from a list of possible commands. Menu-driven systems are simpler and easier to learn but are generally not as flexible as command-driven systems, which lend themselves more naturally to interaction with programs.

There are several different types of menus:

pop-up menu: A menu that appears temporarily when you click the mouse button on a selection. Once you make a selection from a pop-up menu, the menu usually disappears.

cascading menu: A submenu that opens when you select a choice from another menu.

pull-down menu: A special type of pop-up menu that appears directly beneath the command you selected.

moving-bar menu: A menu in which options are highlighted by a bar that you can move from one item to another. Most menus are moving-bar menus.

menu bar: A menu arranged horizontally. Each menu option is generally associated with another pull-down menu that appears when you make a selection.

tear-off menu: A pop-up menu that you can move around the screen like a window.


menu bar

A horizontal menu that appears on top of a window. Usually, each option in a menu bar is associated with a pull-down menu.


menu driven

Refers to programs whose user interface employs menus. The antithesis of a menu-driven program is a command-driven program.


merge

(1) To combine two files in such a way that the resulting file has the same organization as the two individual files. For example, if two files contain a list of names in alphabetical order, merging the two files results in one large file with all the names still in alphabetical order.

Note that merge is different from append. Append means to combine two files by adding one of them to the end of the other.

(2) In word processing, mail merge refers to generating form letters by combining one file containing a list of names, addresses, and other information with a second file containing the text of the letter.


message box

Same as alert box.


Messaging Application Programming Interface

See MAPI.


MFLOP

Short for mega floating-point operations per second, MFLOPs are a common measure of the speed of computers used to perform floating-point calculations. Another common measure of computer speed and power is MIPS (million instructions per second), which indicates integer performance.


MFM

Abbreviation of modified frequency modulation, an encoding scheme used by some PC disk drives. A competing scheme, known as RLL (run length limited), produces faster data access speeds and can increase a disk's storage capacity by up to 50 percent.

Technically, any disk drive can use MFM or RLL. The one it uses depends on the disk controller.


MHz

Abbreviation for megahertz. One MHz represents one million cycles per second. The speed of microprocessors, called the clock speed, is measured in megahertz. For example, a microprocessor that runs at 66MHz executes 66 million cycles per second. Each computer instruction requires a fixed number of cycles, so the clock speed determines how many instructions per second the microprocessor can execute. To a large degree, this controls how powerful the microprocessor is. Another chief factor in determining a microprocessor's power is its data width (that is, how many bits it can manipulate at one time).

In addition to microprocessors, the speeds of buses are also measured in MHz.


micro

(1) Short for microprocessor.

(2) Short for personal computer.

(3) A prefix meaning one millionth. For example, a microsecond is one millionth of a second.

(4) Something very small. For example, a microfloppy is a small floppy disk.


Micro Channel Architecture (MCA)

A bus architecture for older PCs. It is called a bus architecture because it defines how peripheral devices and internal components communicate across the computer's expansion bus. Introduced by IBM in 1987, MCA was designed to take the place of the older AT bus, the architecture used on IBM PC-ATs and compatibles. For a variety of reasons, however, the industry never accepted the new architecture.


micro-justification

Refers to the use of microspacing to justify text.


Microcom Networking Protocol

See MNP.


microcomputer

Same as personal computer.


microfloppy disk

A small floppy disk. Microfloppy disks come enclosed in hard, 3½ square-inch casings. Although smaller than older-style floppies, microfloppies have greater storage capacity.

PCs support two types of microfloppies:

•	double-density microfloppies hold 720K.

•	high-density microfloppies can store 1.44MB (megabytes).

For Macintosh computers, which have always used microfloppies, there are three sizes:

•	Single-sided standard microfloppies hold 400K.

•	Double-sided standard microfloppies hold 800 K.

•	Double-sided, high-density microfloppies hold 1.44 megabytes.


microprocessor

A silicon chip that contains a CPU. In the world of personal computers, the terms microprocessor and CPU are used interchangeably. At the heart of all personal computers and most workstations sits a microprocessor. Microprocessors also control the logic of almost all digital devices, from clock radios to fuel-injection systems for automobiles.

Two basic characteristics differentiate microprocessors:

bandwidth: The number of bits processed in a single instruction.

clock speed: Given in megahertz (MHz), the clock speed determines how many instructions per second the processor can execute.

In both cases, the higher the value, the more powerful the CPU. For example, a 32-bit microprocessor that runs at 50MHz is more powerful than a 16-bit microprocessor that runs at 25MHz.

In addition to bandwidth and clock speed, microprocessors are classified as being either RISC (reduced instruction set computer) or CISC (complex instruction set computer).


Microsoft Windows

A family of operating systems for personal computers. Windows dominates the personal computer world, running, by some estimates, on 90% of all personal computers. The remaining 10% are mostly Macintosh computers. Like the Macintosh operating environment, Windows provides a graphical user interface (GUI), virtual memory management, multitasking, and support for many peripheral devices.

In addition to Windows 3.x and Windows 95, which run on Intel-based machines, Microsoft also sells Windows NT, a more advanced operating system that runs on a variety of hardware platforms.


microspacing

The insertion of variable-sized spaces between letters to justify text. For example, the following justified text uses microspacing:

This text is right- and left-justified and is microspaced. Compare with the following example, which is not microspaced.

Without microspacing, the text would look like the following:

This text is right- and left-justified and is “not” microspaced. Compare with the previous example, which is microspaced.

Some word processors are capable of microspacing. To print microspaced text, however, you need an ink-jet or laser printer. Most daisy-wheel printers and inexpensive dot-matrix printers are not capable of microspacing.


MIDI

Pronounced middy, an acronym for musical instrument digital interface, a standard adopted by the electronic music industry for representing and transmitting sounds in a form that electronic devices can use. At minimum, a MIDI representation of a sound includes values for the note's pitch, length, and volume. It can also include additional characteristics, such as attack and delay time.

The MIDI standard is supported by most synthesizers, so sounds created on one synthesizer can be played and manipulated on another synthesizer. Computers that have a MIDI interface can record sounds created by a synthesizer and then manipulate the data to produce new sounds. For example, you can change the key of a composition with a single keystroke.

A number of software programs are available for composing and editing music that conforms to the MIDI standard. They offer a variety of functions: for instance, when you play a tune on a keyboard connected to a computer, a music program can translate what you play into a written score.


million instructions per second

See MIPS.


millisecond

One thousandth of a second. Access times of hard disk drives are measured in milliseconds, usually abbreviated as ms .


MIME

Short for Multipurpose Internet Mail Extensions, a specification for formatting non-ASCII messages so that they can be sent over the Internet. Many e-mail clients now support MIME, which enables them to send and receive graphics, audio, and video files via the Internet mail system. In addition, MIME supports messages in character sets other than ASCII.

There are many predefined MIME types, such as GIF graphics files and PostScript files. It is also possible to define your own MIME types.

In addition to e-mail applications, Web browsers also support various MIME types. This enables the browser to display or output files that are not in HTML format.

MIME was defined in 1992 by the Internet Engineering Task Force (IETF).


mini

Short for minicomputer.


minicomputer

A midsized computer. In size and power, minicomputers lie between workstations and mainframes. In the past decade, the distinction between large minicomputers and small mainframes has blurred, however, as has the distinction between small minicomputers and workstations. But in general, a minicomputer is a multiprocessing system capable of supporting from 4 to about 200 users simultaneously.

The most popular model of minicomputer is the VAX made by Digital Equipment Corporation. Other large manufacturers of minicomputers include IBM, Data General, and Prime Computer.


minifloppy

A 5¼-inch floppy disk.


minimize

In graphical user interfaces, to convert a window into an icon.


minitower

See under tower model.


MIPS

Acronym for million instructions per second. A common measure of a computer's speed and power, MIPS measures roughly the number of machine instructions that a computer can execute in one second. However, different instructions require more or less time than others, and there is no standard method for measuring MIPS. In addition, MIPS refers only to the CPU speed, whereas real applications are generally limited by other factors, such as I/O speed. A machine with a high MIPS rating, therefore, might not run a particular application any faster than a machine with a low MIPS rating.

Despite these problems, the MIPS rating can give you a general idea of a computer's speed. The IBM PC/XT computer, for example, is rated at ¼ MIPS, while Pentium-based PCs run at over 100 MIPS.


MIS

Short for management information system, MIS refers to a class of software that provides managers with tools for organizing and evaluating their department. Typically, MIS systems are written in COBOL and run on mainframes or minicomputers.


MNP

Abbreviation of Microcom Networking Protocol, a communications protocol developed by Microcom, Inc., that is used by many high-speed modems. MNP supports several different classes of communication, each higher class providing additional features. Modems can support one or more classes. Class 4 provides error detection and automatically varies the transmission speed based on the quality of the line. Class 5 provides data compression. Class 6 attempts to detect the highest transmission speed of the modem at the other end of the connect and transmit at that speed.

The most common levels of MNP support are Class 4 and Class 5, frequently called MNP-4 and MNP-5. Using the data compression techniques provided by MNP-5, devices can double normal transmission speeds.

Because MNP is built into the modem hardware, it affects all data transmission. In contrast, software protocols, such as Xmodem and Kermit, affect only file transfer operations.


MO drive

See magneto-optical (MO) drive.


mode

The state or setting of a program or device. For example, when a word processor is in insert mode, characters that you type are inserted at the cursor position. In overstrike mode, characters typed replace existing characters.

The term mode implies a choice—that you can change the setting and put the system in a different mode.


modem

Acronym for modulator-demodulator. A modem is a device that enables a computer to transmit data over telephone lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms. (Note that ISDN telephone lines send data digitally, so they do not require modems.)

Fortunately, there is one standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have. There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems and are more machine specific.

While the modem interfaces are standardized, a number of different protocols for formatting data to be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, while others have been developed by private companies. Most modems have built-in support for the more common protocols—at slow data transmission speeds at least, most modems can communicate with each other. At high transmission speeds, however, the protocols are less standardized.

Aside from the transmission protocols that they support, the following characteristics distinguish one modem from another:

bps: How fast the modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 28,800 bps, although they can achieve even higher data transfer rates by compressing the data. Obviously, the faster the transmission rate, the faster you can send and receive data. Note, however, that you cannot receive data any faster than it is being sent. If, for example, the device sending data to your computer is sending it at 2,400 bps, you must receive it at 2,400 bps. It does not always pay, therefore, to have a very fast modem. In addition, some telephone lines are unable to transmit data reliably at very high rates.

voice/data: Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication.

auto-answer: An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use.

data compression: Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique.

flash memory: Some modems come with flash memory rather than conventional ROM, which means that the communications protocols can be easily updated if necessary.

To get the most out of a modem, you should have a communications software package, a program that simplifies the task of transferring data.


modified frequency modulation

See MFM.


modifier key

A key on a keyboard that only has a meaning when combined with another key. Examples of modifier keys include the Shift, Control, and Alt keys.


Modula-2

A programming language designed by Niklaus Wirth, the author of Pascal. Wirth created Modula-2 in the late 1970s to answer many of the criticisms leveled at Pascal, which he had created ten years earlier. In particular, Modula-2 addresses Pascal's lack of support for separate compilation of modules and multitasking. Although Modula-2 found support in academia, it is not often used for applications.


modular architecture

Refers to the design of any system composed of separate components that can be connected together. The beauty of modular architecture is that you can replace or add any one component (module) without affecting the rest of the system. The opposite of a modular architecture is an integrated architecture, in which no clear divisions exist between components.

The term modular can apply to both hardware and software. Modular software design, for example, refers to a design strategy in which a system is composed of relatively small and autonomous routines that fit together.


module

(1) In software, a module is a part of a program. Programs are composed of one or more independently developed modules that are not combined until the program is linked. A single module can contain one or several routines.

(2) In hardware, a module is a self-contained component.


moiré

An undesirable pattern that appears when a graphic image is displayed or printed with an inappropriate resolution. Moiré patterns are difficult to predict because they result from a complex combination of parameters: the size of the image, resolution of the image, resolution of the output device, halftone screen angle, etc.

If you’re planning to print a graphic image (particularly a bit-mapped image) on a high-resolution printer, it’s a good idea to print  a test page first to see if there are any moiré patterns. If there are, you can sometimes eliminate them by changing the resolution of the printout, resizing the image, or changing the angle of the halftone screen.


monitor

(1) Another term for display screen. The term monitor, however, usually refers to the entire box, whereas display screen can mean just the screen. In addition, the term monitor often implies graphics capabilities.

There are many ways to classify monitors. The most basic is in terms of color capabilities, which separates monitors into three classes:

monochrome: Monochrome monitors actually display two colors, one for the background and one for the foreground. The colors can be black and white, green and black, or amber and black.

gray-scale: A gray-scale monitor is a special type of monochrome monitor capable of displaying different shades of gray.

color: Color monitors can display anywhere from 16 to over 1 million different colors. Color monitors are sometimes called RGB monitors because they accept three separate signals—red, green, and blue.

Color and gray-scaling monitors are often classified by the number of bits they use to represent each pixel. For example, an 8-bit monitor represents each pixel with 8 bits. The more bits per pixel, the more colors and shades of gray the monitor can display.

After this classification, the most important aspect of a monitor is its screen size. Like televisions, screen sizes are measured in diagonal inches, the distance from one corner to the opposite corner diagonally. A typical size for small VGA monitors is 14 inches. Monitors that are 16 or more inches diagonally are often called full-page monitors. In addition to their size, monitors can be either portrait (height greater than width) or landscape (width greater than height). Larger landscape monitors can display two full pages, side by side. The screen size is sometimes misleading because there is always an area around the edge of the screen that can't be used. Therefore, monitor manufacturers must now also state the viewable areathat is, the area of screen that is actually used.

The resolution of a monitor indicates how densely packed the pixels are. In general, the more pixels (often expressed in dots per inch), the sharper the image. Most modern monitors can display 1024 by 768 pixels, the SVGA standard. Some high-end models can display 1280 by 1024, or even 1600 by 1200.

Another common way of classifying monitors is in terms of the type of signal they accept: analog or digital. Low-cost digital monitors are often called TTL monitors. Most monitors accept analog signals, which is required by the VGA, SVGA, 8514/A, and other high-resolution color standards. Some monitors are capable of accepting either type of signal.

Some monitors are fixed frequency, which means that they accept input at only one frequency. Another type of monitor, called a multiscanning monitor, automatically adjusts to the frequency of the signals being sent to it. This means that it can accept input from different types of video adapters. Like fixed-frequency monitors, multiscanning monitors accept TTL, analog, or both types of input.

Other factors that determine a monitor's quality include the following:

bandwidth: The range of signal frequencies the monitor can handle. This determines how much data it can process.

refresh rate: How many times per second the screen is refreshed (redrawn). To avoid flickering, the refresh rate should be at least 70 Hz.

interlaced or noninterlaced: Interlacing is a technique that enables a monitor to have more resolution, but it reduces the monitor's reaction speed.

dot pitch: The amount of space between each pixel. The smaller the dot pitch, the sharper the image. However, very small dot pitches may also translate into decreased brightness and contrast.

convergence: The clarity and sharpness of each pixel.

(2) A program that observes a computer. For example, some monitor programs report how often another program accesses a disk drive or how much CPU time it uses.


monochrome

One color. Monitors, for example, can be monochrome, grayscale or color. Monochrome monitors actually use two colors, one for the display image (the foreground) and one for the background. Graphic images can also be monochrome, grayscale, or color.


monochrome display adapter

See MDA.


monospacing

Refers to fonts in which each character has the same width. The opposite of monospacing is proportional spacing, in which different characters have different widths. For example, in a proportionally spaced font, the letter o would be wider than the letter i. Proportionally spaced fonts look more professional, but monospaced fonts are often superior for tabular data because the uniform width of each character makes alignment of columns easier.

Most printed matter, including this book, uses proportional spacing.


morphing

Short for metamorphosing, morphing refers to an animation technique in which one image is gradually turned into another. Many advanced animation programs support some type of morphing feature.


Mosaic

An application that simplifies accessing documents on the World Wide Web. Originally produced by the National Center for Supercomputing Applications (NCSA), Mosaic has always been distributed as freeware. In 1994, however, the NCSA turned over commercial development of the program to a company called Spyglass. There are now several varieties of Mosaic, some free and some for sale.


motherboard

The main circuit board of a microcomputer. The motherboard contains the connectors for attaching additional boards. Typically, the motherboard contains the CPU, BIOS, memory, mass storage interfaces, serial and parallel ports, expansion slots, and all the controllers required to control standard peripheral devices, such as the display screen, keyboard, and disk drive. Other circuit boards are called add-ons or expansion boards.

Because the motherboard contains the CPU, all other chips attached to the motherboard can access the CPU directly without going through the bus. For this reason, it is a good idea to fill up the motherboard completely before adding expansion boards. For example, to add memory to your system, you may be able to insert chips directly onto the motherboard instead of purchasing a separate memory board.

On most PCs, it is possible to replace the motherboard to upgrade to a faster microprocessor. Replacing the motherboard is somewhat more difficult and more expensive than adding an accelerator board, but it has two advantages:

•	The motherboard contains the bus, ROM, and main memory. Replacing it, therefore, improves performance of all of these components in addition to adding a faster CPU. Also, by replacing everything at once, you can avoid potential compatibility problems.

•	Replacing the motherboard avoids using up one of the expansion slots.


Motion Picture Experts Group

See MPEG.


motion-JPEG

JPEG stands for the Joint Photographic Experts Group standard, a standard for storing and compressing digital images. Motion-JPEG extends this standard by supporting videos. In motion-JPEG, each frame in the video is stored with the JPEG format.


Motorola microprocessors

Motorola Inc. is one of the leading manufacturers of microprocessors. Until the early 1990s, Motorola microprocessors were used in all Apple Macintosh computers and in many workstations. Following the development of its 68040 chip in 1989, however, Motorola abandoned the 680x0 line of CISC chips in favor of RISC technologies. In 1993, Motorola joined Apple Computer and IBM in designing a new RISC architecture that would form the basis of the next generation of personal computers. This effort culminated in the introduction of the PowerPC architecture in 1994.

There are four main chips in the 680x0 family: the 6800, 68020, 68030, and 68040. Many people refer to them by their last three digits. For example, the “oh-forty” refers to the 68040 chip.


mount

(1) To make a mass storage device available. In Macintosh environments, for example, inserting a floppy disk into the drive is called mounting the floppy.

(2) To install a device, such as a disk drive or expansion board.


mouse

A device that controls the movement of the cursor or pointer on a display screen. A mouse is a small object you can roll along a hard, flat surface. Its name is derived from its shape, which looks a bit like a mouse, its connecting wire that one can imagine to be the mouse's tail, and the fact that one must make it scurry along a surface. As you move the mouse, the pointer on the display screen moves in the same direction. Mice contain at least one button and sometimes as many as three, which have different functions depending on what program is running.

Invented by Douglas Engelbart of Stanford Research Center in 1963, and pioneered by Xerox in the 1970s, the mouse is one of the great breakthroughs in computer ergonomics because it frees the user to a large extent from using the keyboard. In particular, the mouse is important for graphical user interfaces because you can simply point to options and objects and click a mouse button. Such applications are often called point-and-click programs. The mouse is also useful for graphics programs that allow you to draw pictures by using the mouse like a pen, pencil, or paintbrush.

There are three basic types of mice:

mechanical: Has a rubber or metal ball on its underside that can roll in all directions. Sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.

optical: Uses a laser to detect the mouse's movement. You must roll the mouse along a special mat with a grid so that the optical mechanism has a frame of reference. Optical mice respond more quickly and precisely than mechanical mice, but they are also more expensive.

optomechanical: Uses a combination of the mechanical and optical technologies. Unlike optical mice, however, optomechanical mice do not require gridded mats.

Mice connect to PCs in one of three ways:

Serial mice connect directly to an RS-232C serial port. This is the simplest type of connection.

Bus mice connect to the bus through an interface card. This is somewhat more complicated because you need to configure and install an expansion board.

Cordless mice aren’t physically connected at all. Instead they rely on infrared or radio waves to communicate with the computer.

The choice between the first two connections depends on whether you have a free serial port. If you do, it is usually simpler to connect a serial mouse. Cordless mice are more expensive than both serial and bus mice, but they do eliminate the cord, which can sometimes get in the way.

Mice connect to Macintosh computers through the ADB (Apple Desktop bus) port.


mouse pointer

See under pointer.


mousepad

A pad over which you can move a mouse. Mousepads provide more traction than smooth surfaces such as glass and wood, so they make it easier to move a mouse accurately.

For mechanical mice, mousepads are optional. Optical mice, however, require special mousepads that have grids drawn on them.


moving-bar menu

A common type of menu in which options are selected by moving a highlighted bar over them. You can move the bar with a mouse or with arrow keys, or sometimes with the Tab key.


MPC

Abbreviation of Multimedia Personal Computer, a software and hardware standard developed by a consortium of computer firms led by Microsoft. There are two MPC standards, called MPC and MPC-2, respectively. Each specifies a minimum hardware configuration for running multimedia software. To run MPC-2 software, you need at least an Intel 486SX microprocessor with a clock speed of 25MHz, 8MB (megabytes) of RAM, a VGA display, and a double-speed CD-ROM drive.


MPEG

Short for Motion Picture Experts Group, one of the leading standards for compressing full-motion digital video. Unlike some competing standards, such as Video for Windows, Indeo and QuickTime, MPEG requires special hardware for decompression. However, it produces better results than these software-only solutions.

The MPEG-1 standard defines a video resolution of 352-by-240 at 30 frames per second (fps). This produces video quality slightly below the quality of conventional VCR videos.


ms

Short for millisecond, one thousandth of a second. Access times of mass storage devices are often measured in milliseconds.


MS-DOS

Pronounced em-ess-doss. See under DOS.


MS-Windows

Pronounced emm-ess-windows. See Microsoft Windows.


MTBF

Short for mean time between failures. MTBF ratings are measured in hours and indicate the sturdiness of hard disk drives and printers.

Typical disk drives for personal computers have MTBF ratings of about 40,000 hours. This means that at least half of the disk drives with such a rating will fail once in the first 40,000 hours of operation. Most working conditions are not ideal, so MTBF ratings can be considered as only approximate guidelines for judging the hardiness of disk drives. The fact that MTBF ratings exist at all, however, underscores the fact that every disk drive will eventually fail if run long enough.


multi-user

Refers to computer systems that support two or more simultaneous users. All mainframes and minicomputers are multi-user systems, but most personal computers and workstations are not. Another term for multi-user is time sharing.


Multicast Backbone (MBone)

See MBone.


multicolor/graphics array

See MCGA.


MultiFinder

The multitasking version of Finder for Apple Macintosh computers. This is the part of the operating system responsible for managing the desktop—locating documents and folders and handling the Clipboard and Scrapbook. For System 6, and earlier versions of the Macintosh operating system, MultiFinder was optional. Since System 7, MultiFinder has replaced the older Finder.


multifrequency monitor

A type of video monitor capable of accepting signals at more than one frequency range. This enables the monitor to support several different video standards. Typically, multifrequency monitors for PCs support MDA, Hercules, CGA, VGA, and sometimes SVGA.

Multifrequency monitors differ somewhat from multiscanning monitors. Multiscanning monitors can support video signals at any frequency level within its range, whereas multifrequency monitors support only a select number of frequency levels. However, because almost all video signals conform to one of a handful of video standards, the greater potential of multiscanning monitors is generally not utilized.


multimedia

The use of computers to present text, graphics, video, animation, and sound in an integrated way. Long touted as the future revolution in computing, multimedia applications were, until the mid-90s, uncommon due to the expensive hardware required. With recent increases in performance and decreases in price, however, multimedia is finally finding its way into the mainstream of personal computer applications. To date, most multimedia titles have been games or reference works, but we can expect other types of applications to use multimedia in the future.

Because of the storage demands of multimedia applications, the most effective media are CD-ROMs.


multimedia kit

A package of hardware and software that adds multimedia capabilities to a computer. Typically a multimedia kit includes a CD-ROM player, a sound card, speakers, and a bundle of CD-ROMs.


Multimedia Personal Computer

See MPC.


multiprocessing

(1) Refers to a computer system's ability to support more than one process (program) at the same time. Multiprocessing operating systems enable several programs to run concurrently. UNIX is one of the most widely used multiprocessing systems, but there are many others, including OS/2 for high-end PCs. Multiprocessing systems are much more complicated than single-process systems because the operating system must allocate resources to competing processes in a reasonable manner.

(2) Refers to the utilization of multiple CPUs in a single computer system. This is also called parallel processing.


Multipurpose Internet Mail Extensions (MIME)

See MIME.


multiscanning monitor

A type of monitor that automatically adjusts to the signal frequency of the video display board to which it is connected. Consequently, multiscanning monitors can display images based on almost any graphics display system, including MDA, Hercules, EGA, VGA, and SVGA.

In contrast, fixed-frequency monitors respond to only one, or a few, frequencies, so they can connect to a limited number of video display boards. However, fixed-frequency monitors are less expensive than multiscanning monitors and sometimes produce sharper images.

Multiscanning monitors are also called multisync, multifrequency, and variable-frequency monitors. Increasingly, however, the term multifrequency monitor is reserved for monitors that support a fixed number of video frequencies. In contrast, multiscanning monitors scan the incoming signals and set themselves to whatever frequency range they are receiving. In practice, there is little difference between the two types of monitors because most video signals conform to one of a handful of video standards.


multisync monitor

Same as multiscanning monitor.


multitasking

The ability to execute more than one task at the same time, a task being a program. The terms multitasking and multiprocessing are often used interchangeably, although multiprocessing sometimes implies that more than one CPU is involved.

In multitasking, only one CPU is involved, but it switches from one program to another so quickly that it gives the appearance of executing all of the programs at the same time.

There are two basic types of multitasking: preemptive and cooperative. In preemptive multitasking, the operating system parcels out CPU time slices to each program. In cooperative multitasking, each program can control the CPU for as long as it needs it. If a program is not using the CPU, however, it can allow another program to use it temporarily. OS/2 and UNIX use preemptive multitasking, whereas Microsoft Windows and the MultiFinder (for Macintosh computers) use cooperative multitasking.


multithreading

The ability of an operating system to execute different parts of a program, called threads, simultaneously. The programmer must carefully design the program in such a way that all the threads can run at the same time without interfering with each other.


musical instrument digital interface

See MIDI.


name

A sequence of one or more characters that uniquely identifies a file, variable, account, or other entity. Computer systems impose various rules about naming objects. For example, there is often a limit to the number of characters you can use, and not all characters are allowed.

Names are sometimes called identifiers.


nanosecond

A billionth of a second. Many computer operations, such as the speed of memory chips, are measured in nanoseconds. Nanosecond is often abbreviated as ns.


National Television Standards Committee

See NTSC.


native

Referring to an original form. For example, many applications can work with files in a variety of formats, but an application’s native file format is the one it uses internally. For all other formats, the application must first convert the file to its native format.


natural language

A human language. For example, English, French, and Chinese are natural languages. Computer languages, such as FORTRAN and C, are not.

Probably the single most challenging problem in computer science is to develop computers that can understand natural languages. So far, the complete solution to this problem has proved elusive, although a great deal of progress has been made. Fourth-generation languages are the programming languages closest to natural languages.


navigation keys

Same as cursor control keys.


near letter quality

A quality of print that is not quite letter quality, but is better than draft quality. Many dot-matrix printers produce near letter quality print.

Near letter quality is often abbreviated NLQ.


nesting

Embedding one object in another object of the same type. Nesting is quite common in programming. It also occurs in applications. For example, many word processing applications allow you to embed (nest) one document inside another.


Net

Short for Internet, as in “I found this on file on the Net.”


NetBIOS

Short for Network Basic Input Output System, an application programming interface (API) that augments the DOS BIOS by adding special functions for local-area networks (LANs). Almost all LANs for PCs are based on the NetBIOS. Some LAN manufacturers have even extended it, adding additional network capabilities.


netiquette

The etiquette guidelines for posting messages to online services, and particularly Internet newsgroups. Netiquette covers not only rules to maintain civility in discussions (i.e., avoiding flames), but also special guidelines unique to the electronic nature of forum messages. For example, netiquette advises users to use simple formats because complex formatting may not appear correctly for all readers. In most cases, netiquette is enforced by fellow users who will vociferously object if you break a rule of netiquette.


NetWare

A popular local-area network (LAN) operating system developed by Novell Corporation. NetWare is a software product that runs on a variety of different types of LANs, from Ethernets to IBM token-ring networks. It provides users and programmers with a consistent interface that is independent of the actual hardware used to transmit messages.


network

A group of two or more computer systems linked together. There are many types of computer networks, including:

local-area networks (LANs): The computers are geographically close together (that is, in the same building).

wide-area networks (WANs): The computers are farther apart and are connected by telephone lines or radio waves.

In addition to these types, the following characteristics are also used to categorize different types of networks:

topology: The geometric arrangement of a computer system. Common topologies include a bus, star, and ring.

protocol: The protocol defines a common set of rules and signals that computers on the network use to communicate. One of the most popular protocols for LANs is called Ethernet. Another popular LAN protocol for PCs is the IBM token-ring network.

architecture: Networks can be broadly classified as using either a peer-to-peer or client/server architecture.

Computers on a network are sometimes called nodes. Computers and devices that allocate resources for a network are called servers.


Network Basic Input/Output System

See NetBIOS.


network interface card (NIC)

A expansion board you insert into a computer so the computer can be connected to a network. Most NICs are designed for a particular type of network, protocol, and media, although some can serve multiple networks.


network operating system (NOS)

An operating system that includes special functions for connecting computers and devices into a local-area network (LAN). Some operating systems, such as UNIX and the Mac OS, have networking functions built in. The term network operating system, however, is generally reserved for software that enhances a basic operating system by adding networking features. For example, some popular NOS’s for DOS and Windows systems include Novell Netware, Artisoft’s LANtastic, and Microsoft LAN Manager.


neural network

A type of artificial intelligence that attempts to imitate the way a human brain works. Rather than using a digital model, in which all computations manipulate zeros and ones, a neural network works by creating connections between processing elements, the computer equivalent of neurons. The organization and weights of the connections determine the output.

Neural networks are particularly effective for predicting events when the networks have a large database of prior examples to draw on. Strictly speaking, a neural network implies a non-digital computer, but neural networks can be simulated on digital computers.

The field of neural networks was pioneered by Bernard Widrow of Stanford University in the 1950s. To date, there are very few commercial applications of neural networks, but the approach is beginning to prove useful in certain areas that involve recognizing complex patterns, such as voice recognition.


newbie

Slang term for someone who is a new user on an online service, particularly the Internet.


newsgroup

Same as forum.


NextStep

An object-oriented operating system developed by Next Inc., a company started in 1985 by Steven Jobs, one of the co-founders of Apple Computer. Although NextStep is considered by many experts to be a technical masterpiece, it has failed to gain significant market share.


NIC

See network interface card.


NiCad battery pack

NiCad stands for nickel-cadmium, the materials used in the battery packs for many notebook computers. NiCad batteries can provide considerable power, but they need to be recharged every three or four hours. Full recharging can take as much as twelve hours, although newer batteries can be recharged in just a few hours.

Older NiCad batteries suffer from a phenomenon known as the memory effect. If they were only partially drained and then recharged, they lost their capacity to be fully charged. This is not such a problem with modern NiCad batteries.

Even with full drainage (called deep discharging), all batteries have a limit to the number of times they can be recharged. The maximum for most NiCad batteries is about one thousand recharges.


NiMH battery pack

NiMH stands for Nickel-Metal Hydride, the materials used in some battery packs. Unlike the more common NiCad batteries, NiMH batteries use heavy metals that may have toxic effects. However, they can store up to 50% more power than NiCad batteries and do not suffer from memory effects.


NLQ

Stands for near letter quality.


node

(1) In networks, a processing location. A node can be a computer or some other device, such as a printer.

(2) In tree structures, a node is a point where two or more lines meet.


noise

In communications, interference (static) that destroys the integrity of signals on a line. Noise can come from a variety of sources, including radio waves, nearby electrical wires, lightning, and bad connections. One of the major advantages of fiber optic cables over metal cables is that they are much less susceptible to noise.


non-impact printer

A type of printer that does not operate by striking a head against a ribbon. Examples of nonimpact printers include laser and ink-jet printers. The term nonimpact is important primarily in that it distinguishes quiet printers from noisy (impact) printers.


non-interlaced

Refers to monitors and video standards that do not use interlacing techniques to improve resolution. Although interlacing increases resolution, it also increases screen flicker and reduces reaction time.


non-volatile memory

Types of memory that retain their contents when power is turned off. ROM is nonvolatile, whereas RAM is volatile.


NOR operator

A Boolean operator that returns a value of TRUE only if both operands are FALSE.


NOS

See network operating system.


NOT operator

A Boolean operator that returns TRUE if its operand is FALSE, and FALSE if its operand is TRUE.


notebook computer

An extremely lightweight personal computer. Notebook computers typically weigh less than 6 pounds and are small enough to fit easily in a briefcase. Aside from size, the principal difference between a notebook computer and a personal computer is the display screen. Notebook computers use a variety of techniques, known as flat-panel technologies, to produce a lightweight and non-bulky display screen.

The quality of notebook display screens varies considerably. In general, notebook display screens are limited to VGA resolution. Active-matrix screens produce very sharp images, but they do not refresh as rapidly as full-size monitors.

In terms of computing power, modern notebook computers are nearly equivalent to personal computers. They have the same CPUs, memory capacity, and disk drives. However, all this power in a small package is expensive. Notebook computers cost about twice as much as equivalent regular-sized computers.

Notebook computers come with battery packs that enable you to run them without plugging them in. However, the batteries need to be recharged every few hours.


Novell NetWare

See under NetWare.


ns

Short for nanosecond.


NSFnet

A wide-area network developed under the auspices of the National Science Foundation (NSF). NSFnet is replacing ARPANET as the main government network linking universities and research facilities.


NTSC

Abbreviation of National Television Standards Committee. The NTSC is responsible for setting television and video standards in the United States (in Europe and the rest of the world, the dominant television standards are PAL and SECAM). The NTSC standard for television defines a composite video signal with a refresh rate of 60 half-frames (interlaced) per second. Each frame can contain 16 million different colors.

The NTSC standard is incompatible with most computer video standards, which generally use RGB video signals. However, you can insert special video adapters into your computer that convert NTSC signals into computer video signals and vice versa.


NuBus

The expansion bus for all versions of the Macintosh computers starting with the Macintosh II. Apple has indicated that sometime in the future it may replace NuBus with PCI.


null character

A character that has all its bits set to 0. A null character, therefore, has a numeric value of 0, but it has a special meaning when interpreted as text. In some programming languages, notably C, a null character is used to mark the end of a character string. In database and spreadsheet applications, null characters are often used as padding and are displayed as spaces.


null-modem cable

A specially designed cable that allows you to connect two computers directly to each other via their communications ports (RS-232 ports). Null modems are particularly useful with portable computers because they enable the portable computer to exchange data with a larger system.


Num Lock key

A key that switches the numeric keypad from numeric mode to cursor control mode, and vice versa. In numeric mode, the keys represent numbers even when they are combined with the Shift key, Function key, or Control key. Otherwise these combinations may have different meanings.

The Num Lock key is a toggle key, meaning that it changes the current mode. If the numeric keypad is already locked in numeric mode, pressing the Num Lock key releases it.


number cruncher

(1) A computer whose dominant characteristic is its ability to perform large amounts of numerical computations quickly. Supercomputers, for example, are sometimes called number crunchers. In addition, the term number cruncher is often applied to powerful workstations.

(2) The term number cruncher is sometimes applied to programs. For example, statistical programs are number crunchers because their main task is to perform mathematical calculations.

(3) Less frequently, the term number cruncher refers to individuals who use a computer primarily for analyzing numbers.


numeric coprocessor

See under coprocessor.


numeric keypad

A separate set of keys on some keyboards that contain the numbers 0 through 9 and a decimal point arranged as on an adding machine. Numeric keypads make it easier to enter large amounts of numeric data.

Frequently, the keys on the numeric keyboard also serve as cursor control keys. Their meanings, therefore, depend on what mode the numeric keypad is in. In numeric mode, they represent numbers; in cursor control mode, they are like arrow keys. Keyboards that support these dual functions contain an additional key that enables you to switch modes. The name of this key varies—on many keyboards it is labeled Num Lock.


OA

Short for office automation.


object

Generally, any item that can be individually selected and manipulated. This can include shapes and pictures that appear on a display screen as well as less tangible software entities. In object-oriented programming, for example, an object is a self-contained entity that consists of both data and procedures to manipulate the data.


object code

The code produced by a compiler. Programmers write programs in a form called source code. The source code consists of instructions in a particular language, like C or FORTRAN. Computers, however, can only execute instructions written in a low-level language called machine language.

To get from source code to machine language, the programs must be transformed by a compiler. The compiler produces an intermediary form called object code. Object code is often the same as or similar to a computer's machine language. The final step in producing an executable program is to transform the object code into machine language, if it is not already in this form. This can be done by a number of different types of programs, called assemblers, binders, linkers, and loaders.


Object Linking and Embedding

See OLE.


object oriented

A popular buzzword that can mean different things depending on how it is being used. Object-oriented programming (OOP) refers to a special type of programming that combines data structures with functions to create re-usable objects (see under object-oriented programming). Object-oriented graphics is the same as vector graphics.

Otherwise, the term object-oriented is generally used to describe a system that deals primarily with different types of objects, and where the actions you can take depend on what type of object you are manipulating. For example an object-oriented draw program might enable you to draw many types of objects, such as circles, rectangles, triangles, etc. Applying the same action to each of these objects, however, would produce different results. If the action is Make 3D, for instance, the result would be a sphere, box, and pyramid, respectively.


object-oriented graphics

The representation of graphical objects, such as lines, arcs, circles, and rectangles, with mathematical formulas. This method of describing objects enables the system to manipulate the objects more freely. In an object-oriented system, for example, you can overlap objects but still access them individually, which is difficult in a bit-mapped system. Also, object-oriented images profit from high-quality output devices. The higher the resolution of a monitor or printer, the sharper an object-oriented image will look. In contrast, bit-mapped images always appear the same regardless of a device's resolution.

One of the most widely used formats for object-oriented graphics is PostScript. PostScript is a page description language (PDL) that makes it possible to describe objects and manipulate them in various ways. For example, you can make objects smaller or larger, turn them at various angles, and change their shading and color. A font described in PostScript, therefore, can easily be transformed into another font by changing its size or weight. Object-oriented fonts are called outline fonts, scalable fonts, or vector fonts.

Object-oriented graphics is also called vector graphics, whereas bit-mapped graphics is sometimes called raster graphics.


object-oriented programming (OOP)

A type of programming in which programmers define not only the data type of a data structure, but also the types of operations (functions) that can be applied to the data structure. In this way, the data structure becomes an object that includes both data and functions. In addition, programmers can create relationships between one object and another. For example, objects can inherit characteristics from other objects.

One of the principal advantages of object-oriented programming techniques over conventional programming techniques is that they enable programmers to create modules that do not need to be changed when a new type of object is added. A programmer can simply create a new object that inherits many of its features from existing objects. This makes object-oriented programs easier to modify.

To perform object-oriented programming, one needs an object-oriented programming language (OOPL). C++ and Smalltalk are two of the more popular languages, and there are also object-oriented versions of Pascal.


OCR

See optical character recognition.


octal

Refers to the base-8 number system, which uses just eight unique symbols (0, 1, 2, 3, 4, 5, 6, and 7). Programs often display data in octal format because it is relatively easy for humans to read and can easily be translated into binary format , which is the most important format for computers. By contrast, decimal format is the easiest format for humans to read because it is the one we use in everyday life, but translating between decimal and binary formats is relatively difficult.

In octal format, each digit represents three binary  digits, as shown:

With this table it is easy to translate between octal and binary . For example, the octal number 3456 is 011 100 101 110 in binary .


ODBC

Abbreviation of Open DataBase Connectivity, a standard database access method developed by Microsoft Corporation. The goal of ODBC is to make it possible to access any data from any application, regardless of which database management system (DBMS) is handling the data. ODBC manages this by inserting a middle layer, called a database driver, between an application and the DBMS. The purpose of this layer is to translate the application’s data queries into commands that the DBMS understands. For this to work, both the application and the DBMS must be ODBC-compliant—that is, the application must be capable of issuing ODBC commands and the DBMS must be capable of responding to them. Since version 2.0, the standard supports SAG SQL.


odd header

In word processing, a header that appears only on odd-numbered pages.


odd parity

The mode of parity checking in which each byte contains an odd number of set bits.


OEM

(n) Stands for original equipment manufacturer, which is a misleading term for a company that has a special relationship with computer producers. OEMs buy computers in bulk and customize them for a particular application. They then sell the customized computer under their own name. The term is really a misnomer because OEMs are not the original manufacturers—they are the customizers.

Another term for OEM is VAR (value-added reseller).

(v) To provide equipment to another company, an OEM, which customizes and markets the equipment.


off-line

(1) Not connected. For example, all printers have a switch that allows you to turn them off-line. While the printer is off-line, you can perform certain commands like advancing the paper (form feed), but you cannot print documents sent from the computer. The opposite of off-line is on-line.

(2) Aside from its technical meaning, off-line is used frequently in a more general sense to describe events that occur outside of a standard procedure. For example, if somebody at a meeting says “let’s continue this discussion off-line,” it means “let’s discuss it informally at another time.”


office automation

The use of computer systems to execute a variety of office operations, such as word processing, accounting, and e-mail. Office automation almost always implies a network of computers with a variety of available programs.


offset

(1) Refers to a value added to a base address to produce a second address. For example, if B represents address 100, then the expression,

B+5

would signify the address 105. The 5 in the expression is the offset.

Specifying addresses using an offset is called relative addressing because the resulting address is relative to some other point. Another word for offset is displacement.

(2) In desktop publishing, the offset is the amount of space along the edge of the paper. Its purpose is to allow room for the binding. The offset is sometimes called the gutter.


offset printing

A printing technique whereby ink is spread on a metal plate with etched images, and then transferred to paper by pressing the paper against the plate. Most print shops use offset printing to produce large volumes of high-quality documents. Although the equipment and set-up costs are relatively high, the actual printing process is relatively inexpensive.

Desktop publishing generally involves producing documents on the computer, printing out drafts on a laser printer, and then offset printing the final version. To produce the plates used in offset printing, a print shop requires either film or high-resolution paper output, which the printer can then photograph. You can obtain either by taking a PostScript file to a service bureau.


OLE

Abbreviation of Object Linking and Embedding, pronounced oh-leh. OLE is a compound document standard developed by Microsoft Corporation. It enables you to create objects with one application and then link or embed them in a second application. Embedded objects retain their original format and links to the application that created them.

Support for OLE is built into the Windows and Macintosh operating systems. A competing compound document standard developed jointly by IBM, Apple Computer, and other computer firms is called OpenDoc.


on-board

Literally, on a circuit board. On-board memory, for example, refers to memory chips on the motherboard. On-board modems are modems that are on expansion boards.


on-board modem

Another term for an internal modem; that is, a modem that comes as an expansion board you can insert into a computer.


on-line

Turned on and connected. For example, printers are online when they are ready to receive data from the computer. You can also turn a printer off-line. While the printer is off-line, you can perform certain tasks such as advancing the paper, but you cannot send data to it. Most printers have an on-line button you can press to turn the machine on- or off-line.

Users are considered on-line when they are connected to a computer service through a modem. That is, they are actually on the line.


online help

See under help.


online service

A business that provides its subscribers with a wide variety of data transmitted over telecommunications lines. Online services provide an infrastructure in which subscribers can communicate with one another, either by exchanging e-mail messages or by participating in online conferences (forums). In addition, the service can connect users with an almost unlimited number of third-party information providers. Subscribers can get up-to-date stock quotes, news stories hot off the wire, articles from many magazines and journals, in fact, almost any information that has been put in electronic form. Of course, accessing all this data carries a price.

The difference between an online service and a bulletin board service is one of scale and profits. Online services provide a variety of information and services, whereas BBS’s normally concentrate on a single theme. In addition, BBS’s are often operated on a non-profit basis whereas online services are always for profit. Two of the largest online services are CompuServe and Prodigy.

One online service that defies classification is the Internet. In terms of users, it is the largest service, but it is not centrally controlled by any one organization, nor is it operated for profit.


OOP

See object-oriented programming.


OOPL

Stands for object-oriented programming language.


open

(v) To make an object accessible. Whenever you access a file (that is, you edit a text file or run a program file), the operating system opens the file. Opening a file can be simple or complex depending on the operating system. For example, in a multiprocessing operating system, in which different users can share the same resources, the operating system must decide whether the file can be accessed simultaneously by more than one user, and if so, it must ensure that different users do not try to modify the file's contents at the same time.

(adj) Accessible. When used to describe designs or architectures, open means public. See under open architecture.


open architecture

An architecture whose specifications are public. This includes officially approved standards as well as privately designed architectures whose specifications are made public by the designers. The opposite of open is closed or proprietary.

The great advantage of open architectures is that anyone can design add-on products for it. By making an architecture public, however, a manufacturer allows others to duplicate its product. The IBM PC, for example, was based on open architectures, and has spawned an entire industry of IBM clones. In contrast, the Macintosh architecture and operating system was predominantly closed until recently.


OpenDoc

A standard and application programming interface (API) that makes it possible to design independent programs (components) that can work together on a single document. OpenDoc is being developed by a loose alliance of companies, including Apple Computer, IBM, and Lotus. Notably absent from this list is Microsoft, which is pushing an alternative standard and API called Object Linking and Embedding (OLE).


operand

In all computer languages, expressions consist of two types of components: operands and operators. Operands are the objects that are manipulated and operators are the symbols that represent specific actions. For example, in the expression

5 + x

x and 5 are operands and + is an operator. All expressions have at least one operand.


operating environment

The environment in which users run programs. For example, the DOS environment consists of all the DOS commands available to users. The Macintosh environment, on the other hand, is a graphical user interface that uses icons and menus instead of commands.

There is a thin line between operating environments and shells. Historically, shells are the interfaces to operating systems. They do not actually add any new capabilities; they simply provide a better user interface. So-called intelligent shells, however, actually extend an operating system’s capabilities, so there is little difference between intelligent shells and operating environments.

Operating environments are sometimes called control programs.


operating system

The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop—it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

Operating systems can be classified as follows:

multi-user: Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.

multiprocessing: Supports running a program on more than one CPU.

multitasking: Allows more than one program to run concurrently.

multithreading: Allows different parts of a single program to run concurrently.

real-time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.

Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Xenix.

As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.


operator

(1) A symbol that represents a specific action. For example, a plus sign (+) is an operator that represents addition. The basic mathematic operators are

Operator	Action
+	addition
-	subtraction
*	multiplication
/	division
In addition to these operators, many programs and programming languages recognize other operators that allow you to manipulate numbers and text in more sophisticated ways. For example, Boolean operators enable you to test the truth or falsity of conditions, and relational operators let you compare one value to another.

(2) A computer operator is an individual who is responsible for mounting tapes and disks, making backups, and generally ensuring that a computer runs properly.


optical character recognition

Often abbreviated OCR, optical character recognition refers to the branch of computer science that involves reading text from paper and translating the images into a form that the computer can manipulate (for example, into ASCII codes). An OCR system enables you to take a book or a magazine article and feed it directly into an electronic computer file.

All OCR systems include an optical scanner for reading text, and sophisticated software for analyzing images. Most OCR systems use a combination of hardware (specialized circuit boards) and software to recognize characters, although some inexpensive systems do it entirely through software. Advanced OCR systems can read text in large variety of fonts, but they still have difficulty with handwritten text.

The potential of OCR systems is enormous because they enable users to harness the power of computers to access printed documents. OCR is already being used widely in the legal profession, where searches that once required hours or days can now be accomplished in a few seconds.


optical disk

A storage medium from which data is read and to which it is written by lasers. Optical disks can store much more data—up to 6 gigabytes (6 billion bytes)—than magnetic media, such as floppies and hard disks. There are three basic types of optical disks:

CD-ROM: Like audio CDs, CD-ROMs come with data already encoded onto them. The data is permanent and can be read any number of times, but CD-ROMs cannot be modified.

WORM: Stands for write-once, read-many. With a WORM disk drive, you can write data onto a WORM disk, but only once. After that, the WORM disk behaves just like a CD-ROM.

erasable: Optical disks that can be erased and loaded with new data, just like magnetic disks. These are often referred to as EO (erasable optical) disks.

These three technologies are not compatible with one another; each requires a different type of disk drive and disk. Even within one category, there are many competing formats, although CD-ROMs are relatively standardized.


optical fiber

See under fiber optics.


optical mouse

See under mouse.


optical scanner

A device that can read text or illustrations printed on paper and translate the information into a form the computer can use. A scanner works by digitizing an image—dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. (For color and gray scaling, the same principle applies, but each box is then represented by up to 24 bits.) The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen, and manipulated by programs.

Optical scanners do not distinguish text from illustrations; they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR) system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages.

Scanners differ from one another in the following respects:

scanning technology: Most scanners use charge-coupled device (CCD) arrays, which consist of tightly packed rows of light receptors that can detect variations in light intensity and frequency. The quality of the CCD array is probably the single most important factor affecting the quality of the scanner. Industry-strength drum scanners use a different technology that relies on a photomultiplier tube (PMT), but this type of scanner is much more expensive than the more common CCD-based scanners.

resolution: The denser the bit map, the higher the resolution. Typically, scanners support resolutions of from 72 to 600 dpi.

bit depth: The number of bits used to represent each pixel. The greater the bit depth, the more colors or grayscales can be represented. For example, a 24-bit color scanner can represent 224 (16.7 million) colors. Note, however, that a large color range is useless if the CCD arrays are capable of detecting only a small number of distinct colors.

size and shape: Some scanners are small hand-held devices that you move across the paper (Error! Reference source not found.). These hand-held scanners are often called half-page scanners because they can only scan 2 to 5 inches at a time. Hand-held scanners are adequate for small pictures and photos, but they are difficult to use if you need to scan an entire page of text or graphics.

Larger scanners include machines into which you can feed sheets of paper. These are called sheet-fed scanners. Sheet-fed scanners are excellent for loose sheets of paper, but they are unable to handle bound documents.

A second type of large scanner, called a flatbed scanner, is like a photocopy machine. It consists of a board on which you lay books, magazines, and other documents that you want to scan.

Overhead scanners (also called copyboard scanners) look somewhat like overhead projectors. You place documents faceup on a scanning bed, and a small overhead tower moves across the page.


optimize

(1) In programming, to fine-tune a program so that it runs more quickly or takes up less space.

(2) When applied to disks, the term means the same as defragment. See under fragmentation.


option

(1) In command-driven interfaces, an option is an addition to a command that changes or refines the command in a specified manner. As the term implies, options are just that—they are not required.

In the DOS operating system, options are preceded by a slash (/). For example the DIR command supports the /P option, which causes the system to pause between screenfuls of data. Other operating systems and applications have different rules for specifying options.

Another word for option is switch.

(2) In graphical user interfaces, an option is a choice in a menu or dialog box.


Option key

A key on Macintosh keyboards that you use in concert with other keys to generate special characters and commands. On PCs, the corresponding key is called an Alt key.


opto-mechanical mouse

See under mouse.


OR operator

A Boolean operator that returns a value of TRUE if either of its operands is TRUE. This is called an inclusive OR operator. There is also an exclusive OR operator (often abbreviated XOR) that returns a value of TRUE only if both operands have different values.


orientation

See under landscape and portrait.


original equipment manufacturer

See OEM.


orphan

In word processing, an orphan is the first line of a paragraph that appears as the last line of a page, or the last line of a paragraph that appears as the first line of a page (this is sometimes called a widow). Orphans are considered bad form in page layout, so most word processors allow you to avoid them.


OS/2

An operating system for PCs developed originally by Microsoft Corporation and IBM, but now sold and managed solely by IBM. OS/2 is compatible with DOS and Windows, which means that it can run all DOS and Windows programs. However, programs written specifically to run under OS/2 will not run under DOS or Windows.

Since its introduction in the late 80s, OS/2 has traveled a particularly rocky road. The first releases were hampered by a number of technical and marketing problems. Then Microsoft abandoned the project in favor of its own operating system solution, Microsoft Windows. That break spawned a feud between the two computer giants that is still being played out in many arenas.

In terms of technology, the latest versions of OS/2 and Windows are remarkably similar. Both are full 32-bit, multitasking operating systems that can run DOS and Windows applications. Microsoft Windows has the momentum, however, and it remains to be seen whether OS/2 will survive the 90s.


outline font

A scalable font in which the outlines of each character are geometrically defined. The most popular languages for defining outline fonts are PostScript and TrueType.

An outline font is scalable because, given a geometrical description of a typeface, a printer or other display device can generate the characters at any size (scale). Aside from offering innumerable sizes of each font, outline fonts have the added advantage that they make the most of an output device's resolution. The more resolution a printer or monitor offers, the better an outline font will look.


output

(n) Anything that comes out of a computer. Output can be meaningful information or gibberish, and it can appear in a variety of forms—as binary  numbers, as characters, as pictures, and as printed pages. Output devices include display screens, loudspeakers, and printers.

(v) To give out. For example, display screens output images, printers output print, and loudspeakers output sounds.


output device

Any machine capable of representing information from a computer. This includes display screens, printers, plotters, and synthesizers.


OverDrive

A user-installable microprocessor from Intel. Many PCs are built with an OverDrive socket, which allows the owner to upgrade to a faster microprocessor simply by inserting an OverDrive chip.


overflow error

An error that occurs when the computer attempts to handle a number that is too large for it. Every computer has a well-defined range of values that it can represent. If during execution of a program it arrives at a number outside this range, it will experience an overflow error. Overflow errors are sometimes referred to as overflow conditions.


overlaid windows

Windows arranged so that they overlap each other. Overlaid windows resemble a stack of pieces of paper lying on top of one another; only the topmost window is displayed in full. You can move a window to the top or bottom of the stack by clicking one of the mouse buttons. This is known as popping or pushing, respectively.

Overlaid windows are also called cascading windows. Windows that do not overlap are called tiled windows.


overstrike

To print one character directly on top of another. In older printers, this was one way to create unusual characters, but it is not necessary with modern printers.


overwrite mode

Most word processors and text editors allow you to choose between two modes: overwrite and insert. In overwrite mode, every character you type is displayed at the cursor position. If a character is already at that position, it is replaced. In insert mode, each character you type is inserted at the cursor position. This means that existing characters are moved over to make room for the new character, but they are not replaced.

Overwrite mode is sometimes called overtype mode.


pack

To compress data.


packed file

A file in a compressed format. Many operating systems and applications contain commands that enable you to pack a file so that it takes up less memory. For example, suppose you have a text file containing ten consecutive space characters. Normally, this would require ten bytes of storage. However, a program that packs files would replace the space characters by a special space-series character followed by the number of spaces being replaced. In this case, the ten spaces would require only two bytes. This is just one packing technique—there are many others. One disadvantage of packed files, however, is that they can be read only by the program that packed them because they contain special codes.

Some modems automatically pack data before transmitting it across communications lines. This can produce faster communication because fewer bytes need to be sent. However, the modem on the receiving side must be capable of unpacking the data.

Packing is often referred to as data compression, particularly when it involves data communications.


pad character

A character used to fill empty space. Many applications have fields that must be a particular length. For example, in a database application, you may have a field that is ten characters in length. If you use only four of the allotted characters, the program itself must fill in the remaining six characters with pad characters.

Some applications allow you to choose the character to be used as padding.


padding

Filling in unused space.


page

(n) (1) A fixed amount of data.

(2) In word processing, a page of text. Most text-processing applications recognize a hierarchy of components, starting with a character at the lowest level, followed by a word, a line, a paragraph, and a page. Applications permit certain operations for each type of component; for example, you can delete a character, a word, a line, and sometimes an entire page. For pages, you can also specify formatting characteristics (for example, page size, margins, and number of columns).

(3) In virtual memory systems, a page is a fixed number of bytes recognized by the operating system.

(4) Short for web page.

(v) (1) To display one page (or screenful) of a document at a time. To contrast, see scroll.

(2) To copy a page of data from main memory to a mass storage device, or vice versa. Paging is one form of swapping.


page break

The end of a page of text. In word-processing systems, you can enter special codes, called hard page breaks or forced page breaks, that cause the printer to advance to the next page. Without hard page breaks, the word processor automatically begins a new page after a page has been filled (this depends on the number of lines per page). In this case, the page break is called a soft page break.


Page Description Language (PDL)

A language for describing the layout and contents of a printed page. The best-known PDLs are Adobe PostScript and Hewlett-Packard PCL (Printer Control Language), both of which are used to control laser printers.

Both PostScript and modern versions of PCL are object-oriented, meaning that they describe a page in terms of geometrical objects such as lines, arcs, and circles.


Page Down key

Often abbreviated PgDn, the Page Down key is standard on PC and Macintosh keyboards. Its meaning differs from one program to another, but it usually moves the cursor down a set number of lines.


page eject

Same as form feed.


page fault

See under paging.


page layout program

A program that enables you to format pages of text and graphics. Many word-processing systems support their own page layout functions, but page layout applications designed specifically for this purpose generally give you more control over fine points such as text flow, kerning, and positioning of graphics.


page preview

See under preview.


page printer

Any printer that processes an entire page at one time. All laser and ink-jet printers are page printers, which means that they must have enough memory to store at least one page.


Page Up key

Often abbreviated PgUp, the Page Up key is standard on PC and Macintosh keyboards. Its meaning differs from one program to another, but it usually scrolls the document up one screenful.


page-mode memory

A special type of RAM divided into discrete sections, called pages. Within any page of memory, the CPU can access memory quickly without resorting to wait states. Typically, a page is 2K bytes.


page-white display

A special type of LCD display screen that uses supertwist technology to produce a high contrast between the foreground and background.


pages per minute

See ppm.


pagination

(1) Refers to numbering pages in a document.

(2) Refers to dividing a document into pages. Most word processors automatically paginate documents based on a page size that you specify. Some word processors enable you to avoid widows and orphans during pagination.


paging

A technique used by virtual memory operating systems to help ensure that the data you need is available as quickly as possible. The operating system copies a certain number of pages from your storage device to main memory. When a program needs a page that is not in main memory, the operating system copies the required page into memory and copies another page back to the disk. One says that the operating system pages the data. Each time a page is needed that is not currently in memory, a page fault occurs.

This type of virtual memory is called paged virtual memory. Another form of virtual memory is segmented virtual memory.


paint program

A graphics program that enables you to draw pictures on the display screen which are represented as bit maps (bit-mapped graphics). In contrast, draw programs use vector graphics (object-oriented images), which scale better.

Most paint programs provide the tools listed in Table:Paint tools in the form of icons. By selecting an icon, you can perform functions associated with the tool.

In addition to these tools, paint programs also provide easy ways to draw common shapes such as straight lines, rectangles, circles, and ovals.


palette

(1) In computer graphics, a palette is the set of available colors. For a given application, the palette may be only a subset of all the colors that can be physically displayed. For example, a SVGA system can display 16 million unique colors, but a given program may use only 256 of them at a time. The computer system’s palette, therefore, would consist of the 16 million colors, but the program’s palette would contain only the 256-color subset.

On monochrome systems, the term palette is sometimes used to refer to the available fill patterns.

(2) In paint and illustration programs, a palette is a collection of symbols that represent drawing tools. For example, a simple palette might contain a paintbrush, a pencil, and an eraser.


palmtop

A small computer that literally fits in your palm. Compared to full-size computers, palmtops are severely limited, but they are practical for certain functions such as phone books and calendars. Palmtops that use a pen rather than a keyboard for input are often called hand-held computers or PDAs.

Because of their small size, most palmtop computers do not include disk drives. However, many contain PCMCIA slots in which you can insert disk drives, modems, memory, and other devices.


Pantone Matching System (PMS)

A popular color matching system used by the printing industry to print spot colors. Most applications that support color printing allow you to specify colors by indicating the Pantone name or number. This assures that you get the right color when the file is printed, even though the color may not look right when displayed on your monitor.

PMS works well for spot colors but not for process colors, which are generally specified using the CMYK color model.


paper feed

The mechanism or method that moves paper through a printer. For example, a tractor-feed mechanism is one that pulls the paper with a rotating wheel whose nubs catch in holes on either side of the paper.


paper-white display

A high-quality monochrome monitor that displays characters in black against a white background. Such monitors are popular for desktop publishing because they most closely mimic real paper with black type. Some manufacturers make a distinction between normal white-background monitors and paper-white monitors, where the background is slightly tinted to look more like bonded paper.


paperless office

The idealized office in which paper is absent because all information is stored and transferred electronically. With the ever-expanding application of computers into business areas as diverse as accounting, desktop publishing, billing, mail, and scheduling, it seemed in the early 80s that the real paperless office was just around the corner. Ironically, just the opposite has transpired. The ease with which computers enable people to print all sorts of documents has created a flood of new paper. Indeed, perhaps the most widespread computer application is the fax machine, which uses paper by the roll.

Some analysts believe that the paperless office is still an achievable and laudable goal, but that certain key technologies such as optical character recognition (OCR) must be improved. Others, however, argue that the tangibleness of paper documents yields certain benefits that will never disappear.


parallel

Refers to processes that occur simultaneously. Printers and other devices are said to be either parallel or serial. Parallel means the device is capable of receiving more than one bit at a time (that is, it receives several bits in parallel). Most modern printers are parallel.


parallel interface

A channel capable of transferring more than one bit simultaneously. Almost all personal computers come with at least one parallel interface that is reserved for connecting a printer. The other type of interface is a serial interface.


parallel port

A parallel interface for connecting an external device such as a printer. Most personal computers have both a parallel port and at least one serial port.

On PCs, the parallel port uses a 25-pin connector (type DB-25) and is used almost exclusively to connect printers. It is often called a Centronics interface after the company that designed the original standard for parallel communication between a computer and printer. (The modern parallel interface is based on a design by Epson.)

A newer type of parallel port, which supports the same connectors as the Centronics interface, is the EPP (Enhanced Parallel Port) or ECP (Extended Capabilities Port). Both of these parallel ports support bi-directional communication and transfer rates ten times as fast as the Centronics port.

Macintoshes have SCSI and LocalTalk ports, which are parallel, but are more flexible. They are used for many types of communication in addition to connecting printers.


parallel processing

The simultaneous use of more than one CPU to execute a program. Ideally, parallel processing makes a program run faster because there are more engines (CPUs) running it. In practice, it is often difficult to divide a program in such a way that separate CPUs can execute different portions without interfering with each other.

Most computers have just one CPU, but some models have several. There are even computers with thousands of CPUs. With single-CPU computers, it is possible to perform parallel processing by connecting the computers in a network. However, this type of parallel processing requires very sophisticated software called distributed processing software.

Note that parallel processing differs from multitasking, in which a single CPU executes several programs at once.


parameter

(1) Characteristic. For example, specifying parameters means defining the characteristics of something. In general, parameters are used to customize a program. For example, filenames, page lengths, and font specifications could all be considered parameters.

(2) In programming, the term parameter is synonymous with argument, a value that is passed to a routine.


parameter RAM (PRAM)

See PRAM.


parent directory

Refers to the directory above another directory. Every directory, except the root directory, lies beneath another directory. The higher directory is called the parent directory, and the lower directory is called a subdirectory. In DOS and UNIX systems, the parent directory is identified by two dots (. .).


parity

The quality of being either odd or even. The fact that all numbers have a parity is commonly used in data communications to ensure the validity of data. This is called parity checking.


parity bit

See under parity checking.


parity checking

In communications, parity checking refers to the use of parity bits to check that data has been transmitted accurately. The parity bit is added to every seven bits that are transmitted. The parity bit for each byte (seven data bits plus a parity bit) is set so that all bytes have either an odd number or an even number of set bits.

Assume, for example, that two devices are communicating with even parity (the most common form of parity checking). As the transmitting device sends data, it counts the number of set bits in each group of seven bits. If the number of set bits is even, it sets the parity bit to 0; if the number of set bits is odd, it sets the parity bit to 1. In this way, every byte has an even number of set bits. On the receiving side, the device checks each byte to make sure that it has an even number of set bits. If it finds an odd number of set bits, the receiver knows there was an error during transmission.

The sender and receiver must both agree to use parity checking and to agree on whether parity is to be odd or even. If the two sides are not configured with the same parity sense, communication will be impossible.

Parity checking is the most basic form of error detection in communications. Although it detects many errors, it is not foolproof, because it cannot detect situations in which two or four consecutive bits are changed due to electrical noise. There are many other more sophisticated protocols for ensuring transmission accuracy, such as MNP and CCITT V.42.

Parity checking is used not only in communications but also to test memory storage devices. Many PCs, for example, perform a parity check on memory every time you boot the machine.


park

To lock the read/write head of a hard disk drive in a safe position so that the disk will not be damaged while moving the drive. Parking the disk is particularly important for portable computers, which are moved frequently. The disk will automatically unpark itself once you turn the power on.

Most modern disk drives support automatic head parking, in which the drive automatically parks the head whenever the power is turned off.


partition

(v) To divide memory or mass storage into isolated sections. In DOS systems, you can partition a disk, and each partition will behave like a separate disk drive. Partitioning is particularly useful if you run more than one operating system. For example, you might reserve one partition for DOS and another for UNIX.

On Apple Macintosh computers, there are two types of partitioning: hard and soft. Hard partitioning is the same as DOS partitioning—the disk is physically divided into different sections. Soft partitioning, on the other hand, does not physically affect the disk at all, but it fools the Finder into believing that the disk is partitioned. The advantage of this is that you can partition the disk without affecting the data on it. With hard partitioning, it is usually necessary to reformat the entire disk.

(n) A section of main memory or mass storage that has been reserved for a particular application.


Pascal

Pronounced pass-kal, a high-level programming language developed by Niklaus Wirth in the late 1960s. The language is named after Blaise Pascal, a seventeenth-century French mathematician who constructed one of the first mechanical adding machines.

Pascal is best known for its affinity to structured programming techniques. The nature of the language forces programmers to design programs methodically and carefully. For this reason, it is a popular teaching language.

Despite its success in academia, Pascal has had only modest success in the business world. Part of the resistance to Pascal by professional programmers stems from its inflexibility and lack of tools for developing large applications.

To address some of these criticisms, Wirth designed a new language called Modula-2. Modula-2 is similar to Pascal in many respects, but it contains additional features.


passive-matrix display

A common type of flat-panel display consisting of a grid of horizontal and vertical wires. At the intersection of each grid is an LCD element which constitutes a single pixel, either letting light through or blocking it. A higher quality and more expensive type of display, called an active-matrix display, uses a transistor to control each pixel.


password

A secret series of characters that enables a user to access a file, computer, or program. On multi-user systems, each user must enter his or her password before the computer will respond to commands. The password helps ensure that unauthorized users do not access the computer. In addition, data files and programs may require a password.

Ideally, the password should be something that nobody could guess. In practice, most people choose a password that is easy to remember, such as their name or their initials. This is one reason it is relatively easy to break into most computer systems.


paste

To copy an object from a buffer (or clipboard) to a file. In word processing, blocks of text are moved from one place to another by cutting and pasting. When you cut  a block of text, the word processor removes the block from your file and places it in a temporary holding area (a buffer). You can then paste the material in the buffer somewhere else.

Modern operating systems, such as Microsoft Windows, allow you to cut  an object from one application and paste it into another. Depending on how the object is pasted, it can be either linked or embedded.


patch

A temporary fix to a program bug. A patch is an actual piece of object code that is inserted into (patched into) an executable program.


path

(1) In DOS systems, a path is a list of directories where the operating system looks for executable files if it is unable to find the file in the working directory. You can specify the list of directories with the PATH command.

(2) Another name for pathname.


pathname

A sequence of symbols and names that identifies a file. Every file has a name, called a filename, so the simplest type of pathname is just a filename. If you specify a filename as the pathname, the operating system looks for that file in your current  working directory. However, if the file resides in a different directory, you must tell the operating system how to find that directory. You do this by specifying a path that the operating system must follow.

The pathname always starts from your working directory or from the root directory. Each operating system has its own rules for specifying paths. In DOS systems, for example, the root directory is named \, and each subdirectory is separated by an additional backslash. In UNIX, the root directory is named /, and each subdirectory is followed by a slash. In Macintosh environments, directories are separated by a colon.


pattern recognition

An important field of computer science concerned with recognizing patterns, particularly visual and sound patterns. It is central to optical character recognition (OCR), voice recognition, and handwriting recognition.


Pause key

A key that you can use to temporarily halt the display of data. Generally, you use the Pause key to freeze data that is being scrolled on the display screen. To continue scrolling, you can press any key.

In DOS, an alternative to using the Pause key is to use the MORE command, which displays one screenful of data at a time.


PC

(1) Short for personal computer or IBM PC. The first personal computer produced by IBM was called the PC, and increasingly the term PC came to mean IBM or IBM-compatible personal computers, to the exclusion of other types of personal computers, such as Macintoshes.

In recent years, the term PC has become more and more difficult to pin down. In general, though, it applies to any personal computer based on an Intel microprocessor, or on an Intel-compatible microprocessor. For nearly every other component, including the operating system, there are several options, all of which fall under the rubric of PC:

Expansion bus: ISA, EISA, or MCA

Local bus: VL-Bus or PCI

Mass storage interface: IDE, ESDI, or SCSI.

Operating system: DOS, Windows, or OS/2.

Video standard: VGA, SVGA, or 8514/A.

(2) PC can stand for printed circuit, so a PC board is a printed circuit board.


PC card

A computer device packaged in a small card about the size of a credit card and conforming to the PCMCIA standard.


PC fax

Same as fax modem.


PC-DOS

The name IBM uses to market the DOS operating system developed by Microsoft.


PC/AT

See under AT.


PCB

Short for printed circuit board.


PCI

Acronym for Peripheral Component Interconnect, a local bus standard developed by Intel Corporation. Most modern PCs include a PCI bus in addition to a more general ISA expansion bus. Many analysts, however, believe that PCI will eventually supplant ISA entirely. In addition, Apple computer has indicated that future versions of the PowerMac will use PCI.

PCI Version 1.0 is a 32-bit bus that runs at a clock speed of 33 MHz. This yields a throughput rate of 132 megabytes per second. PCI 2.0 is a 64-bit bus running at a clock speed of 66MHz.

Although it was developed by Intel, PCI is not tied to any particular family of microprocessors. In fact, in a strict sense, it is not a local bus at all because it does not connect directly with the microprocessor. For this reason, some people call it a mezzanine bus.


PCL

Abbreviation of Printer Control Language, the page description language (PDL) developed by Hewlett Packard and used in many of their laser and ink-jet printers. PCL 5 and later versions support a scalable font technology called Intellifont.


PCMCIA

Short for Personal Computer Memory Card International Association, and pronounced as separate letters, PCMCIA is an organization consisting of some 500 companies that has developed a standard for small, credit card-sized devices, called PC Cards. Originally designed for adding memory to portable computers, the PCMCIA standard has been expanded several times and is now suitable for many types of devices. There are in fact three types of PCMCIA cards. All three have the same rectangular size (85.6 by 54 millimeters), but different widths

•	Type I cards can be up to 3.3 mm thick, and are used primarily for adding additional ROM or RAM to a computer.

•	Type II cards can be up to 5.5 mm thick. These cards are often used for modem and fax modem cards.

•	Type III cards can be up to 10.5 mm thick, which is sufficiently large for portable disk drives.

As with the cards, PCMCIA slots also come in three sizes:

•	A Type I slot can hold one Type I card

•	A Type II slot can hold one Type II card or two Type I cards

•	A Type III slot can hold one Type III card or a Type I and Type II card.

Ideally, you should be able to exchange PC Cards on the fly, without rebooting your computer. For example, you should be able to slip in a fax modem card when you want to send a fax and then, when you’re done, replace the fax modem card with a memory card. Unfortunately, because of deficiencies in the initial standard and poor implementations by card manufacturers, this has sometimes not worked as planned. However, the standard appears to be reaching a level of maturity where such plug-and-play installation is becoming a reality.

Some analysts believe that the PC card has the potential to become the dominant expansion technology for desktop model computers as well as portable computers.


PCX

Originally developed by ZSOFT for its PC Paintbrush program, PCX is a graphics file format for graphics programs running on PCs. It is supported by most optical scanners, fax programs, and desktop publishing systems. Files in the PCX format end with a “.pcx” ( pronounced dot-p-c-x) extension. Two other common bit map formats are BMP and TIFF.


PDA

Short for personal digital assistant, a handheld device that combines computing, telephone/fax, and networking features. A typical PDA can function as a cellular phone, fax sender, and personal organizer. Unlike portable computers, most PDAs are pen-based, using a stylus rather than a keyboard for input. This means that they also incorporate handwriting recognition features. Some PDAs can also react to voice input by using voice recognition technologies.

The field of PDA was pioneered by Apple Computer, which introduced the Newton MessagePad in 1993. Shortly thereafter, several other manufacturers offered similar products. To date, PDAs have had only modest success in the marketplace, due to their high price tags and limited applications. However, many experts believe that PDAs will eventually become common gadgets.


PDL

See page description language.


peer-to-peer architecture

A type of network in which each workstation has equivalent capabilities and responsibilities. This differs from client/server architectures, in which some workstations are dedicated to serving the others. Peer-to-peer networks are generally simpler and less expensive, but they usually do not offer the same performance under heavy loads.


pel

Short for pixel.


pen computer

A computer that utilizes an electronic pen (called a stylus) rather than a keyboard for input. Pen computers require special operating systems that support handwriting recognition so that users can write on the screen or on a tablet instead of typing on a keyboard. Most pen computers are hand-held devices, which are too small for a full-size keyboard.


Pentium microprocessor

See under Intel microprocessors.


Pentium Pro

The Pentium Pro is Intel's sixth generation microprocessor. Although, it shares the s\ame name as the fifth-generation Pentium microprocessor, the Pentium Pro is architecturally quite different. Thanks to modern design techniques, including superpipelining, dynamic execution, and on-chip L2 cache, the Pentium Pro can perform at nearly twice the speed of the Pentium microprocessors.


peripheral

Short for peripheral device.


Peripheral Component Interconnect

See PCI.


peripheral device

Any external device attached to a computer. Examples of peripherals include printers, disk drives, display monitors, keyboards, and mice.


personal computer

A small, relatively inexpensive computer designed for an individual user. In price, personal computers range anywhere from a few hundred dollars to over five thousand dollars. All are based on the microprocessor technology that enables manufacturers to put an entire CPU on one chip. Businesses use personal computers for word processing, accounting, desktop publishing, and for running spreadsheet and database management applications. At home, the most popular use for personal computers is for playing games.

Personal computers first appeared in the late 1970s. One of the first and most popular personal computers was the Apple II, introduced in 1977 by Apple Computer. During the late 1970s and early 1980s, new models and competing operating systems seemed to appear daily. Then, in 1981, IBM entered the fray with its first personal computer, known as the IBM PC. The IBM PC quickly became the personal computer of choice, and most other personal computer manufacturers fell by the wayside. One of the few companies to survive IBM's onslaught was Apple Computer, which remains a major player in the personal computer marketplace.

Other companies adjusted to IBM's dominance by building IBM clones, computers that were internally almost the same as the IBM PC, but that cost less. Because IBM clones used the same microprocessors as IBM PCs, they were capable of running the same software. Over the years, IBM has lost much of its influence in directing the evolution of PCs. Many of its innovations, such as the MCA expansion bus and the OS/2 operating system, have not been accepted by the industry or the marketplace.

Today, the world of personal computers is basically divided between Apple Macintoshes and PCs. The principal characteristics of personal computers are that they are single-user systems and are based on microprocessors. However, although personal computers are designed as single-user systems, it is common to link them together to form a network. In terms of power, there is great variety. At the high end, the distinction between personal computers and workstations has faded. High-end models of the Macintosh and PC offer the same computing power and graphics capability as low-end workstations by Sun, Hewlett-Packard, and DEC.


Personal Computer Memory Card International Association

See under PCMCIA.


Personal Digital Assistant

See PDA.


personal finance manager

A simple accounting program that helps individuals manage their finances. Personal finance managers help you balance your checkbook and keep track of investments. Some can even help you pay your bills by printing out checks or transferring money electronically from your bank account.


personal information manager

See PIM.


PGA

Short for pin grid array, a type of chip in which the connecting pins are located on the bottom in concentric squares. PGA chips are particularly good for chips that have many pins, such as modern microprocessors. Compare with DIP and SIP.


PgDn key

See Page Down key.


PgUp key

See Page Up key.


phase-change printer

Same as solid ink-jet printer.


Phoenix BIOS

Phoenix Corporation is the largest producer of BIOS chips for IBM PC clones.


photo illustration

A type of computer art that begins with a digitized photograph. Using special image enhancement software, the artist can then apply a variety of special effects to transform the photo into a work of art.


PhotoCD

A file format for storing digital photographs developed by Eastman Kodak Co.


physical

Refers to anything pertaining to hardware. The opposite of physical is logical or virtual, which describe software objects. For example, physical memory refers to the actual RAM chips installed in a computer. Virtual memory, on the other hand, is an imaginary storage area used by programs.

A physical data structure refers to the actual organization of data on a storage device. The logical data structure refers to how the information appears to a program or user. For example, a data file is a collection of information stored together. This is its logical structure. Physically, however, a file could be stored on a disk in several scattered pieces.


PIC

Short for Lotus Picture File, the graphics file format used to represent graphics generated by Lotus 1-2-3.


pica

In typesetting, a pica is a unit of measurement equal to 1/6 of an inch, or 12 points.


PICT file format

A file format developed by Apple Computer in 1984. PICT files are encoded in QuickDraw commands and can hold both object-oriented images and bit-mapped images. It is supported by all graphics programs that run on Macintosh computers.

The original PICT format supports 8 colors. A newer version of PICT, called PICT2, supports up to 256 colors.


pie chart

A type of presentation graphic in which percentage values are represented as slices of a pie.


PIM

Acronym for personal information manager, a type of software application designed to help users organize random bits of information. Although the category is fuzzy, most PIMs enable you to enter various kinds of textual notes—reminders, lists, dates — and to link these bits of information together in useful ways. Many PIMs also include calendar, scheduling, and calculator programs.


pin

(1) In dot-matrix printers, the devices that press on the ink ribbon to make dots on the paper. Printers are classified by how many pins they have on the printer head. The more pins a printer has, the higher-quality type it is capable of producing. Dot-matrix printers can have anywhere from 9 to 24 pins. A 24-pin printer can produce letter-quality print.

(2) A male lead on a connector.

(3) Silicon chips have an array of thin metal feet (pins) on their underside that enables them to be attached to a circuit board. The pins are very delicate and easily bent. If they are damaged, the chip will not sit correctly and will malfunction.


pin feed

Same as tractor feed.


pin grid array

See PGA.


pipe

A temporary software connection between two programs or commands. Normally, the operating system accepts input from the keyboard and sends output to the display screen. Sometimes, however, it is useful to use the output from one command as the input for a second command, without passing the data through the keyboard or display screen. Pipes were invented for these situations.

One of the best examples of pipe usage is linking the command that lists files in a directory to a command that sorts data. By piping the two commands together, you can display the files in sorted order. In UNIX and DOS, the pipe symbol is a vertical bar (|). The DOS command to list files in alphabetical order, therefore, would be:

DIR | SORT


pipelining

A technique used in advanced microprocessors where the microprocessor begins executing a second instruction before the first has been completed. That is, several instructions are in the “pipe” simultaneously, each at a different processing stage. Although formerly a feature only of high-performance and RISC-based microprocessors, pipelining is now common in microprocessors used in personal computers. Intel’s Pentium chip, for example, uses pipelining to execute as many as four instructions simultaneously.


piracy

See software piracy.


pitch

(1) For fixed-pitch (or monospaced) fonts, pitch refers to the number of characters printed per inch. Pitch is one characteristic of a monospaced font. Common pitch values are 10 and 12.

In proportional-pitch fonts, different characters have different widths, depending on their size. For example, the letter d would be wider than the letter I. Proportional fonts, therefore, have no pitch value.

(2) In graphics, dot pitch refers to the spacing between pixels on a monitor. The smaller the dot pitch, the sharper the image.


pixel

Short for Picture Element, a pixel is a single point in a graphic image. Graphics monitors display pictures by dividing the display screen into thousands (or millions) of pixels, arranged in rows and columns. The pixels are so close together that they appear connected.

The number of bits used to represent each pixel determines how many colors or shades of gray can be displayed. For example, an 8-bit color monitor uses 8 bits for each pixel, making it possible to display 28 (256) different colors or shades of gray.

On color monitors, each pixel is actually composed of three dots—a red, a blue, and a green one. Ideally, the three dots should all converge at the same point, but all monitors have some convergence error that can make color pixels appear fuzzy.

The quality of a display monitor largely depends on its resolution, how many pixels it can display, and how many bits are used to represent each pixel. VGA monitors display 640 by 480, or about 300,000 pixels. In contrast, SVGA monitors display 1,024 by 768, or nearly 800,000 pixels. True Color monitors use 24 bits per pixel, allowing them to display more than 16 million different colors.


PKZIP

One of the most widely used file compression methods. PKZIP was developed by PKWARE, Inc. in 1989 and distributed as shareware. Files that have been compressed using PKWARE are said to be zipped. Decompressing them is called unzipping.

The PK stands for Phillip Katz, the author of the programs.


plain text

Refers to textual data in ASCII format. Plain text is the most portable format because it is supported by nearly every application on every machine. It is quite limited, however, because it cannot contain any formatting commands.


plasma display

A type of flat-panel display that works by sandwiching an ionized gas between two wired panels. In one panel the wires are placed in vertical rows, and in the other they are placed in horizontal rows. Together, the two panels form a grid. An individual point (pixel) can then be charged by passing a current through the appropriate x-coordinate and y-coordinate wires. When the gas is charged, it glows a bright orange.


platform

The underlying hardware or software for a system. For example, the platform might be an Intel 80486 processor running DOS Version 6.0. The platform could also be UNIX machines on an Ethernet network.

The platform defines a standard around which a system can be developed. Once the platform has been defined, software developers can produce appropriate software and managers can purchase appropriate hardware and applications.

The term cross-platform refers to applications, formats, or devices that work on different platforms. For example, a cross-platform programming environment enables a programmer to develop programs for many platforms at once.


platter

A round magnetic plate that constitutes part of a hard disk. Hard disks typically contain two, four, or eight platters. Each platter requires two read/write heads, one for each side.


plot

To produce an image by drawing lines. You can program a computer to plot images on a display screen or on paper.


plotter

A device that draws pictures on paper based on commands from a computer. Plotters differ from printers in that they draw lines using a pen. As a result, they can produce continuous lines, whereas printers can only simulate lines by printing a closely spaced series of dots. Multicolor plotters use different-colored pens to draw different colors.

In general, plotters are considerably more expensive than printers. They are used in engineering applications where precision is mandatory.


plug

A connector used to link together devices.


plug compatible

Refers to a device's ability to connect to other devices made by a different manufacturer without any alterations. For example, many companies sell plug-compatible expansion boards for PCs. These are circuit boards that you can insert without modification into a PC to give the computer added capabilities.


plug-and-play

Refers to the ability of a computer system to automatically configure expansion boards and other devices. You should be able to plug in a device and play with it, without worrying about setting DIP switches, jumpers, and other configuration elements. Since the introduction of the NuBus, the Apple Macintosh has been a plug-and-play computer, while the PC has not. This may change, however, as manufacturers adopt the new Plug and Play (PnP) specification created by Microsoft and Intel in 1993.


PMS

See Pantone Matching System (PMS).


PnP

Short for Plug and Play, a technology developed by Microsoft and Intel that supports plug-and-play installation. PnP is built into the Windows 95 operating system, but to use it, the computer’s BIOS and expansion boards must also support PnP.


point

(v) To move the pointer on a display screen to select an item. Graphical user interfaces, such as the Macintosh interface, are often called point-and-click interfaces because a user typically points to an object on the screen and then clicks a button on the mouse.

(n) In typography, a point is about 1/72 of an inch and is used to measure the height of characters. (Historically, a point was .0138 inches, a little less than 1/72 of an inch, but this has changed.) This paragraph, for example, is printed in 9-point type.

The height of the characters is one characteristic of fonts. Some fonts are referred to as fixed-point fonts because their representation allows for only one size. In contrast, a scalable font is one that is represented in such a way that the size can easily be changed.


Point of Presence

See POP.


Point-to-Point Protocol

See PPP.


pointer

(1) In graphical user interfaces, a pointer is a small arrow or other symbol on the display screen that moves as you move the mouse. You can select commands and options by positioning the tip of the arrow over the desired choice and clicking a mouse button.

Many text processing programs use an I-beam pointer.

Pointers are often referred to as mouse pointers.

(2) In programming, a pointer is a special type of variable that holds a memory address (that is, it points to a memory location).


pointing device

A device with which you can control the movement of the pointer to select items on a display screen. Examples of pointing devices include mice, trackballs, joysticks, touchpads, and light pens.


pointing stick

A pointing device first developed by IBM for its notebook computers that consists of a miniature joystick, usually with a rubber eraser-head tip, positioned somewhere between the keys on the keyboard. Most pointing sticks are pressure-sensitive, so the pointer moves faster when more pressure is applied.


polling

Making continuous requests for data from another device. For example, modems that support polling can call another system and request data.


polyline

In computer graphics, a continuous line composed of one or more line segments. You can create a polyline by specifying the endpoints of each segment. In draw programs, you can treat a polyline as a single object, or divide it into its component segments.


pop

Given a stack of items, popping one of the items means to pull it off the stack. Although originally coined to describe manipulation of data stacks, the term is often used in connection with display windows. When two or more windows overlap, you can pop one of them so that it is the topmost window.

The opposite of pop is push, which means to move an object onto a stack.


POP

(1) Short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server.  Most e-mail applications (sometimes called a mail client) use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol).

There are two versions of POP. The first, called POP2, became a standard in the mid-80's and requires SMTP to send messages. The newer version, POP3, can be used with or without SMTP.

(2) Short for Point of Presence, a location where you can get dial-up access. Internet Service Providers (ISPs) generally provide many POPs so that users can make a local local to gain Internet access.


pop-up menu

See under menu.


pop-up utility

A program installed to be memory resident so that you can always execute it by pressing a special key, called a hot key. When you press the hot key, the pop-up utility appears, regardless of which application you are currently running. When you exit the pop-up utility, the system returns you to your previous program.

In DOS systems, pop-up utilities are also called TSRs.


pop-up window

A window that suddenly appears (pops up) when you select an option with a mouse or press a special function key. Usually, the pop-up window contains a menu of commands and stays on the screen only until you select one of the commands. It then disappears.

A special kind of pop-up window is a pull-down menu, which appears just below the item you selected, as if you had pulled it down.


port

(n) An interface on a computer to which you can connect a device. Personal computers have various types of ports. Internally, there are several ports for connecting disk drives, display screens, and keyboards. Externally, personal computers have ports for connecting modems, printers, mice, and other peripheral devices.

Almost all personal computers come with a serial RS-232C port or RS-422 port for connecting a modem or mouse and a parallel port for connecting a printer. On PCs, the parallel port is a Centronics interface that uses a 25-pin connector. SCSI (Small Computer System Interface) ports support higher transmission speeds than do conventional ports and enable you to attach up to seven devices to the same port. All Apple Macintosh computers since the Macintosh Plus have a SCSI port.

(v) To move a program from one type of computer to another. To port an application, you need to rewrite sections that are machine dependent, and then recompile the program on the new computer. Programs that can be ported easily are said to be portable.


portable

(1) When used to describe hardware, portable means small and lightweight. A portable computer is a computer small enough to carry. Portable computers include notebook and subnotebook computers, hand-held computers, palmtops, and PDAs.

(2) When used to describe software, portable means that the software has the ability to run on a variety of computers. Portable and machine independent mean the same thing—that the software does not depend on a particular type of hardware.


portrait

The terms portrait and landscape refer to different orientations of the paper—whether it is oriented vertically or horizontally. A page with portrait orientation, typical for letters, memos, and other text documents, is taller than it is wide.

Not all printers are capable of generating text in landscape mode.

Orientation is also a characteristic of monitors. Portrait monitors are often called full-page monitors.


post

(v) To publish a message in an online forum or newsgroup.

(n) A message published in an online forum or newsgroup.


Post Office Protocol

See POP.


PostScript

A page description language (PDL) developed by Adobe Systems. PostScript is primarily a language for printing documents on laser printers, but it can be adapted to produce images on other types of devices. PostScript is the standard for desktop publishing because it is supported by imagesetters, the very high-resolution printers used by service bureaus to produce camera-ready copy.

PostScript is an object-oriented language, meaning that it treats images, including fonts, as collections of geometrical objects rather than as bit maps. PostScript fonts are called outline fonts because the outline of each character is defined. They are also called scalable fonts because their size can be changed with PostScript commands. Given a single typeface definition, a PostScript printer can thus produce a multitude of fonts. In contrast, many non-PostScript printers represent fonts with bit maps. To print a bit-mapped typeface with different sizes, these printers require a complete set of bit maps for each size.

The principal advantage of object-oriented (vector) graphics over bit-mapped graphics is that object-oriented images take advantage of high-resolution output devices whereas bit-mapped images do not. A PostScript drawing looks much better when printed on a 600-dpi printer than on a 300-dpi printer. A bit-mapped image looks the same on both printers.

Every PostScript printer contains a built-in interpreter that executes PostScript instructions. If your laser printer does not come with PostScript support, you may be able to purchase a cartridge that contains PostScript.

There are two basic versions of PostScript: Level 1 and Level 2. Level 2 PostScript, which was released in 1992, has better support for color printing.


POTS

Short for plain old telephone service, and refers to the standard telephone service that most homes use. In contrast, telephone services based on high-speed, digital communications lines, such as ISDN and FDDI, are not POTS. The main distinctions between POTS and non-POTS services are speed and bandwidth. POTS is generally restricted to about 28.8 kbps (28,800 bits per second).


power down

To turn a machine off.


power supply

The component that supplies power to a computer. Most personal computers can be plugged into standard electrical outlets. The power supply then pulls the required amount of electricity and converts the AC current to DC current. It also regulates the voltage to eliminate spikes and surges common in most electrical systems. Not all power supplies, however, do an adequate voltage-regulation job, so a computer is always susceptible to large voltage fluctuations.

Power supplies are rated in terms of the number of watts they generate. The more powerful the computer, the more watts it can provide to components. In general, 200 watts should be sufficient.


power up

To turn a machine on.


power user

A sophisticated user of personal computers. A power user is typically someone who has considerable experience with computers and utilizes the most advanced features of applications.


PowerPC

A RISC-based computer architecture developed jointly by IBM, Apple Computer, and Motorola Corporation. The name is derived from IBM’s name for the architecture, Performance Optimization With Enhanced RISC.

The first computers based on the PowerPC architecture were the Power Macs, which appeared in 1994. Since then, other manufacturers, including IBM, have built PCs based on the PowerPC. Although the initial reviews have been good, it remains to be seen whether this new architecture can eventually supplant, or even coexist, with the huge number of Intel-based computers in use and on the market.

There are already a number of different operating systems that run on PowerPC-based computers, including the Macintosh operating system (System 7.5 and higher), Windows NT, and OS/2.


ppm

Stands for pages per minute and is used to measure the speed of certain types of printers, particularly laser printers. An average speed for laser printers printing text is 8 ppm.

Note that the ppm advertised for printers applies only to text. Complex graphics can slow a printer down considerably. Increasingly, the abbreviation gppm is being used for graphics pages per minute.


PPP

Short for Point-to-Point Protocol, a method of connecting a computer to the Internet. PPP is more stable than the older SLIP protocol and provides error checking features.


PRAM

Pronounced pee-ram, short for parameter RAM. On Macintosh computers, PRAM is a small portion of RAM used to store information about the way the system is configured. For example, parameter RAM holds the date and time, desktop pattern, mouse settings, volume settings, and other control data set with control panels. Parameter RAM is powered by a battery, so it does not lose its contents when the power is turned off.


precedence

A characteristic of operators that indicates when they will be evaluated when they appear in complex expressions. Operators with high precedence are evaluated before operators with low precedence. For example, the multiplication operator (*) has higher preference than the addition operator (+), so the expression

2+3*4

equals 14, not 20.

You can override precedence rules by surrounding parts of an expression with parentheses. For example,

(2+3)*4

would evaluate to 20.


precision

When used to describe floating-point numbers, precision refers to the number of bits used to hold the fractional part. The more precision a system uses, the more exactly it can represent fractional quantities.

Floating-point numbers are often classified as single precision or double precision. A double-precision number uses twice as many bits as a single-precision value, so it can represent fractional quantities much more exactly.


preemptive multitasking

See under multitasking.


prepress service bureau

See under service bureau.


presentation graphics

A type of business software that enables users to create highly stylized images for slide shows and reports. The software includes functions for creating various types of charts and graphs and for inserting text in a variety of fonts. Most systems enable you to import data from a spreadsheet application to create the charts and graphs.

Presentation graphics is often called business graphics.


preview

In word processing, previewing refers to formatting a document for the printer, but then displaying it on the display screen instead of printing it. Previewing allows you to see exactly how the document will appear when printed. If you have a WYSIWYG, previewing is unnecessary because the display screen always resembles the printed version. For word processors that are not WYSIWYGs, however, previewing is the next-best thing. If your word processor does not support previewing, you may be able to buy a separate program that allows you to preview documents.


primary cache

A memory cache built into the microprocessor.


primary storage

A somewhat dated term for main memory. Mass storage devices, such as disk drives and tapes, are sometimes called secondary storage.


print merge

Same as mail merge.


Print Screen key

Often abbreviated Prt Scr, the Print Screen key is a useful key supported on most PCs. In DOS, pressing the Print Screen key causes the computer to send whatever images and text are currently on the display screen to the printer. Some graphics applications, including Windows, use the Print Screen key to obtain screen captures.


print server

See under server.


print spooling

See under spooling.


printed circuit board

Sometimes abbreviated PCB, a thin, rectangular plate on which chips and other electronic components are placed. Computers consist of one or more boards, often called cards or adapters. Circuit boards fall into the following categories:

motherboard: The principal board that has connectors for attaching devices to the bus. Typically, the mother board contains the CPU, memory, and basic controllers for the system. On PCs, the motherboard is often called the system board.

expansion board: Any board that plugs into one of the computer's expansion slots. Expansion boards include controller boards, LAN cards, and video adapters.

daughterboard: Any board that attaches directly to an expansion board.

controller board: A special type of expansion board that contains a controller for a peripheral device. When you attach new devices, such as a disk drive or graphics monitor, to a computer, you often need to add a controller board.

Network Interface Card (NIC): An expansion board that enables a PC to be connected to a local-area network (LAN).

video adapter: An expansion board that contains a controller for a graphics monitor.


printer

A device that prints text or illustrations on paper. There are many different types of printers. In terms of the technology utilized, printers fall into the following categories:

daisy-wheel: Similar to a ball-head typewriter, this type of printer has a plastic or metal wheel on which the shape of each character stands out in relief. A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper. Daisy-wheel printers produce letter-quality print but cannot print graphics.

dot-matrix: Creates characters by striking pins against an ink ribbon. Each pin makes a dot, and combinations of dots form characters and illustrations.

ink-jet: Sprays ink at a sheet of paper. Ink-jet printers produce high-quality text and graphics.

laser: Uses the same technology as copy machines. Laser printers produce very high quality text and graphics.

LCD & LED: Similar to a laser printer, but uses liquid crystals or light-emitting diodes rather than a laser to produce an image on the drum.

line printer: Contains a chain of characters or pins that print an entire line at one time. Line printers are very fast, but produce low-quality print.

thermal printer: An inexpensive printer that works by pushing heated pins against heat-sensitive paper. Thermal printers are widely used in calculators and fax machines.

Printers are also classified by the following characteristics:

quality of type: The output produced by printers is said to be either letter quality (as good as a typewriter), near letter quality, or draft quality. Only daisy-wheel, ink-jet, and laser printers produce letter-quality type. Some dot-matrix printers claim letter-quality print, but if you look closely, you can see the difference.

speed: Measured in characters per second (cps) or pages per minute (ppm), the speed of printers varies widely. Daisy-wheel printers tend to be the slowest, printing about 30 cps. Line printers are fastest (up to 3,000 lines per minute). Dot-matrix printers can print up to 500 cps, and laser printers range from about 4 to 20 text pages per minute.

impact or non-impact: Impact printers include all printers that work by striking an ink ribbon. Daisy-wheel, dot-matrix, and line printers are impact printers. Non-impact printers include laser printers and ink-jet printers. The important difference between impact and non-impact printers is that impact printers are much noisier.

graphics: Some printers (daisy-wheel and line printers) can print only text. Other printers can print both text and graphics.

fonts: Some printers, notably dot-matrix printers, are limited to one or a few fonts. In contrast, laser and ink-jet printers are capable of printing an almost unlimited variety of fonts. Daisy-wheel printers can also print different fonts, but you need to change the daisy wheel, making it difficult to mix fonts in the same document.


Printer Control Language

See PCL.


printer driver

A program that controls a printer. Whenever you print a document, the printer driver takes over, feeding data to the printer with the correct control commands. Most modern operating systems come with printer drivers for the most common types of printers, but you must install them before you can use the printer.


printer engine

The main component of a printer that actually performs the printing. The printer engine determines how fast and at what resolution the printer can print. Although there are many manufacturers of printers, many use the same printer engines. The difference between printers using the same printer engine revolves around other features, such as paper handling abilities and the console.


printout

A printed version of text or data. Another term for printout is hard copy.


procedure

(1) Same as routine, subroutine, and function. A procedure is a section of a program that performs a specific task.

(2) An ordered set of tasks for performing some action.


process

(n) An executing program. The term is used loosely as a synonym of task.

(v) To perform some useful operations on data.


process colors

Refers to the CMYK color model used in offset printing.


processor

Short for microprocessor or CPU.


Prodigy

One of the largest online services, developed jointly by IBM and Sears. Prodigy is targeted particularly at home users, and sports an attractive graphical interface.


program

(n) An organized list of instructions that, when executed, causes the computer to behave in a predetermined manner. Without programs, computers are useless.

A program is like a recipe. It contains a list of ingredients (called variables) and a list of directions (called statements) that tell the computer what to do with the variables. The variables can represent numeric data, text, or graphical images.

There are many programming languages—C, C++, Pascal, BASIC, FORTRAN, COBOL, and LISP are just a few. These are all high-level languages. One can also write programs in low-level languages called assembly languages, although this is more difficult. Low-level languages are closer to the language used by a computer, while high-level languages are closer to human languages.

Eventually, every program must be translated into a machine language that the computer can understand. This translation is performed by compilers, interpreters, and assemblers.

When you buy software, you normally buy an executable version of a program. This means that the program is already in machine language—it has already been compiled and assembled and is ready to execute.

(v) To write programs.


programmable read-only memory

See PROM.


programmer

(1) An individual who writes programs.

(2) A device that writes a program onto a PROM chip.


programming language

A vocabulary and set of grammatical rules for instructing a computer to perform specific tasks. The term programming language usually refers to high-level languages, such as BASIC, C, C++, COBOL, FORTRAN, and Pascal. Each language has a unique set of keywords (words that it understands) and a special syntax for organizing program instructions.

High-level programming languages, while simple compared to human languages, are more complex than the languages the computer actually understands, called machine languages. Each different type of CPU has its own unique machine language.

Lying between machine languages and high-level languages are languages called assembly languages. Assembly languages are similar to machine languages, but they are much easier to program in because they allow a programmer to substitute names for numbers. Machine languages consist of numbers only.

Lying above high-level languages are languages called fourth-generation languages (usually abbreviated 4GL). 4GLs are far removed from machine languages and represent the class of computer languages closest to human languages.

Regardless of what language you use, eventually you need to convert your program into machine language so that the computer can understand it. There are two ways to do this:

•	compile the program

•	interpret the program

See compile and interpreter for more information about these two methods.

The question of which language is best is one that consumes a lot of time and energy among computer professionals. Every language has its strengths and weaknesses. For example, FORTRAN is a particularly good language for processing numerical data, but it does not lend itself very well to organizing large programs. Pascal is very good for writing well-structured and readable programs, but it is not as flexible as the C programming language. C++ embodies powerful object-oriented features, but it is complex and difficult to learn.

The choice of which language to use depends on the type of computer the program is to run on, what sort of program it is, and the expertise of the programmer.


PROM

Pronounced prom, an acronym for programmable read-only memory. A PROM is a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike main memory, PROMs retain their contents when the computer is turned off.

The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM.

An EPROM (erasable programmable read-only memory) is a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. An EEPROM is similar to a PROM, but requires only electricity to be erased.


prompt

A symbol on a display screen indicating that the computer is waiting for input. Once the computer has displayed a prompt, it waits for you to enter some information. Generally, it will wait forever, but some programs have built-in time-outs that cause the program to continue execution after it has waited a specified amount of time.


property

Characteristic of an object. In many programming languages, including Visual Basic, the term property is used to describe attributes associated with a data structure.


proportional font

A font in which different characters have different pitches (widths). Proportional fonts are also called proportional-pitch fonts. The opposite of a proportional font is a fixed-pitch font.


proportional pitch

Same as proportionally spaced. See under proportional spacing.


proportional spacing

Using different widths for different characters. In a proportionally spaced font, the letter I is narrower than the letter q and the letter m wider. This book uses a proportionally spaced font, as do most books, magazines, and newspapers.

The opposite of proportional spacing is monospacing. In a monospaced font, each character has the same width. Non-graphics display screens, display text in a monospaced font. Almost all printers, with the exception of line printers, are able to print with either proportionally spaced or monospaced fonts.


proprietary

Privately owned and controlled. In the computer industry, proprietary is the opposite of open. A proprietary design or technique is one that is owned by a company. It also implies that the company has not divulged specifications that would allow other companies to duplicate the product.

Increasingly, proprietary architectures are seen as a disadvantage. Consumers prefer open and standardized architectures, which allow them to mix and match products from different manufacturers.


protected mode

A type of memory utilization available on Intel 80286 and later model microprocessors. In protected mode, these processors provide the following features:

protection: Each program can be allocated a certain section of memory. Other programs cannot use this memory, so each program is protected from interference from other programs.

extended memory: Enables a single program to access more than 640K of memory.

virtual memory: Expands the address space to over 1GB.

multitasking: Enables the microprocessor to switch from one program to another so the computer can execute several programs at once.

Unfortunately, the DOS operating system is not designed to take advantage of these features. To run programs in protected mode, you need a more sophisticated operating system, such as OS/2, Windows, or UNIX.


protocol

An agreed-upon format for transmitting data between two devices. The protocol determines the following:

•	the type of error checking to be used

•	data compression method, if any

•	how the sending device will indicate that it has finished sending a message

•	how the receiving device will indicate that it has received a message

There are a variety of standard protocols from which programmers can choose. Each has particular advantages and disadvantages; for example, some are simpler than others, some are more reliable, and some are faster.

From a user's point of view, the only interesting aspect about protocols is that your computer or device must support the right ones if you want to communicate with other computers. The protocol can be implemented either in hardware or in software.


Prt Scr key

See Print Screen key.


public carrier

A government-regulated organization that provides telecommunications services to the public. This includes AT&T, MCI, and Western Union. Most public carriers provide electronic- mail services that enable you to send messages and documents over a telephone line to other computer users.


public-domain software

Refers to any program that is not copyrighted. Public-domain software is free and can be used without restrictions. The term public-domain software is often used incorrectly to include freeware, free software that is nevertheless copyrighted.


puck

A pointing device used with digitizing tablets. See under digitizing tablet.


pull-down menu

A menu of commands or options that appears when you select an item with a mouse. The item you select is generally at the top of the display screen, and the menu appears just below it, as if you had pulled it down.


punctuation

Like punctuation in human languages, punctuation in programming languages serves to separate words and phrases. But unlike human punctuation, which is often optional, computer punctuation is strictly required.


purge

To systematically and permanently remove old and unneeded data. The term purge is stronger than delete. It is often possible to regain deleted objects by undeleting them, but purged objects are gone forever.


push

In programming, to place a data item onto a stack. The opposite of push is pop, which means to remove an object from a stack.


push-button

A button in a dialog box. See under button.


QBE

See query by example.


QIC

The abbreviation for quarter-inch cartridge. QIC tapes are among the most popular tapes used for backing up personal computers. QIC tapes are divided into two general classes: full-size and minicartridge. The full-size cartridges are often referred to as DC 6000 cartridges, and minicartridges are called DC 2000 cartridges.

The QIC-40 and QIC-80 standards are sometimes referred to as floppy tape standards because they are designed to use a personal computer's existing floppy disk drive controller instead of requiring a customized controller.

The various QIC standards are controlled by a consortium of manufacturers called the Quarter-Inch Cartridge Drive Standards, Inc. The term QIC, therefore, is used to refer both to the type of tape and to the standards-producing organization.


quad-speed CD-ROM drive

A CD-ROM drive designed to run four times as fast as original models. Often denoted as 4X CD players, they provide data transfer rates of 600K per second and data access times as low as 125 milliseconds (ms).


quarter-inch cartridge

See QIC.


query

(n) A request for information from a database. There are three general methods for posing queries:

choosing parameters from a menu: In this method, the database system presents a list of parameters from which you can choose. This is perhaps the easiest way to pose a query because the menus guide you, but it is also the least flexible.

query by example (QBE): In this method, the system presents a blank record and lets you specify the fields and values that define the query.

query language: Many database systems require you to make requests for information in the form of a stylized query that must be written in a special query language. This is the most complex method because it forces you to learn a specialized language, but it is also the most powerful.

(v) To make a request for information from a database.


query by example

In database management systems, query by example (QBE) refers to a method of forming queries in which the database program displays a blank record with a space for each field. You can then enter conditions for each field that you want to be included in the query. For example, if you wanted to find all records where the AGE field is greater than 65, you would enter >65 in the AGE field blank.

QBE systems are considered easier to learn than formal query languages.


query language

A specialized language for requesting information from a database. For example, the query

SELECT ALL WHERE age > 30 AND name = “Smith”

requests all records in which the name-field is “Smith” and the Age field has a value greater than 30. The de facto standard for query languages is SQL.


queue

(v) To line up. In computer science, queuing refers to lining up jobs for a computer or device. For example, if you want to print a number of documents, the operating system (or a special print spooler) queues the documents by placing them in a special area called a print buffer or print queue. The printer then pulls the documents off the queue one at a time. Another term for this is print spooling.

The order in which a system executes jobs on a queue depends on the priority system being used. Most commonly, jobs are executed in the same order that they were placed on the queue, but in some schemes certain jobs are given higher priority.

(n) (1) A group of jobs waiting to be executed.

(2) In programming, a queue is a data structure in which elements are removed in the same order they were entered. This is often referred to as FIFO (first in, first out). In contrast, a stack is a data structure in which elements are removed in the reverse order from which they were entered. This is referred to as LIFO (last in, first out).


QuickDraw

The underlying graphics display system for Apple Macintosh computers. The QuickDraw system enables programs to create and manipulate graphical objects. Because all Macintosh programs use QuickDraw, they all share a common look.

There are several versions of QuickDraw that offer different color capabilities and other features. The newest, called QuickDraw GX, supports 16.7 million colors.

QuickDraw is currently used primarily for displaying images on monitors, but some printers use it as well.


QuickTime

A video and animation system developed by Apple Computer. QuickTime is built into the Macintosh operating system and is used by most Mac applications that include video or animation. PCs can also run files in QuickTime format, but they require a special QuickTime driver. On the PC side, QuickTime is competing with a number of other standards, including AVI, Indeo, and Cinepak.


quit

To exit a program in an orderly way. Compare with abort, which exits a program in an unorderly fashion.


QWERTY keyboard

Pronounced kwer-tee, refers to the arrangement of keys on a standard English computer keyboard or typewriter. The name derives from the first six characters on the top alphabetic line of the keyboard.

The arrangement of characters on a QWERTY keyboard was designed in 1868 by Christopher Sholes, the inventor of the typewriter. According to popular myth, Sholes arranged the keys in their odd fashion to prevent jamming on mechanical typewriters by separating commonly used letter combinations. However, there is no evidence to support this assertion, except that the arrangement does, in fact, inhibit fast typing.

With the emergence of ball-head electric typewriters and computer keyboards, on which jamming is not an issue, new keyboards designed for speed typing have been invented. The best-known is called a Dvorak keyboard. Despite their more rational designs, these new keyboards have not received wide acceptance.


radio buttons

In graphical user interfaces, groups of buttons, of which only one can be on at a time. When you select one button, all the others are automatically deselected. Compare with check box, which allows you to select any combination of options.


ragged

In text processing, ragged means not aligned along a margin. The opposite of ragged is flush or justified. For example, the following text has a ragged right margin:

This text has ragged right
margin because each
line ends at a different
spot.

Most word processors allow you to choose between ragged and justified margins.


RAM

Pronounced ramm, acronym for random access memory, a type of computer memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes. RAM is the most common type of memory found in computers and other devices, such as printers.

There are two basic types of RAM:

•	dynamic RAM (DRAM)

•	static RAM (SRAM)

The two types differ in the technology they use to hold data, dynamic RAM being the more common type. Dynamic RAM needs to be refreshed thousands of times per second. Static RAM needs to be refreshed less often, which makes it faster; but it is also more expensive than dynamic RAM. Both types of RAM are volatile, meaning that they lose their contents when the power is turned off.

In common usage, the term RAM is synonymous with main memory, the memory available to programs. For example, a computer with 8M RAM has approximately 8 million bytes of memory that programs can use. In contrast, ROM (read-only memory) refers to special memory used to store programs that boot the computer and perform diagnostics. Most personal computers have a small amount of ROM (a few thousand bytes). In fact, both types of memory (ROM and RAM) allow random access. To be precise, therefore, RAM should be referred to as read/write RAM and ROM as read-only RAM.


RAM cache

(1) Same as processor cache.

(2) On Apple Macintosh computers, the term RAM cache refers to a disk cache.


RAM disk

Refers to RAM that has been configured to simulate a disk drive. You can access files on a RAM disk as you would access files on a real disk. RAM disks, however, are approximately a thousand times faster than hard disk drives. They are particularly useful, therefore, for applications that require frequent disk .

Because they are made of normal RAM, RAM disks lose their contents once the computer is turned off. To use a RAM disk, therefore, you need to copy files from a real hard disk at the beginning of the session and then copy the files back to the hard disk before you turn the computer off. Note that if there is a power failure, you will lose whatever data is on the RAM disk. (Some RAM disks come with a battery backup to make them more stable.)


RAM resident

Same as memory resident.


random access

Refers to the ability to access data at random. The opposite of random access is sequential access. To go from point A to point Z in a sequential-access system, you must pass through all intervening points. In a random-access system, you can jump directly to point Z. Disks are random access media, whereas tapes are sequential access media.

The terms random access and sequential access are often used to describe data files. A random-access data file enables you to read or write information anywhere in the file. In a sequential-access file, you can only read and write information sequentially, starting from the beginning of the file.

Both types of files have advantages and disadvantages. If you are always accessing information in the same order, a sequential-access file is faster. If you tend to access information randomly, random access is better.

Random access is sometimes called direct access.


random-access memory

See RAM.


range

In spreadsheet applications, one or more contiguous cells. For example, a range could be an entire row or column, or multiple rows or columns. The only restrictions on ranges is that all the cells of the range must be contiguous and the entire range must be rectangular in shape; that is, you cannot have a range consisting of three cells in one column and four cells in the next.

Once you have defined a range, you can perform operations on it. This is a powerful feature because it allows you to manipulate a set of cells with one expression.


raster graphics

See under bit-mapped graphics.


raster image processor (RIP)

A hardware-software combination that converts a vector image into a bit-mapped image. All PostScript printers contain a RIP that converts the PostScript commands into bit-mapped pages that the printer can output.


raw data

Information that has not been organized, formatted, or analyzed.


ray tracing

In computer graphics, an advanced technique for adding realism to an image by including variations in shade, color intensity, and shadows that would be produced by having one or more light sources. Ray tracing software works by simulating the path of a single light ray as it would be absorbed or reflected by various objects in the image. To work properly, the artist must specify parameters of the light source (intensity, color, etc.) as well as all the objects (how reflective or absorbent the materials are).

Ray tracing requires enormous computational resources, and is supported by only the most advanced graphics systems.


RDBMS

Short for relational database management system and pronounced as separate letters.


read

(v) To copy data from a storage medium, such as a disk, to main memory, where it can be utilized by a program.

(n) The act of reading. For example, a fast disk drive performs 100 reads per second.


read-only

Capable of being displayed, but not modified or deleted. All operating systems allow you to protect objects (disks, files, directories) with a read-only attribute that prevents other users from modifying the object.


read-only memory

See ROM.


read/write

Capable of being displayed (read) and modified (written to). Most objects (disks, files, directories) are read/write, but operating systems also allow you to protect objects with a read-only attribute that prevents other users from modifying the object.


read/write head

See head.


readme file

A small text file that comes with many software packages and contains information not included in the official documentation. Typically, readme files contain late-breaking information that could not be included in the printed documentation.


real address

Same as absolute address.


real mode

An execution mode supported by the Intel 80286 and later processors. In real mode, these processors imitate the Intel 8088 and 8086 microprocessors, although they run much faster. The other mode available is called protected mode. In protected mode, programs can access extended memory and virtual memory. Protected mode also supports multitasking. The 80386 and later microprocessors support a third mode called virtual 8086 mode. In virtual mode, these microprocessors can run several real-mode programs at once.

The DOS operating system was not designed to take advantage of protected mode, so it always executes programs in real mode.


real time

Occurring immediately. The term is used to describe a number of different computer features. For example, real-time operating systems are systems that respond to input immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react.

Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In graphics animation, for example, a real-time program would display objects moving across the screen at the same speed that they would actually move.


real-time clock

A clock that keeps track of the time even when the computer is turned off. Real-time clocks run on a special battery that is not connected to the normal power supply. In contrast, clocks that are not real-time do not function when the computer is off.

Do not confuse a computer's real-time clock with its CPU clock. The CPU clock regulates the execution of instructions.


reboot

To restart a computer. On a PC, you can reboot by pressing the Alt, Control and Delete keys simultaneously. This is called a warm boot. You can also perform a cold boot by turning the computer off and then on again.

On Macs, you reboot by selecting the “Restart” option from the Special menu.


recalculate

In spreadsheet programs, recalculation refers to computing the values of cells in a spreadsheet. Recalculation is necessary whenever you change a formula or enter new data into one or more cells. Depending on the size and complexity of your spreadsheet, recalculation can be a time-consuming process. One criterion for evaluating spreadsheet programs, therefore, is how fast they recalculate.

To make recalculation faster, many spreadsheet programs support minimal recalculation (also called optimal recalculation), in which the program calculates only the values of cells that will change. In addition, some spreadsheets support background recalculation, which allows you to perform other operations while a recalculation is in progress.


record

(1) In database management systems, a complete set of information. Records are composed of fields, each of which contains one item of information. A set of records constitutes a file. For example, a personnel file might contain records that have three fields: a name field, an address field, and a phone number field.

(2) Some programming languages allow you to define a special data structure called a record. Generally, a record is a combination of other data objects. For example, a record might contain three integers, a floating-point number, and a character string.


record locking

See under lock.


recursion

A programming method in which a routine calls itself. Recursion is an extremely powerful concept, but it can strain a computer’s memory resources. Some programming languages, such as LISP and Prolog, are specifically designed to use recursive methods.


red-green-blue monitor

See RGB monitor.


redirection

In operating system shells, redirection refers to directing input and output to files and devices other than the default I/O devices. By default, input generally comes from the keyboard or mouse, and output goes to the display monitor. With a redirection operator, you can override these defaults so that a command or program takes input from some other device and sends output to a different device.

In DOS and UNIX systems, the redirection operators are < for input and > for output. For example, the DOS command

sort < c:\list > c:\sorted

takes input from a file called list, sorts it, and sends output to a file called sorted.


redlining

In word processing, redlining refers to marking text that has been edited. Typically, redlining is used when two or more people are working on a document together; each individual can redline the text he or she has added or edited. The redlined text will then appear in a special color (or as bold) so that others can see the changes that have been made.


reduced instruction set computer

See RISC.


refresh

To recharge a device with power or information. For example, dynamic RAM needs to be refreshed thousands of times per second or it will lose the data stored in it.

Similarly, display monitors must be refreshed many times per second. The refresh rate for a monitor is measured in hertz (Hz) and is also called the vertical frequency or vertical refresh rate. The old standard for monitor refresh rates was 60Hz, but a new standard developed by VESA sets the refresh rate at 75Hz for VGA and SVGA monitors. The faster the refresh rate, the less the monitor flickers.


register

(n) A storage area within the CPU. All data must be represented in a register before it can be processed. For example, if two numbers are to be multiplied, both numbers must be in registers, and the result is also placed in a register. (The register can contain the address of a memory location where data is stored rather than the actual data itself.)

The number of registers that a CPU has and the size of each (number of bits) help determine the power and speed of a CPU. For example a 32-bit CPU is one in which each register is 32 bits wide. Therefore, each CPU instruction can manipulate 32 bits of data.

Usually, the movement of data in and out of registers is completely transparent to users, and even to programmers. Only assembly language programs can manipulate registers. In high-level languages, the compiler is responsible for translating high-level operations into low-level operations that access registers.

(v) To notify a manufacturer that you have purchased its product. Registering a product is often a prerequisite to receiving customer support, and it is one of the ways that software producers control software piracy.


relational database

A type of database that stores data in the form of a table. Relational databases are powerful because they require few assumptions about how data is related or how it will be extracted from the database. As a result, the same database can be viewed in many different ways.

Another feature of relational systems is that a single database can be spread across several tables. This differs from flat-file databases, in which each database is self-contained in a single table.

Almost all full-scale database systems for personal computers use a relational database. Small database systems, however, use other designs that provide less flexibility in posing queries.


relational expression

See under relational operator.


relational operator

An operator that compares two values.

For example, the expression

x < 5

means x is less than 5. This expression will have a value of TRUE if the variable x is less than 5; otherwise the value of the expression will be FALSE.

Relational operators are sometimes called comparison operators. Expressions that contain relational operators are called relational expressions.


relative address

An address specified by indicating its distance from another address, called the base address. For example, a relative address might be B+15, B being the base address and 15 the distance (called the offset).

There are two types of addressing: relative addressing and absolute addressing. In absolute addressing, you specify the actual address (called the absolute address) of a memory location.

Relative and absolute addressing are used in a variety of circumstances. In programming, you can use either mode to identify locations in main memory or on mass storage devices. In spreadsheet applications, you can use either mode to designate a particular cell.


relative cell reference

In spreadsheet applications, a reference to a cell or group of cells by indicating how far away it is from some other cell. For example, in Lotus 1-2-3 and many other spreadsheet programs, the cell reference “C2” is relative. Initially it points to the cell in the third column and second row, but it does this by specifying how far away this cell is from some other cell. For example, if you insert this reference in cell A1, the program will translate it to “2 columns right and 1 row down”. If you then copy the reference to cell B4, it will now point to cell D5.

In contrast, an absolute cell reference always points to the same cell, no matter where the reference appears.


remote

In networks, remote refers to files, devices, and other resources that are not connected directly to your workstation. Resources at your workstation are considered local.


remote control

Refers to a program's ability to access a computer system from a remote location. Remote-control programs for PCs enable you to access data stored on your home system even when you are traveling.


removable cartridge

Same as removable hard disk.


removable hard disk

A type of disk drive system in which hard disks are enclosed in plastic or metal cartridges so that they can be removed like floppy disks. Removable disk drives combine the best aspects of hard and floppy disks. They are as fast as hard disks and have the portability of floppy disks. The storage capacity of a typical removable hard disk can range from 60MB (megabytes) to 250MB, much more than the capacity of floppy disks.


rendering

Refers to the process of adding realism to a computer graphics by adding three-dimensional qualities such as shadows and variations in color and shade. One technique for rendering graphics is called ray tracing.


repaginate

To recalculate page breaks. Word processing and desktop publishing systems decide where to end one page and begin the next based on a set of parameters including the page size, margin size, and widow and orphan settings. Most systems automatically repaginate whenever you modify a document. However, repagination can be time-consuming, so some systems allow you temporarily turn off automatic repagination until you‘re ready.


replace

To insert a new object in place of an existing object. The term is used most often in connection with search and replace operations, in which you search for one word or phrase and replace all occurrences with a new word or phrase.


report

A formatted and organized presentation of data. Most database management systems include a report writer that enables you to design and generate reports.


report generator

Same as report writer.


report writer

A program, usually part of a database management system, that extracts information from one or more files and presents the information in a specified format. Most report writers allow you to select records that meet certain conditions and to display selected fields in rows and columns. You can also format data into pie charts, bar charts, and other diagrams. Once you have created a format for a report, you can save the format specifications in a file and continue reusing it for new data.

The report writer is one of the most important components of a database management system because it determines how much flexibility you have in outputting data.


reserved word

A special word reserved by a programming language or by a program. You are not allowed to use reserved words as variable names. For example, in BASIC and COBOL, the word IF is reserved because it has a special meaning.

Reserved words are sometimes called keywords.


reset button

A button or switch on many computers that allows you to reset the computer. When you press the reset button, the computer will enter its start-up procedure as if you had turned the power off and then on again. Generally, you would use the reset button only when a program error has caused your computer to hang.

Note that on PCs, pressing the reset button is somewhat different from performing a warm reboot by pressing the Ctrl+Alt+Del reboot keys. When you perform a warm reboot, the system does not repeat the initial start-up stages during which memory is checked.


resident

(1) See memory resident.

(2) See resident font.


resident font

Also called an internal font or built-in font, a resident font is a font built into the hardware of a printer. All dot-matrix and laser printers come with one or more resident fonts. You can add additional fonts by inserting font cartridges or downloading soft fonts.


resize

See under size.


resolution

Refers to the sharpness and clarity of an image. The term is most often used to describe monitors, printers, and bit-mapped graphic images. In the case of dot-matrix and laser printers, the resolution indicates the number of dots per inch. For example, a 300-dpi (dots per inch) printer is one that is capable of printing 300 distinct dots in a line 1 inch long. This means it can print 90,000 dots per square inch.

For graphics monitors, the resolution signifies the number of dots (pixels) on the entire screen. For example, a 640-by-480 pixel screen is capable of displaying 640 distinct dots on each of 480 lines, or about 300,000 pixels. This translates into different dpi measurements depending on the size of the screen. For example, a 15-inch VGA monitor (640x480) displays about 50 dots per inch.

Printers, monitors, scanners, and other I/O devices are often classified as high resolution, medium resolution, or low resolution. The actual resolution ranges for each of these grades is constantly shifting as the technology improves.


resolution enhancement

A collection of techniques used in many laser printers to enable the printer to print at a higher resolution than normal. Most laser printers have printer engines that print at either 300 dpi (dots per inch) or 600 dpi. Using clever algorithms that recognize curved lines, a printer with resolution enhancement can produce output whose resolution appears to be much higher than the print engine’s rated resolution. This is why many printer manufacturers characterize their printers with two resolution ratings: the engine resolution and the effective resolution.

A common resolution enhancement technique is to vary the size of the dots.


resource

(1) Generally, any item that can be used. Devices such as printers and disk drives are resources, as is memory.

(2) In many operating systems, including Microsoft Windows and the Macintosh operating system, the term resource refers specifically to data or routines that are available to programs.


restore

In graphical user interfaces, to restore means to return a window to its original size.


return

A return is a special code that causes a word processor or other application to advance to the beginning of the next line. A soft return is a return that the application inserts automatically when you reach the end of a line. A hard return is a return that you explicitly enter by pressing the Return or Enter key.


Return key

Almost all computer keyboards have a key marked Return or Enter; the two names are synonymous. The Return key moves the cursor (or insertion point) to the beginning of the next line. But more important, it returns control to whatever program is currently running. After a program requests information from you (by displaying a prompt), it will usually not respond to your input until you have pressed the Return key. This allows you to correct typing mistakes or to reconsider your entry before it is too late. In many applications, pressing the Return key moves the cursor to the next field.

In word-processing programs, pressing the Return key inserts a hard return into a document.

In technical documentation, the Return key is sometimes signified by a [image].


reverse engineering

The process of recreating a design by analyzing a final product. Reverse engineering is common in both hardware and software. Several companies have succeeded in producing  Intel-compatible microprocessors through reverse engineering. Whether reverse engineering is legal or not depends on who you ask. The courts have not yet made a definitive ruling.


reverse video

A display method that causes a portion of the display to appear like a negative of the regular display. If the display screen normally displays light images against a dark background, putting it in reverse video mode will cause it to display dark images against a light background.

Many programs use reverse video to highlight items, such as selected text or menu options. Also, some systems allow you to change the mode for all displays, so you can choose the display that is most comfortable for you. Some people prefer dark images on a light background, while others prefer light images on a dark background.


RGB monitor

Short for red, green, blue monitor, a monitor that requires separate signals for each of the three colors. This differs from color televisions, for example, which use composite video signals, in which all the colors are mixed together. All color computer monitors are RGB monitors.

An RGB monitor consists of a vacuum tube with three electron guns—one each for red, green, and blue—at one end and the screen at the other end. The three electron guns fire electrons at the screen, which contains a phosphorous coating. When the phosphors are excited by the electron beams, they glow. Depending on which beam excites them, they glow either red, green, or blue. Ideally, the three beams should converge for each point on the screen so that each pixel is a combination of the three colors.


rich text format (RTF)

A standard developed by Microsoft Corporation for specifying formatting of documents. RTF files are actually ASCII files with special commands to indicate formatting information, such as fonts and margins. Microsoft has tried to make RTF the universal document formatting language, but up till now it has not been successful. Other document formatting languages that are gaining ground are the Hypertext Markup Language (HTML), which is used to define documents on the World Wide Web, and the Standard Generalized Markup Language (SGML), which is a more robust version of HTML.


right justify

See under justify.


ring network

A local-area network (LAN) whose topology is a ring. That is, all of the nodes are connected in a closed loop. Messages travel around the ring, with each node reading those messages addressed to it. One of the advantages of ring networks is that they can span larger distances than other types of networks, such as bus networks, because each node regenerates messages as they pass through it.


RIP

Pronounced rip, acronym for raster image processor. See raster image processor (RIP).


RISC

Pronounced risk, acronym for reduced instruction set computer, a type of microprocessor that recognizes a relatively limited number of instructions. Until the mid-1980s, the tendency among computer manufacturers was to build increasingly complex CPUs that had ever-larger sets of instructions. At that time, however, a number of computer manufacturers decided to reverse this trend by building CPUs capable of executing only a very limited set of instructions. One advantage of reduced instruction set computers is that they can execute their instructions very fast because the instructions are so simple. Another, perhaps more important advantage, is that RISC chips require fewer transistors, which makes them cheaper to design and produce. Since the emergence of RISC computers, conventional computers have been referred to as CISCs (complex instruction set computers).

There is still considerable controversy among experts about the ultimate value of RISC architectures. Its proponents argue that RISC machines are both cheaper and faster, and are therefore the machines of the future. Skeptics note that by making the hardware simpler, RISC architectures put a greater burden on the software. They argue that this is not worth the trouble because conventional microprocessors are becoming increasingly fast and cheap anyway.

To some extent, the argument is becoming moot because CISC and RISC implementations are becoming more and more alike. Many of today's RISC chips support as many instructions as yesterday's CISC chips. And today’s CISC chips use many techniques formerly associated with RISC chips.


RLL

Abbreviation of run length limited, an encoding scheme used to store data on some PC hard disks. Although RLL produces fast data access times and increases a disk's storage capacity, it is not as prevalent as another encoding scheme called MFM (modified frequency modulation).

Technically, any disk drive can use either encoding method. The one used depends on the disk controller.


robotics

The field of computer science and engineering concerned with creating robots, devices that can move and react to sensory input. Robotics is one branch of artificial intelligence.

Robots are now widely used in factories to perform high-precision jobs such as welding and riveting. They are also used in special situations that would be dangerous for humans—for example, in cleaning toxic wastes or defusing bombs.

Although great advances have been made in the field of robotics during the last decade, robots are still not very useful in everyday life, as they are too clumsy to perform ordinary household chores.


ROM

Pronounced rahm, acronym for read-only memory, computer memory on which data has been prerecorded. Once data has been written onto a ROM chip, it cannot be removed and can only be read.

Unlike main memory (RAM), ROM retains its contents even when the computer is turned off. ROM is referred to as being nonvolatile, whereas RAM is volatile.

Most personal computers contain a small amount of ROM that stores critical programs such as the program that boots the computer. In addition, ROMs are used extensively in calculators and peripheral devices such as laser printers, whose fonts are often stored in ROMs.

A variation of a ROM is a PROM (programmable read-only memory). PROMs are manufactured as blank chips on which data can be written with a special device called a PROM programmer.


ROM-BIOS

See BIOS.


roman

In typography, roman refers to fonts with characters that are straight up and down rather than slanted. A font designed with characters slanted to the right is italic.


root directory

The top directory in a file system. The root directory is provided by the operating system and has a special name; for example, in DOS systems the root directory is called \. The root directory is sometimes referred to simply as the root.


router

A device that connects two LANs of the same type. Routers are similar to bridges, but provide additional functionality, such as the ability to filter messages and forward them to different places based on various criteria.


routine

A section of a program that performs a particular task. Programs consist of modules, each of which contains one or more routines. The term routine is synonymous with procedure, function, and subroutine.


RS-232C

A standard interface (RS stands for recommended standard) approved by the Electronics Industry Association (EIA) for connecting serial devices. Almost all modems conform to the RS-232C standard and most personal computers have an RS-232C port for connecting a modem or other device. In addition to modems, many display screens, mice, and serial printers are designed to connect to a RS-232C port.

The RS-232C standard supports two types of connectors—a 25-pin D-type connector (DB-25) and a 9-pin D-type connector (DB-9). The type of serial communications used by PCs requires only 9 pins so either type of connector will work equally well.

Although RS-232C is still the most common standard for serial communication, the EIA has recently defined successors to RS-232C called RS-422 and RS-423. The new standards are backward compatible so that RS-232 devices can connect to an RS-422 port.

In 1987, the EIA upgraded and changed the named of RS-232C. The new name is EIA-232D, but the standard is generally still referred to by its old name.


RS-422 and RS-423

Standard interfaces approved by the Electronics Industry Association (EIA) for connecting serial devices. The RS-422 and RS-423 standards are designed to replace the older RS-232C standard because they support higher data rates and greater immunity to electrical interference. All Apple Macintosh computers contain an RS-422 port that can also be used for RS-232C communication.


RTF

See rich text format (RTF).


rule

(1) In word processing and desktop publishing, a straight line that separates columns of text or illustrations.

(2) In expert systems, a conditional statement that tells the system how to react to a particular situation.


ruler

In word processing, a line running across the display screen. It measures the page layout in points, picas, inches, or centimeters. It is sometimes called the ruler line and is particularly useful for setting margins and tabs. Sophisticated desktop publishing systems and page layout programs sometimes support movable rulers that you can move around the display screen to measure particular items of text or graphics.


run

(1) To execute a program.

(2) To operate. For example, a device that is running is one that is turned on and operating properly.


run length limited

See RLL.


running head

See under header.


runtime error

An error that occurs during the execution of a program. In contrast, compile-time errors occur while a program is being compiled. Runtime errors indicate bugs in the program or problems that the designers had anticipated but could do nothing about. For example, running out of memory will often cause a runtime error.

Note that runtime errors differ from bombs or crashes in that you can often recover gracefully from a runtime error.


runtime version

A limited version of one program that enables you to run another program. To run a program written in Visual BASIC, for example, you need the runtime version of Visual Basic. This allows you to run Visual Basic programs but not to develop them yourself. Many other development applications, particularly database applications, require a runtime version to execute.

Software companies have different approaches to runtime versions. Some allow you to distribute the runtime version freely, while others require that you pay a license fee.


sampling

A technique used to capture continuous phenomena, whereby periodic snapshots are taken. If the sampling rate is fast enough, the human sensory organs cannot discern the gaps between each snapshot when they are played back. This is the principle behind motion pictures.

Sampling is the key technique used to digitize analog information. For example, music CDs are produced by sampling live sound at frequent intervals and then digitizing each sample. The term sampling is also used to describe a similar process in digital photography.


sans serif

Pronounced san-serr-if, refers to a category of typefaces that do not use serifs, small lines at the ends of characters. Popular sans serif fonts include Helvetica, Avant Garde, Arial, and Geneva. Serif fonts include Times Roman, Courier, New Century Schoolbook, and Palatino.

According to most studies, sans serif fonts are more difficult to read. For this reason, they are used most often for short text components such as headlines or captions.


save

To copy data from a temporary area to a more permanent storage medium. When you edit a file with a word processor, for example, the word processor copies the entire file, or portions of the file, into an area of main memory called a buffer. Any changes you make to the file are made to the copy in the buffer, not to the real file on the disk. The buffer is temporary—as soon as you exit the program or turn off the computer, the buffer disappears. To record your modifications to the file on the disk, you must save the file. When you do this, the word processor copies the contents of the buffer back to the file on the disk, replacing the previous version of the file.

Because computers can break down at any moment, it is a good idea to save your files periodically. Otherwise, you will lose all the work you have done during an editing session. Many applications automatically save files at regular intervals, which you can specify. These intermediate saves are sometimes called snapshots.


scalable font

A font represented in an object-oriented graphics language such as PostScript or TrueType. Such fonts are called scalable because the representation of the font defines the shape of each character (the typeface) but not the size. Given a typeface definition, a scalable-font system can produce characters at any size (or scale).

Aside from offering innumerable sizes of each font, scalable fonts have an added advantage in that they make the most of an output device's resolution. The more resolution a printer or monitor has, the better a scalable font will look.

Scalable fonts are often called outline fonts because the most common method of representing scalable fonts is to define the outline of each character. Scalable fonts are also called object-oriented fonts or vector fonts.


scale

To change the size of an object while maintaining its shape. Most graphics software, particularly vector-based packages, allow you to scale objects freely.


scan

To digitize an image by passing it through an optical scanner. See under optical scanner.


scanner

See optical scanner.


scatter diagram

A type of diagram used to show the relationship between data items that have two numeric properties. One property is represented along the x-axis and the other along the y-axis. Each item is then represented by a single point.

Scatter diagrams are used frequently by computer publications to compare categories of hardware and software products. One axis represents price, while the other represents performance. Typically, all compared products fall near an imaginary diagonal line—that is, performance and price rise together. However, the scatter diagram makes it easy to see items that do not fall near this line, items that are expensive but offer poor performance or items that are inexpensive but provide good performance.


scheduler

(1) A software product designed to help a group of colleagues schedule meetings and other appointments. The scheduler program allows members of a group to view each others' calendars so that they can choose a convenient time. Once a time has been selected, the scheduler can automatically send out reminders through e-mail and can even reserve resources such as conference rooms and overhead projectors.

(2) In operating systems, a scheduler is a program that coordinates the use of shared resources, such as a printer.


scientific notation

A format for representing real (floating-point) numbers. Instead of writing the full number, scientific notation represents values as a number between 1 and 10 multiplied by 10 to some power. The 10 is often replaced by an uppercase or lowercase E.

Scientific notation is much simpler for very large and very small numbers, such as the second and fourth examples. Most programming languages, and many numeric applications, allow you to enter and display numbers using scientific notation.


scissoring

Same as clipping. See under clip.


Scrapbook

In Macintosh environments, a desk accessory (DA) that enables you to store objects for future use. The Scrapbook is similar to the clipboard, but it allows more than one item to be stored in it at once. Also, it retains its contents when the computer is turned off.


screen

(1) Short for display screen.

(2) In offset printing, a mesh used to create halftones. See under halftone.


screen capture

Refers to the act of copying what is currently displayed on a screen to a file or printer. If the system is in graphics mode, the screen capture will result in a graphics file containing a bit map of the image. If the system is in text mode, the screen capture will normally load a file with ASCII codes.


screen dump

Same as screen capture.


screen flicker

The phenomenon whereby a display screen appears to flicker. Screen flicker results from a variety of factors, the most important of which is the monitor's refresh rate, the speed with which the screen is redrawn. If the refresh rate is too slow, the screen will appear to glimmer. Another factor that affects screen flicker is the persistence of the screen phosphors. Low-persistence phosphors fade more quickly than high-persistence monitors, making screen flicker more likely. Screen flicker can also be affected by lighting. Finally, screen flicker is a subjective perception that affects people differently. Some people perceive screen flicker where others do not.


screen font

A font designed especially for a display screen. Typically, display fonts are bit-mapped, and must be specially designed to compensate for the relatively low resolution of display screens.


screen saver

A small program that takes over the display screen if there are no keystrokes or mouse movements for a specified duration. Screen savers were originally developed to prevent ghosting, the permanent etching of a pattern on a display screen. For older monochrome monitors, ghosting often occurred if the same pattern was displayed on a display screen for a long period of time. Screen savers would prevent this by either blanking out the screen entirely or by displaying a constantly moving image.

Modern display screens do not suffer so much from this problem. Today, therefore, screen savers are mostly an adornment, a way to liven up the computer. Many screen savers provide another benefit, hiding a user’s work from would-be snoopers. These screen savers fill the display with an image or animation until the user enters a password.


screen shot

Same as screen capture.


script

Another term for macro or batch file, a script is a list of commands that can be executed without user interaction. A script language is a simple programming language with which you can write scripts.

Apple Computer uses the term script to refer to programs written in its HyperCard language.


scroll

To view consecutive lines of data on the display screen. The term scroll means that once the screen is full, each new line appears at the edge of the screen and all other lines move over one position. For example, when you scroll down, each new line appears at the bottom of the screen and all the other lines move up one row, so that the top line disappears.

The term vertical scrolling refers to the ability to scroll up or down. Horizontal scrolling means that the image moves sideways.

In theory, the display should move smoothly, as if it were a piece of paper being moved up, down, or sideways. In practice, however, scrolling is not always so smooth.

The scrolling method of viewing documents does not recognize page boundaries. One advantage to scrolling, therefore, is that you can look at the end of one page and the beginning of the next page at the same time.

Another method of viewing data is called paging, whereby an entire page is displayed at once. Each subsequent page replaces the previous page on the screen.


scroll bar

A bar that appears on the side or bottom of a window to control which part of a list or document is currently in the window's frame. The scroll bar makes it easy to move to any part of a file.

Typically, a scroll bar has arrows at either end, a gray or colored area in the middle, and a scroll box (or elevator) that moves from one end to the other to reflect your position in the document. Clicking on the arrows causes the document to scroll in the indicated direction. You can also quickly move to any part of a document by dragging the scroll box to the corresponding part of the scroll bar.

Many windowing systems support both horizontal and vertical scroll bars.


scroll box

See under scroll bar.


Scroll Lock key

A key on PC and enhanced Macintosh keyboards that controls the way the cursor control keys work for some programs. Many applications ignore the Scroll Lock setting.


SCSI

Abbreviation of small computer system interface. Pronounced scuzzy, SCSI is a parallel interface standard used by Apple Macintosh computers, some PCs, and many UNIX systems for attaching peripheral devices to computers. All Apple Macintosh computers starting with the Macintosh Plus come with a SCSI port for attaching devices such as disk drives and printers.

SCSI interfaces provide for faster data transmission rates (up to 4 megabytes per second) than standard serial and parallel ports. In addition, you can attach up to seven devices to a single SCSI port, so that SCSI is really an I/O bus rather than simply an interface.

Although SCSI is an ANSI standard, there are many variations of it, so two SCSI interfaces may be incompatible. For example, SCSI supports several types of connectors.

While SCSI is the only standard interface for Macintoshes, PCs support a variety of interfaces in addition to SCSI. These include IDE, enhanced IDE and ESDI for mass storage devices, and Centronics for printers. You can, however, attach SCSI devices to a PC by inserting a SCSI board in one of the expansion slots. Many high-end new PCs come with SCSI built in. Note, however, that the lack of a single SCSI standard means that some devices may not work with some SCSI boards.

A new ANSI standard, called SCSI-2, widens the data bus from 8 to either 16 or 32 bits and provides a burst mode for transferring data to and from disk drives. SCSI-2 can support data rates as fast as 10 megabytes per second (Mbps). SCSI-2 is sometimes called Fast SCSI, Wide SCSI, Fast/Wide SCSI or Fast SCSI-2.

Yet a third SCSI variation, known as SCSI-3, is expected to be ratified by ANSI in 1996. SCSI-3, also known as UltraSCSI, will support data transfer rates as fast as 40 Mbps.


search and replace

A feature supported by most word processors that lets you replace a character string (a series of characters) with another string wherever the first string appears in the document. Most word processors have two search and replace modes. In the first mode, the word processor automatically makes all the replacements in the file. In the second mode, the word processor requires you to approve each replacement. This is safer because you may not want to make the change everywhere.

Search and replace is sometimes called find and replace.


secondary cache

Cache memory that is external to the microprocessor. In general, secondary cache memory, also called L2 cache, resides on a separate chip from the microprocessor chip. The Pentium Pro, however, has a secondar cache on the same chip as the microprocessor.


secondary storage

Same as mass storage.


sector

The smallest unit that can be accessed on a disk. When you format a disk, the operating system divides it into tracks and sectors. The tracks are concentric circles around the disk and the sectors are segments within each circle. For example, a formatted disk might have 40 tracks, with each track divided into 10 sectors. The operating system and disk drive keep tabs on where information is stored on the disk by noting its track and sector number.

Generally, every track has the same number of sectors, but some high-capacity hard disk drives use a technique called zoned-bit recording in which tracks on the outside of the disk contain more sectors than those on the inside.

A sector that cannot be used due to a physical flaw on the disk is called a bad sector.


security

Refers to techniques for ensuring that data stored in a computer cannot be read or compromised. Most security measures involve data encryption and passwords. Data encryption is the translation of data into a form that is unintelligible without a deciphering mechanism. A password is a secret word or phrase that gives a user access to a particular program or system.


seek time

Refers to the time a program or device takes to locate a particular piece of data. For disk drives, the terms seek time and access time are often used interchangeably.


segment

(1) In virtual memory systems, a segment is a variable-sized portion of data that is swapped in and out of main memory. Contrast with page, which is a fixed-sized portion of data.

(2) A piece of a polyline. See under polyline.


select

To choose an object so that you can manipulate it in some way. In graphical user interfaces, you usually need to select an object—an icon, file, folder, and so on—before you can do anything with it. To select an object, you move the pointer to the object and click a mouse button. In many applications, you can select blocks of text by positioning the pointer at an end-point of the block and then dragging the pointer over the block.


semantics

In linguistics, the study of meanings. In computer science, the term is frequently used to differentiate the meaning of an instruction from its format. The format, which covers the spelling of language components and the rules controlling how components are combined, is called the language's syntax. For example, if you misspell a command, it is a syntax error. If, on the other hand, you enter a legal command that does not make any sense in the current context, it is a semantic error.


semiconductor

A material that is neither a good conductor of electricity (like copper) nor a good insulator (like rubber). The most common semiconductor materials are silicon and geranium. Computer chips, both for CPU and memory, are composed of semiconductor materials. Semiconductors make it possible to miniaturize electronic components. Not only does miniaturization mean that the components take up less space, it also means that they are faster and require less energy.


sequential access

Refers to reading or writing data records in sequential order, that is, one record after the other. To read record 10, for example, you would first need to read records 1 through 9. This differs from random access, in which you can read and write records in any order.

Some programming languages and operating systems distinguish between sequential-access data files and random-access data files, allowing you to choose between the two types. Sequential-access files are faster if you always access records in the same order. Random-access files are faster if you need to read or write records in a random order.

Devices can also be classified as sequential access or random access. For example, a tape drive is a sequential-access device because to get to point q on the tape, the drive needs to pass through points a through p. A disk drive, on the other hand, is a random-access device because the drive can access any point on the disk without passing through all intervening points.


serial

One by one. Serial data transfer refers to transmitting data one bit at a time. The opposite of serial is parallel, in which several bits are transmitted concurrently.


serial interface

Same as serial port.


Serial Line Internet Protocol

See SLIP.


serial mouse

A mouse that connects to a computer via a serial port. The other type of mouse is a bus mouse, which attaches to a computer via an expansion board. Serial mice are easier to install, but they require an unused serial port.


serial port

A port, or interface, that can be used for serial communication, in which only 1 bit is transmitted at a time.

Most serial ports on personal computers conform to the RS-232C or RS-422 standards. A serial port is a general-purpose interface that can be used for almost any type of device, including modems, mice, and printers (although most printers are connected to a parallel port).


serif

A small decorative line added as embellishment to the basic form of a character. Typefaces are often described as being serif or sans serif (without serifs). The most common serif typeface is Times Roman. A common sans serif typeface is Helvetica.


server

A computer or device on a network that manages network resources. For example, a file server is a computer and storage device dedicated to storing files. Any user on the network can store files on the server. A print server is a computer that manages one or more printers, and a network server is a computer that manages network traffic. A database server is a computer system that processes database queries.

Servers are often dedicated, meaning that they perform no other tasks besides their server tasks. On multiprocessing operating systems, however, a single computer can execute several programs at once. A server in this case could refer to the program that is managing resources rather than the entire computer.


service

(1) See customer support.

(2) See online service.


service bureau

Short for prepress service bureau, a company that provides a variety of desktop publishing services. In particular, service bureaus have imagesetters that can produce high-resolution output on paper or film. This is a necessary step before printing a document with offset printing.

In addition to providing high-resolution output, many service bureaus also offer scanning services, as well as general consultancy. Some service bureaus have computers equipped with desktop publishing software which you can rent by the hour.


service provider

A company that provides access to the Internet. For a monthly fee, the service provider gives you a software package, username, password and access phone number. Equipped with a modem, you can then log on to the Internet and browse the World Wide Web and USENET, and send and receive e-mail.


setup

(v) To install and configure hardware or software. Most Windows applications come with a program called SETUP.EXE, which installs the software on the computer’s hard disk.

(n) The configuration of hardware or software.


SGML

Abbreviation of Standard Generalized Markup Language, a system for organizing and tagging elements of a document. SGML was developed and standardized by the International Organization for Standards (ISO) in 1986. SGML itself does not specify any particular formatting; rather, it specifies the rules for tagging elements. These tags can then be interpreted to format elements in different ways.

SGML is used widely to manage large documents that are subject to frequent revisions and need to be printed in different formats. Because it is a large and complex system, it is not yet widely used on personal computers. However, the growth of Internet, and especially the World Wide Web, is creating renewed interest in SGML because the World Wide Web uses HTML, which is one way of defining and interpreting tags according to SGML rules.


shadowing

A technique used to increase a computer's speed by using high-speed RAM memory in place of slower ROM memory. On PCs, for example, all code to control hardware devices, such as keyboards, is normally executed in a special ROM chip called the ROM-BIOS. However, this chip is slower than the general-purpose RAM that comprises main memory. Many PC manufacturers, therefore, copy the BIOS code into RAM when the computer boots. The RAM used to hold the BIOS code is called shadow RAM.


shareware

Software distributed on the basis of an honor system. Most shareware is delivered free of charge, but the author usually requests that you pay a small fee if you like the program and use it regularly. By sending the small fee, you become registered with the producer so that you can receive service assistance and updates. You can copy shareware and pass it along to friends and colleagues, but they too are expected to pay a fee if they use the product.

Shareware is inexpensive because it is usually produced by a single programmer and is offered directly to customers. Thus, there are practically no packaging or advertising expenses.

Shareware is available from a number of sources, including bulletin board services and online services. Note that shareware differs from public-domain software in that shareware is copyrighted. This means that you cannot sell a shareware product as your own.


sheet feeder

Also called cut-sheet feeder, a mechanism that holds a stack of paper and feeds each sheet into a printer one at a time. Sheet feeders are built into laser printers and are optional components for dot-matrix printers. Many fax machines also come with sheet feeders, as do some optical scanners.


shell

(1) The outermost layer of a program. Shell is another term for user interface. Operating systems and applications sometimes provide an alternative shell to make interaction with the program easier. For example, if the application is usually command driven, the shell might be a menu-driven system that translates the user's selections into the appropriate commands.

(2) Sometimes called command shell, a shell is the command processor interface. The command processor is the program that executes operating system commands. The shell, therefore, is the part of the command processor that accepts commands. After verifying that the commands are valid, the shell sends them to another part of the command processor to be executed.

UNIX systems offer a choice between several different shells, the most popular being the Cshell, the Bourne shell, and the Korn shell. Each offers a somewhat different command language.


shift clicking

Clicking a mouse button while holding the Shift key down. In Microsoft Windows and Macintosh systems, shift clicking enables you to select multiple items. Normally, when you select an item, the system deselects the previously selected item. However, if you shift click an item, the previously selected item(s) remain selected.


Shift key

A key on computer keyboards that gives the other keys an alternate meaning. When combined with alphabetic keys, the Shift key causes the system to output a capital letter. The Shift key can also be combined with other keys to produce program-dependent results.


shortcut key

A special key combination that causes a specific command to be executed. Typically, shortcut keys combine the Ctrl or Alt keys with some other keys. In Windows environments, for example, Ctrl+C is used as the shortcut key to copy. On PCs, the function keys are also often used as shortcut keys.

Most applications come with some shortcut keys already defined. Many, however, allow you to define your own shortcut keys for frequently-used commands.


shut down

(1) To turn the power off.

(2) Macintoshes have a “Shut Down” option in the Special menu. On newer Macs, selecting this option actually turns the computer off. On older Macs, it just prepares the computer to be manually turned off.


SIG

Acronym for special interest group, a group of users interested in a particular subject who discuss the subject at meetings or via an online service. SIGs exist for almost every conceivable subject. Online SIGs are sometimes called forums or conferences.


sign

A symbol that identifies a number as being either positive or negative. A positive sign is +; a negative sign is -. These two signs are also used to indicate addition and subtraction, respectively.


Silicon Valley

A nickname for the region north of San Francisco that contains an unusually high concentration of computer companies. Silicon is the most common semiconductor material used to produce chips.


SIMM

Acronym for single in-line memory module, a small circuit board that can hold a group of memory chips. Typically, SIMMs hold up 8 (on Macintoshes) or 9 (on PCs) RAM chips. On PCs, the ninth chip is for parity error checking. Unlike memory chips, SIMMs are measured in bytes rather than bits. In today’s SIMMs, each chip holds 2MB, so a single SIMM holds 16MB. SIMMs are easier to install than individual memory chips.


Simple Mail Transfer Protocol

A protocol for sending e-mail messages. Most e-mail systems that send mail over the Internet use SMTP for sending messages and POP to retieve messages. This is why you need to specify the POP server and the SMTP server when you configure your e-mail application.


simulation

The process of imitating a real phenomenon with a set of mathematical formulas. Advanced computer programs can simulate weather conditions, chemical reactions, atomic reactions, even biological processes. In theory, any phenomena that can be reduced to mathematical data and equations can be simulated on a computer. In practice, however, simulation is extremely difficult because most natural phenomena are subject to an almost infinite number of influences. One of the tricks to developing useful simulations, therefore, is to determine which are the most important factors.

In addition to imitating processes to see how they behave under different conditions, simulations are also used to test new theories. After creating a theory of causal relationships, the theorist can codify the relationships in the form of a computer program. If the program then behaves in the same way as the real process, there is a good chance that the proposed relationships are correct.


single in-line memory module

See SIMM.


single in-line package

See SIP.


single-density disk

A low-density floppy disk. All modern floppies are double-density or high-density.


single-sided disk

A floppy disk with only one side prepared for storing data. Single-sided disks have half as much storage capacity as double-sided disks. Most floppies are double-sided.


SIP

Abbreviation of single in-line package, a type of housing for electronic components in which the connecting pins protrude from one side. Compare with DIP and PGA.


size

To make an object larger or smaller. In graphical user interfaces, you can size windows to make them larger or smaller.

Other terms for size are resize and scale.


slate PC

A class of notebook computer that accepts input from an electronic pen rather than from a keyboard. Slate PCs are particularly useful in situations where keyboards are awkward or unnecessary. Typically, slate PCs can decipher clearly written block letters and translate them into their ASCII equivalents. To date, however, they cannot handle script, although the technology of handwriting recognition is progressing rapidly.


slave

Any device that is controlled by another device, called the master.


sleep mode

An energy-saving mode of operation in which all unnecessary components are shut down. Many battery-operated devices, such as notebook computers, support a sleep mode. When a notebook computer goes into sleep mode, it shuts down the display screen and disk drive. Once awakened, the computer returns to its former operating status.


slimline model

A small desktop model computer. See under desktop model computer.


SLIP

Short for Serial Line Internet Protocol, one of two methods for connecting to the Internet. The other method is PPP (Point-to-Point Protocol). SLIP is an older and simpler protocol, but from a practical perspective, there’s not much difference between connecting to the Internet via SLIP or PPP. In general, service providers offer only one protocol although some support both protocols.


slot

An opening in a computer where you can insert a printed circuit board. Slots are often called expansion slots because they allow you to expand the capabilities of a computer. The boards you insert in expansion slots are called expansion boards or add-on boards.

Do not confuse slots with bays. Bays are sites within the computer where you can install disk drives.


small computer system interface

See SCSI.


smart battery

See under battery pack.


smart terminal

A terminal that has some processing capabilities, but not as many as an intelligent terminal. Smart terminals have built-in logic for performing simple display operations, such as blinking and boldface. In contrast, a dumb terminal has no processing capabilities at all.


smiley

Same as emoticon.


smoothing

A technique used by some printers to make curves look smoother. Most printers that support smoothing implement it by reducing the dot size of the dots that make up a curved line. In addition, some printers can alter the horizontal alignment of dots to minimize jaggies.


SMTP

Short for Simple Mail Transfer Protocol.


soft

In computer science, soft is used to describe things that are intangible. For example, you cannot touch software. It's like music—you can see musical scores and touch CDs and tapes, but the music itself is intangible. Similarly, you can see software instructions (programs), and touch floppy disks on which the programs are stored, but the software itself is intangible.

Soft is also used to describe things that are easily changed or impermanent. In contrast, hard is used to describe things that are immutable.


soft font

A font that is copied from a computer’s disk to a printer's memory. Soft fonts can be erased, unlike resident fonts (fonts that are built into the printer) or font cartridges.

Soft fonts are generated by a font program in the computer. You can control the program to specify the font size and other characteristics. The disadvantages of soft fonts are that they require a lot of disk space and printer memory (from 10K to over 200K for a single font), and it takes time to download the fonts to the printer.

Soft fonts are also called downloadable fonts.


soft hyphen

See under hyphenation.


soft return

The term return refers to moving to the beginning of the next line in a text document. Word processors utilize two types of returns: hard and soft. In both cases, the return consists of special codes inserted into the document to cause the display screen, printer, or other output device to advance to the next line.

The difference between the two types of returns is that soft returns are inserted automatically by the word processor as part of its word wrap capability. Whenever too little room remains on the current line for the next word, the word processor inserts a soft return. The position of soft returns automatically changes, however, if you change the length of a line by adding or deleting words, or if you change the margins.

A hard return, on the other hand, always stays in the same place unless you explicitly delete it. Whenever you press the Return or Enter key, the word processor inserts a hard return. Hard returns are used to create new paragraphs or to align items in a table.


software

Computer instructions or data. Anything that can be stored electronically is software. The storage devices and display devices are hardware.

The terms software and hardware are used as both nouns and adjectives. For example, you can say: “The problem lies in the software,” meaning that there is a problem with the program or data, not with the computer itself. You can also say: “It's a software problem.”

The distinction between software and hardware is sometimes confusing because they are so integrally linked. Clearly, when you purchase a program, you are buying software. But to buy the software, you need to buy the disk (hardware) on which the software is recorded.

Software is often divided into two categories:

systems software: Includes the operating system and all the utilities that enable the computer to function.

applications software: Includes programs that do real work for users. For example, word processors, spreadsheets, and database management systems fall under the category of applications software.


software piracy

The unauthorized copying of software. Most retail programs are licensed for use at just one computer site or for use by only one user at any time. By buying the software, you become a licensed user rather than an owner. You are allowed to make copies of the program for backup purposes, but it is against the law to give copies to friends and colleagues.

Software piracy is all but impossible to stop, although software companies are launching more and more lawsuits against major infractors. Originally, software companies tried to stop software piracy by copy-protecting their software. This strategy failed, however, because it was inconvenient for users and was not 100 percent foolproof.

An entirely different approach to software piracy, called shareware, acknowledges the futility of trying to stop people from copying software and instead relies on people's honesty. Shareware publishers encourage users to give copies of programs to friends and colleagues but ask everyone who uses a program regularly to pay a registration fee to the program's author directly.


SOHO

Acronym for Small Office/Home Office, the fastest growing market for computer hardware and software. So-called SOHO products are specifically designed to meet the needs of professionals who work at home or in small offices.


solid ink-jet printer

A type of color printer that works by melting wax-based inks and then spraying them on paper. Solid ink-jet printers produce very vivid colors and can print on nearly any surface, but they are relatively slow and expensive.

Solid ink-jet printers are also called phase-change printers.


sound card

An expansion board that enables a computer to manipulate and output sounds. Sound cards are necessary for nearly all CD-ROMs and have become commonplace on modern personal computers. Sound cards enable the computer to output sound through speakers connected to the board, to record sound input from a microphone connected to the computer, and manipulate sound stored on a disk.

Nearly all sound cards support MIDI, a standard for representing music electronically. In addition, most sound cards are Sound Blaster-compatible, which means that they can process commands written for a Sound Blaster card, the de facto standard for PC sound.

Sound cards use two basic methods to translate digital data into analog sounds:

FM Synthesis mimics different musical instruments according to built-in formulas.

Wavetable Synthesis relies on recordings of actual instruments to produce sound. Wavetable synthesis produces more accurate sound, but is also more expensive.


source

A place from which data is taken. Many computer commands involve moving data. The place from which the data is moved is called the source, whereas the place it is moved to is called the destination or target. If you copy a file from one directory to another, for example, you copy it from the source directory to the destination directory. The source and destination can be files, directories, or devices (that is, printers or storage devices).


source code

Program instructions in their original form. The word source differentiates code from various other forms that it can have (for example, object code and executable code).

Initially, a programmer writes a program in a particular programming language. This form of the program is called the source program, or more generically, source code. To execute the program, however, the programmer must translate it into machine language, the language that the computer understands. The first step of this translation process is usually performed by a utility called a compiler. The compiler translates the source code into a form called object code. Sometimes the object code is the same as machine code; sometimes it needs to be translated into machine language by a utility called an assembler.

Source code is the only format that is readable by humans. When you purchase programs, you usually receive them in their machine-language format. This means that you can execute them directly, but you cannot read or modify them. Some software manufacturers provide source code, but this is useful only if you are an experienced programmer.


special character

A character that is not a letter, number, symbol, or punctuation mark. Control characters, for example, are special characters, as are special formatting characters such as paragraph marks.


special interest group

See SIG.


speech recognition

Same as voice recognition.


speech synthesis

Refers to a computer’s ability to produce sound that resembles human speech. Although they can’t imitate the full spectrum of human cadences and intonations, speech synthesis systems can read text files and output them in a very intelligible, if somewhat dull, voice. Many systems even allow the user to choose the type of voice—for example, male or female. Speech synthesis systems are particularly valuable for seeing-impaired individuals.


spell checker

A program that checks the spelling of words in a text document. Spell checkers are particularly valuable for catching typos, but they do not help when your misspelling creates another valid word; for example, you type too instead of to.

Many word processors come with a built-in spell checker, but you can also purchase stand-alone utilities.


spelling checker

See spell checker.


split screen

Division of the display screen into separate parts, each of which displays a different document, or different parts of the same document.


spooler

A program that controls spooling—putting jobs on a queue and taking them off one at a time. Most operating systems come with one or more spoolers, such as a print spooler for spooling documents. In addition, some applications include spoolers. Many word processors, for example, include their own print spooler.

A good print spooler should allow you to change the order of documents in the queue and to cancel specific print jobs.


spooling

Acronym for simultaneous peripheral operations on-line, spooling refers to putting jobs in a buffer, a special area in memory or on a disk where a device can access them when it is ready. Spooling is useful because devices access data at different rates. The buffer provides a waiting station where data can rest while the slower device catches up.

The most common spooling application is print spooling. In print spooling, documents are loaded into a buffer (usually an area on a disk), and then the printer pulls them off the buffer at its own rate. Because the documents are in a buffer where they can be accessed by the printer, you can perform other operations on the computer while the printing takes place in the background. Spooling also lets you place a number of print jobs on a queue instead of waiting for each one to finish before specifying the next one.


spot color

Refers to a method of specifying and printing colors in which each color is printed with its own ink. In contrast, process color printing uses four inks (cyan, magenta, yellow, and black) to produce all other colors. Spot color printing is effective when the printed matter contains only one to three different colors, but it becomes prohibitively expensive for more colors.

Most desktop publishing and graphics applications allow you to specify spot colors for text and other elements. There are a number of color specification systems for specifying spot colors, but Pantone is the most widely used.


spreadsheet

A table of values arranged in rows and columns. Each value can have a predefined relationship to the other values. If you change one value, therefore, you may need to change other values as well.

Spreadsheet applications (often referred to simply as spreadsheets) are computer programs that let you create and manipulate spreadsheets electronically. In a spreadsheet application, each value sits in a cell. You can define what type of data is in each cell and how different cells depend on one another. The relationships between cells are called formulas, and the names of the cells are called labels.

Once you have defined the cells and the formulas for linking them together, you can enter your data. You can then modify selected values to see how all the other values change accordingly. This enables you to study various what-if scenarios.

A simple example of a useful spreadsheet application is one that calculates mortgage payments for a house. You would define five cells:

1. total cost of the house

2. down payment

3. mortgage rate

4. mortgage term

5. monthly payment

Once you had defined how these cells depend on one another, you could enter numbers and play with various possibilities. For example, keeping all the other values the same, you could see how different mortgage rates would affect your monthly payments.

There are a number of spreadsheet applications on the market, Lotus 1-2-3 and Excel being among the most famous. The more powerful spreadsheet applications support graphics features that enable you to produce charts and graphs from the data.

Some spreadsheets are multidimensional, meaning that you can link one spreadsheet to another. A three-dimensional spreadsheet, for example, is like a stack of spreadsheets all connected by formulas. A change made in one spreadsheet automatically affects other spreadsheets.


SQL

Abbreviation of structured query language, and pronounced as separate letters. SQL is a standardized query language for requesting information from a database. The original version called SEQUEL (structured English query language) was designed by an IBM research center in 1974 and 1975. SQL was first introduced as a commercial database system in 1979 by Oracle Corporation.

Historically, SQL has been the favorite database management system for minicomputers and mainframes. Increasingly, however, SQL is being supported by PC database systems because it supports distributed databases (databases that are spread out over several computer systems). This enables several users on a local-area network to access the same database simultaneously.

Although there are different dialects of SQL, it is nevertheless the closest thing to a standard query language that currently exists. In 1986, ANSI approved a rudimentary version of SQL as the official standard, but most versions of SQL since then have included many extensions to the ANSI standard. In 1991, ANSI updated the standard. The new standard is known as SAG SQL.


SRAM

Short for static random access memory, and pronounced ess-ram. SRAM is a type of memory that is faster and more reliable than the more common DRAM (dynamic RAM). The term static is derived from the fact that it needs to be refreshed less often than dynamic RAM.

While DRAM supports access times of about 60 nanoseconds, SRAM can give access times as low as 10 nanoseconds. In addition, its cycle time is much shorter than that of DRAM because it does not need to pause between accesses. Unfortunately, it is also much more expensive to produce than DRAM. Due to its high speed, SRAM is often used as a memory cache.


ST-412 interface

Same as ST-506 interface.


ST-506 interface

A standard interface for connecting hard disk drives to PCs. Newer standards, such as enhanced IDE and SCSI, support faster data transfer rates.

ST-506 is sometimes referred to as MFM, which is the most prevalent encoding scheme used on ST-506 disk drives. ST-506 also supports the RLL encoding format.


stack

(1) In programming, a special type of data structure in which items are removed in the reverse order from that in which they are added, so the most recently added item is the first one removed. This is also called last-in, first-out (LIFO).

Adding an item to a stack is called pushing. Removing an item from a stack is called popping.

(2) In Apple Computer's HyperCard software system, a stack is a collection of cards.


stand-alone

Refers to a device that is self-contained, one that does not require any other devices to function. For example, a fax machine is a stand-alone device because it does not require a computer, printer, modem, or other device. A printer, on the other hand, is not a stand-alone device because it requires a computer to feed it data.


standard

A definition or format that has been approved by a recognized standards organization or is accepted as a de facto standard by the industry. Standards exist for programming languages, operating systems, data formats, communications protocols, and electrical interfaces.

From a user's standpoint, standards are extremely important in the computer industry because they allow the combination of products from different manufacturers to create a customized system. Without standards, only hardware and software from the same company could be used together. In addition, standard user interfaces can make it much easier to learn how to use new applications.

Most official computer standards are set by one of the following organizations:

•	ANSI (American National Standards Institute)

•	CCITT (Comité Consultatif Internationale Télégraphique et Téléphonique)

•	IEEE (Institute of Electrical and Electronic Engineers)

•	ISO (International Standards Organization)

•	VESA (Video Electronics Standards Association)

IEEE sets standards for most types of electrical interfaces. Its most famous standard is probably RS-232C, which defines an interface for serial communication. This is the interface used by most modems, and a number of other devices, including display screens and mice. IEEE is also responsible for designing floating-point data formats.

While IEEE is generally concerned with hardware, ANSI is primarily concerned with software. ANSI has defined standards for a number of programming languages, including C, COBOL, and FORTRAN.

CCITT defines international standards, particularly communications protocols. It has defined a number of standards, including V.22, V.32, V.34 and V.42, that specify protocols for transmitting data over telephone lines.

In addition to standards approved by organizations, there are also de facto standards. These are formats that have become standard simply because a large number of companies have agreed to use them. They have not been formally approved as standards, but they are standards nonetheless. PostScript is a good example of a de facto standard.


Standard Generalized Markup Language

See SGML.


standard input

The place from which input comes unless you specify a different input device. The standard input device is usually the keyboard.


standard output

The place where output goes unless you specify a different output device. The standard output device is usually the display screen.


star network

A local-area network (LAN) that uses a star topology in which all nodes are connected to a central computer. The main disadvantage of star networks is that they require more cabling than other topologies, such as a bus or ring networks. In addition, if the central computer fails, the entire network becomes unusable.


start bit

In asynchronous communications, the bit that signals the receiver that data is coming. Every byte of data is preceded by a start bit and followed by a stop bit.


start-stop transmission

See under asynchronous.


statement

An instruction written in a high-level language. A statement directs the computer to perform a specified action. A single statement in a high-level language can represent several machine-language instructions. Programs consist of statements and expressions. An expression is a group of symbols that represent a value.


static RAM

See SRAM.


static variable

A variable that retains the same data throughout the execution of a program. In contrast, a dynamic variable can have different values during the course of a program.


station

Short for workstation.


stop bit

In asynchronous communications, a bit that indicates that a byte has just been transmitted. Every byte of data is preceded by a start bit and followed by a stop bit.


storage

The capacity of a device to hold and retain data.


storage device

A device capable of storing data. The term usually refers to mass storage devices, such as disk and tape drives.


store

To copy data from a CPU to memory, or from memory to a mass storage device.


streamer

Same as tape.


strikeout

A method of highlighting text by drawing a horizontal line through the characters. This text, for example, has strikeout formatting.

Many word processors support edit modes in which deleted sections are displayed with strikeouts. This is particularly effective in workgroups where two or more people are editing the same document.

Strikeout is also called strikethrough.


strikethrough

Same as strikeout.


string

See character string.


Structured Query Language

See SQL.


style

In word processing, a named set of formatting parameters. By applying the style name to a section of text, you can change many formatting properties at once.


style sheet

In word processing and desktop publishing, a style sheet is a file or form that defines the layout of a document. When you fill in a style sheet, you specify such parameters as the page size, margins, and fonts. Style sheets are useful because you can use the same style sheet for many documents. For example, you could define one style sheet for personal letters, another for official letters, and a third for reports.

Stylesheets are also called templates.


stylus

A pointing and drawing device shaped like a pen. You use a stylus with a graphics tablet or touch screen.


subdirectory

A directory below another directory. Every directory except the root directory is a subdirectory. On Macintosh computers, subdirectories are called folders.


subnotebook computer

A portable computer that is slightly lighter and smaller than a full-sized notebook computer. Typically, subnotebook computers have a smaller keyboard and screen, but are otherwise equivalent to notebook computers.


subroutine

Same as routine.


subscript

(1) In programming, a symbol or number used to identify an element in an array. Usually, the subscript is placed in brackets following the array name. For example, AR[5] identifies element number 5 in an array called AR.

If the array is multidimensional, you must specify a subscript for each dimension. For example, MD[5][3][9] identifies an element in a three-dimensional array called MD.

Different programming languages have different rules for specifying subscripts. For example, the BASIC language uses parentheses in place of brackets.

(2) In word processing, a character that appears slightly below the line, as in this example: H20. A superscript is a character that appears slightly above the line.


Super VGA

See SVGA.


supercomputer

The fastest type of computer. Supercomputers are very expensive and are employed for specialized applications that require immense amounts of mathematical calculations. For example, weather forecasting requires a supercomputer. Other uses of supercomputers include animated graphics, fluid dynamic calculations, nuclear energy research, and petroleum exploration.

The chief difference between a supercomputer and a mainframe is that a supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs concurrently.


SuperDrive

The common name for the FDHD (floppy disk, high density) disk drive that comes with all models of the Apple Macintosh computer. The SuperDrive can read and write to all three Macintosh disk sizes (400K, 800K, and 1.2MB) as well as the two IBM 3½-inch disk sizes (720K and 1.44MB).


superscript

A symbol or character that appears slightly above a line, as in this example: r2. Footnote numbers appearing in text are also superscripts. A symbol or character that appears slightly below a line is called a subscript.


supertwist

A technique for improving LCD display screens by twisting light rays. In addition to normal supertwist displays, there also exist double supertwist and triple supertwist displays. In general, the more twists, the higher the contrast.


support

(v) To have a specific functionality. For example, a word processor that supports graphics is one that has a graphics component. The word support, however, is vague. It could mean that the word processor enables you to create graphics illustrations, that you can insert graphics created by another program, or something entirely different.

As another example, an operating system that supports multiple users is one that enables several users to run programs at the same time.

(n) Short for customer support, the assistance that a vendor offers to customers. Support can vary widely, from nothing at all to a phone hotline to house calls.


surf

To move from place to place on the Internet searching for topics of interest.  Web surfing has become a favorite pastime for many Internet users. The links on each page enable you to start virtually anywhere on the Web and eventually find interesting pages. The term surfing is generally used  to describe a rather undirected type of Web browsing in which the user jumps from page to page rather whimsically, as opposed to specifically searching for specific information.


surge protector

A device that protects a power supply from electrical surges. All computers come with some surge protection built into the power supply, but it is a good idea to purchase a separate device. A more robust form of protection from electrical disturbances is called an uninterruptible power supply (UPS).


SVGA

Short for Super VGA, a set of graphics standards designed to offer greater resolution than VGA. There are several varieties of SVGA, each providing a different resolution:

•	800 by 600 pixels

•	1024 by 768 pixels

•	1280 by 1024 pixels

•	1600 by 1200 pixels

All SVGA standards support a palette of 16 million colors, but the number of colors that can be displayed simultaneously is limited by the amount of video memory installed in a system. One SVGA system might display only 16 simultaneous colors while another displays the entire palette of 16 million colors. The SVGA standards are developed by a consortium of monitor and graphics manufacturers called VESA.


swap

(1) To replace pages or segments of data in memory. Swapping is a useful technique that enables a computer to execute programs and manipulate data files larger than main memory. The operating system copies as much data as possible into main memory, and leaves the rest on the disk. When the operating system needs data from the disk, it exchanges a portion of data (called a page or segment) in main memory with a portion of data on the disk.

DOS does not perform swapping, but most other operating systems, including OS/2, Windows, and UNIX, do.

Swapping is often called paging.

(2) In UNIX systems, swapping refers to moving entire processes in and out of main memory.


swap file

In Windows environments, a hidden file used by the operating system for swapping.


switch

(1) A small lever or button. The switches on the back of printers and on expansion boards are called DIP switches. A switch that has just two positions is called a toggle switch.

(2) Another word for option or parameter—a symbol that you add to a command to modify the command's behavior.


synchronous

Occurring at regular intervals. The opposite of synchronous is asynchronous. Most communication between computers and devices is asynchronous—it can occur at any time and at irregular intervals. Communication within a computer, however, is usually synchronous and is governed by the microprocessor clock. Signals along the bus, for example, can occur only at specific points in the clock cycle.


syntax

Refers to the spelling and grammar of a programming language. Computers are inflexible machines that understand what you type only if you type it in the exact form that the computer expects. The expected form is called the syntax.

Each program defines its own syntactical rules that control which words the computer understands, which combinations of words are meaningful, and what punctuation is necessary.


sysop

Pronounced siss-op, short for system operator, an individual who manages a bulletin board system (BBS), online service, or special interest group (SIG).


System

On Macintoshes, System is short for System file, an essential program that runs whenever you start up a Macintosh. The System provides information to all other applications that run on a Macintosh. The System and Finder programs together make up the Macintosh operating system.


system

(1) Refers to a combination of components working together. For example, a computer system includes both hardware and software. A Windows system is a personal computer running the Windows operating system. A desktop publishing system is a computer running desktop publishing software.

(2) Short for computer system.

(3) Short for operating system.

(4) An organization or methodology. The binary  numbering system, for instance, is a way to count using only two digits.


system board

Same as motherboard.


system call

The invocation of an operating system routine. Operating systems contain sets of routines for performing various low-level operations. For example, all operating systems have a routine for creating a directory. If you want to execute an operating system routine from a program, you must make a system call.


System folder

A standard folder on Macintoshes that contains the System and Finder programs, as well as other resources needed by the operating system.


system prompt

See under prompt.


system unit

The main part of a personal computer. The system unit includes the chassis, microprocessor, main memory, bus, and ports, but does not include the keyboard or monitor, or any peripheral devices.


systems analyst

A programmer or consultant who designs and manages the development of business applications. Typically, systems analysts are more involved in design issues than in day-to-day coding. However, systems analyst is a somewhat arbitrary title, so different companies define the role differently.


systems software

Refers to the operating system and all utility programs that manage computer resources at a low level. Software is generally divided into systems software and applications software. Applications software comprises programs designed for an end user, such as word processors, database systems, and spreadsheet programs. Systems software includes compilers, loaders, linkers, and debuggers.


tab character

A special character that can be inserted into a text document.

Different programs react to tab characters in different ways. Most word processors, for example, move the cursor or insertion point to the next tab stop, and most printers move the print head to the next tab stop as well. Some programs, however, simply ignore tabs.


Tab key

A key on computer keyboards that inserts a tab character or moves the insertion point to the next tab stop. Some applications respond to the tab key by inserting spaces up to the next tab stop. This is often called a soft tab, whereas a real tab character is called a hard tab.

Spreadsheet and database management applications usually respond to the Tab key by moving the cursor to the next field or cell. In dialog boxes and menus, pressing the Tab key highlights the next button or option.


tab stop

A stop point for tabbing. In word processing, each line contains a number of tab stops placed at regular intervals (for example, every half inch). They can be changed, however, as most word processors allow you to set tab stops wherever you want. When you press the Tab key, the cursor or insertion point jumps to the next tab stop, which itself is invisible. Although tab stops do not exist in the text file, the word processor keeps track of them so that it can react correctly to the Tab key.


table

Refers to data arranged in rows and columns. A spreadsheet, for example, is a table. In relational database management systems, all information is stored in the form of tables.


tablet

Short for graphics tablet, digitizing tablet, or electronic tablet.


Tagged Image File Format

See TIFF.


tape

A magnetically coated strip of plastic on which data can be encoded. Tapes for computers are similar to tapes used to store music. Some personal computers, in fact, enable you to use normal cassette tapes.

Storing data on tapes is considerably cheaper than storing data on disks. Tapes also have large storage capacities, ranging from a few hundred kilobytes to several gigabytes. Accessing data on tapes, however, is much slower than accessing data on disks. Tapes are sequential-access media, which means that to get to a particular point on the tape, the tape must go through all the preceding points. In contrast, disks are random-access media because a disk drive can access any point at random without passing through intervening points.

Because tapes are so slow, they are generally used only for long-term storage and backup. Data to be used regularly is almost always kept on a disk. Tapes are also used for transporting large amounts of data.

Tapes come in a variety of sizes and formats.

Tapes are sometimes called streamers or streaming tapes.


tape drive

A device, like a tape recorder, that reads data from and writes it onto a tape. Tape drives have data capacities of anywhere from a few hundred kilobytes to several gigabytes. Their transfer speeds also vary considerably. Fast tape drives can transfer as much as 20MB (megabytes) per minute.

The disadvantage of tape drives is that they are sequential-access devices, which means that to read any particular block of data, you need to read all the preceding blocks. This makes them much too slow for general-purpose storage operations. However, they are the least expensive media for making backups.


target

Synonymous with destination, a target is a file or device to which data is moved or copied. Many computer commands involve copying data from one place to another. One says that the computer copies from the source to the target (or destination).


task

An operating system concept that refers to the combination of a program being executed and bookkeeping information used by the operating system. Whenever you execute a program, the operating system creates a new task for it. The task is like an envelope for the program: it identifies the program with a task number and attaches other bookkeeping information to it.

Many operating systems, including UNIX, OS/2, and Windows, are capable of running many tasks at the same time and are called multitasking operating systems.

In most operating systems, there is a one-to-one relationship between the task and the program, but some operating systems allow a program to be divided into multiple tasks. Such systems are called multithreading operating systems.


task switching

Refers to operating systems or operating environments that enable you to switch from one program to another without losing your spot in the first program. Many utilities are available that add task switching to DOS systems.

Note that task switching is not the same as multitasking. In multitasking, the CPU switches back and forth quickly between programs, giving the appearance that all programs are running simultaneously. In task switching, the CPU does not switch back and forth, but executes only one program at a time. Task switching does allow you to switch smoothly from one program to another.

Task switching is sometimes called context switching.


TCP/IP

Acronym for Transport Control Protocol/Internet Protocol, a communications protocol developed by the Department of Defense. TCP/IP is actually two protocols—TCP and IP—but they are almost always used together. TCP/IP is built into the UNIX operating system and is used by the Internet, making it the de facto standard for transmitting data over networks. Even network operating systems that have their own protocols, such as Netware, also support TCP/IP.


tear-off menu

A pop-up menu that you can move around the screen like a window. Regular pop-up menus are attached to the menu selection that caused them to pop up.


technical support

See customer support.


telecommunications

Refers to all types of data transmission, from voice to video.


telecommuting

A term coined by Jack Nilles in the early 1970s to describe a geographically dispersed office where workers can work at home on a computer and transmit data and documents to a central office via telephone lines. A major argument in favor of telecommuting over vehicular commuting is that it does not produce air pollution. In addition, many people are more productive working at home than in an office. For others, however, the contrary holds true.


telecopy

To send a document from one place to another via a fax machine.


Telenet

One of the largest public data networks (PDNs) in the United States. Telenet is owned by U.S. Sprint Communications Corporation. A competing network, called Tymnet, is owned by McDonnell Douglas. Telenet serves as the communications backbone for many online services.


template

(1) A plastic or paper diagram that you can put on your keyboard to indicate the meanings of different keys for a particular program.

(2) A sheet of plastic with menus and command boxes drawn on it that you place on top of a digitizing tablet. You can select commands by pressing the digitizing tablet's pen against a command box or by positioning the cursor over a box and pressing one of the cursor keys.

(3) In spreadsheet and database applications, a template is a blank form that shows which fields exist, their locations, and their length. In spreadsheet applications, for example, a template is a spreadsheet in which all the cells have been defined but no data has yet been entered.

(4) In some word processing applications, template is used in place of style sheet.

(5) DOS uses the term template to mean command buffer.


terabyte

240 (1,099,511,627,776) bytes. This is approximately 1 trillion bytes.


terminal

(1) A device that enables you to communicate with a computer. Generally, a terminal is a combination of keyboard and display screen.

Terminals are sometimes divided into three classes based on how much processing power they contain:

intelligent terminal: A stand-alone device that contains main memory and a CPU.

smart terminal: Contains some processing power, but not as much as an intelligent terminal.

dumb terminal: Has no processing capabilities. It relies entirely on the computer's processor.

(2) In networking, a terminal is a personal computer or workstation connected to a mainframe. The personal computer usually runs terminal emulation software that makes the mainframe think it is like any other mainframe terminal.


terminal emulation

Refers to making a computer respond like a particular type of terminal. Terminal emulation programs allow you to access a mainframe computer or bulletin board service with a personal computer.


terminate and stay resident

See TSR.


Texas Instruments Graphics Architecture (TIGA)

A high-resolution graphics specification designed by Texas Instruments. Unlike other graphics standards, TIGA does not specify a particular resolution or number of colors. Instead, it defines an interface between software and graphics processors. Programs written for TIGA, therefore, should be able to run on future systems that conform to the TIGA standard, regardless of resolution and color specifics.

Currently, the only graphics standard that conforms to TIGA is TI 34010, which defines a resolution of 1,024 by 768, with 256 simultaneous colors. Two competing standards with the same resolution are 8514/A from IBM and SVGA from VESA.


text

Words, sentences, paragraphs. This book, for example, consists of text. Text processing refers to the ability to manipulate words, lines, and pages. Typically, the term text refers to text stored as ASCII codes (that is, without any formatting). Objects that are not text include graphics, numbers (if they’re not stored as ASCII characters), and program code.


text editor

See editor.


text file

A file that holds text. The term text file is often used as a synonym for ASCII file, a file in which characters are represented by their ASCII codes.


text flow

Same as text wrap.


text mode

A video mode in which a display screen is divided into rows and columns of boxes. Each box can contain one character. Text mode is also called character mode.

All video standards for the PC, including VGA, support a text mode that divides the screen into 25 rows and 80 columns. In addition to text mode, most video adapters support a graphics mode, in which the display screen is divided into an array of pixels.

Whereas character-based programs run in text mode, all graphics-based programs run in graphics mode.


text wrap

A feature supported by many word processors that enables you to surround a picture or diagram with text. The text wraps around the graphic. Text wrap is also called text flow.


TFT

Abbreviation of thin film transistor, a type of LCD flat-panel display screen, in which each pixel is controlled by from one to four transistors. The TFT technology provides the best resolution of all the flat-panel techniques, but it is also the most expensive. TFT screens are sometimes called active-matrix LCDs.


thermal printer

A type of printer that produces images by pushing electrically heated pins against special heat-sensitive paper. Thermal printers are inexpensive and are used in most calculators and many fax machines. They produce low-quality print, and the paper tends to curl and fade after a few weeks or months.


thin film transistor

See TFT.


thread

(1) In online discussions, a series of messages that have been posted as replies to each other. A single forum or conference typically contains many threads covering different subjects. By reading each message in a thread, one after the other, you can see how the discussion has evolved. You can start a new thread by posting a message that is not a reply to an earlier message.

(2) In programming, a part of a program that can execute independently of other parts. Operating systems that support multithreading enable programmers to design programs whose threaded parts can execute concurrently.


three-dimensional spreadsheet

A spreadsheet program that allows you to arrange data as a stack of tables, each of which has the same shape and size. You can analyze a single table or an entire group of tables.


throughput

The amount of data transferred from one place to another or processed in a specified amount of time. Data transfer rates for disk drives and networks are measured in terms of throughput. Typically, throughputs are measured in bits per second (bps).


thumbnail

A miniature display of a page to be printed. Thumbnails enable you to see the layout of many pages on the screen at once. Generally, thumbnails are too small to show the actual text, so greeking is used to indicate how the text will look.


TI 34010

A video standard from Texas Instruments that supports a resolution of 1,024 by 768. TI 34010 conforms to TI's Graphics Architecture (TIGA). Unlike IBM's 8514/A, which supports the same resolution, TI 34010 is noninterlaced.


TIFF

Acronym for tagged image file format, one of the most widely supported file formats for storing bit-mapped images on personal computers (both PCs and Macintosh computers). Other popular formats are BMP and PCX.

TIFF graphics can be any resolution, and they can be black and white, gray-scaled, or color.


TIGA

See Texas Instruments Graphics Architecture.


tiled windows

Windows arranged so that they do not overlap each other. Overlapping windows are often called overlaid or cascading windows.


time sharing

Refers to the concurrent use of a computer by more than one user—users share the computer's time. Time sharing is synonymous with multi-user. Almost all mainframes and minicomputers are time-sharing systems, but most personal computers and workstations are not.


time-out

An interrupt signal generated by a program that has waited a certain length of time for some input but has not received it. Many programs perform time-outs so that the program does not sit idle waiting for input that may never come. For example, automatic bank-teller machines perform a time-out if you do not enter your password quickly enough.


title bar

A bar on top of a window. The title bar contains the name of the file or application. In many graphical user interfaces, including the Macintosh and Microsoft Windows interfaces, you move (drag) a window by grabbing the title bar.


toggle

To switch from one setting to another. The term toggle implies that there are only two possible settings and that you are switching from the current setting to the other setting.

A toggle switch is a switch that has just two positions. For example, light switches that turn a light on or off are toggle switches. On computer keyboards, the Caps Lock key is a toggle switch because pressing it can have two meanings depending on what the current setting is. If Caps Lock is already on, then pressing the Caps Lock key turns it off. If Caps Lock is off, pressing the Caps Lock key turns it on.


token

(1) In programming languages, a single element of a programming language. For example, a token could be a keyword, an operator, or a punctuation mark.

(2) In networking, a token is a special series of bits that travels around a token-ring network. As the token circulates, computers attached to the network can capture it. The token acts like a ticket, enabling its owner to send a message across the network. There is only one token for each network, so there is no possibility that two computers will attempt to transmit messages at the same time.


token-ring network

(1) A type of computer network in which all the computers are arranged (schematically) in a circle. A token, which is a special bit pattern, travels around the circle. To send a message, a computer catches the token, attaches a message to it, and then lets it continue to travel around the network.

(2) When capitalized, Token Ring refers to the PC network protocol developed by IBM. The IBM Token-Ring specification has been standardized by the IEEE as the IEEE 802.5 standard.


toner

A special type of ink used by copy machines and laser printers. Toner consists of a dry, powdery substance that is electrically charged so that it adheres to a drum, plate, or piece of paper charged with the opposite polarity.

For most laser printers, the toner comes in a cartridge that you insert into the printer. When the cartridge is empty, you can replace it or have it refilled. Typically, you can print thousands of pages with a single cartridge.


topology

The shape of a local-area network (LAN). There are three principal topologies used in LANs.

bus topology: All devices are connected to a central cable, called the bus or backbone. Bus networks are relatively inexpensive and easy to install. Ethernet systems use a bus topology.

ring topology: All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. Ring topologies are relatively expensive and difficult to install, but they are robust (one failed device does not usually make the entire network fail).

star topology: All devices are connected to a central hub. Star networks are relatively easy to install and manage, but bottlenecks can occur because all data must pass through the hub.


TOPS

Acronym for transparent operating system, a type of local-area network designed by Sun Microsystems that can combine Apple Macintosh computers, PCs, and Sun workstations on the same network. A particular strength of TOPS is that the networking software is transparent, meaning that users do not need to adjust to a new operating environment. PC users see their PC interface and Mac users see the Mac interface.

TOPS uses the Macintosh computer's built-in AppleTalk protocol. It is a peer-to-peer network, which means that it does not require any computers to be set aside as file servers. Authorized users can access files from any disk drive connected to the network.


touch screen

A type of display screen that has a touch-sensitive transparent panel covering the screen. Instead of using a pointing device such as a mouse or light pen, you can use your finger to point directly to objects on the screen.

Although touch screens provide a natural interface for computer novices, they are unsatisfactory for most applications because the finger is such a relatively large object. It is impossible to point accurately to small areas of the screen. In addition, most users find touch screens tiring to the arms after long use.


touch tablet

Same as digitizing tablet.


touchpad

A small, touch-sensitive pad used as a pointing device on some portable computers. By moving a finger or other object along the pad, you can move the pointer on the display screen.


tower model

Refers to a computer in which the power supply, motherboard, and mass storage devices are stacked on top of each other in a cabinet. This is in contrast to desktop models, in which these components are housed in a more compact box.

The main advantage of tower models is that there are fewer space constraints, which makes installation of additional storage devices easier. Traditional tower models are about 21 inches tall. Many computer manufacturers now offer minitower models, which are about 14 inches tall, and mid-sized tower models, which are about 16 inches tall..


TPI

Short for tracks per inch, the density of tracks on a disk. For example, double-density 5.25-inch floppies have a TPI of 48, while high-density floppies record 96 TPI. High-density 3.25-inch diskettes are formatted with 135 TPI.


track

A ring on a disk where data can be written. A typical floppy disk has 80 (double-density) or 160 (high-density) tracks. For hard disks, each platter is divided into tracks, and a single track location that cuts through all platters is called a cylinder. Hard disks can have anywhere from 400 to more than 1000 cylinders.

Each track is further divided into a number of sectors. The operating system and disk drive remember where information is stored by noting its track and sector numbers.

The density of tracks (how close together they are) is measured in terms of tracks per inch (TPI).


trackball

A pointing device. Essentially, a trackball is a mouse lying on its back. To move the pointer, you rotate the ball with your thumb, your fingers, or the palm of your hand. There are usually one to three buttons next to the ball, which you use just like mouse buttons.

The advantage of trackballs over mice is that the trackball is stationary so it does not require much space to use it. In addition, you can place a trackball on any type of surface, including your lap. For both these reasons, trackballs are popular pointing devices for portable computers.


tracks per inch

See TPI.


tractor feed

A method of feeding paper through a printer. Tractor-feed printers have two sprocketed wheels on either side of the printer that fit into holes in the paper. As the wheels revolve, the paper is pulled through the printer. Tractor feed is also called pin feed.

The other principal form of feeding paper into a printer is friction feed, which utilizes plastic or rubber rollers to squeeze a sheet of paper and pull it through the printer.

Tractor-feed printers require special paper (with holes), whereas friction feed printers can handle most types of cut-sheet paper, including envelopes. Some printers support both types of feeding mechanisms.


traffic

The load on a communications device or system. One of the principal jobs of a system administrator is to monitor traffic levels and take appropriate actions when traffic becomes heavy.


transaction processing

A type of computer processing in which the computer responds immediately to user requests. Each request is considered to be a transaction. Automatic teller machines for banks are an example of transaction processing.

The opposite of transaction processing is batch processing, in which a batch of requests is stored and then executed all at one time. Transaction processing requires interaction with a user, whereas batch processing can take place without a user being present.


Transfer Control Protocol/Internet Protocol

See TCP/IP.


transparent

Invisible. In computer software, an action is transparent if it takes place without any visible effect. Transparency is usually considered to be a good characteristic of a system because it shields the user from the system's complexity.


transportable

A large portable computer (over 15 pounds). Another term for transportable is luggable.


tree structure

A type of data structure in which each element is attached to one or more elements directly beneath it. The connections between elements are called branches. Trees are often called inverted trees because they are normally drawn with the root at the top.

The elements at the very bottom of an inverted tree (that is, those that have no elements below them) are called leaves. Inverted trees are the data structures used to represent hierarchical file structures. In this case, the leaves are files and the other elements above the leaves are directories.

A binary  tree is a special type of inverted tree in which each element has only two branches below it.


true color

Refers to any graphics device or software that uses at least 24 bits to represent each dot or pixel. Using 24 bits means that more than 16 million unique colors can be represented. Since humans can only distinguish a few million colors, this is more than enough to accurately represent any color image.


TrueType

An outline font technology developed jointly by Microsoft and Apple. Because TrueType support is built into all Windows and Macintosh operating systems, anyone using these operating systems can create documents using TrueType fonts.

Since being introduced in 1991, TrueType has quickly become the dominant font technology for everyday use, and is even displacing PostScript in many publishing environments.


truncate

To cut off the end of something. Usually, the term is used to describe a type of rounding of floating-point numbers. For example, if there are too few spaces for a long floating-point number, a program may truncate the number by lopping off the decimal digits that do not fit: 3.14126 might be truncated to 3.14. Note that truncation always rounds the number down. If the number 1.19999 is truncated to one decimal digit, it becomes 1.1, not 1.2.


TSR

Abbreviation of terminate and stay resident. Refers to DOS programs that can be memory resident (remaining in memory at all times once they are loaded). Calendars, calculators, spell checkers, thesauruses, and notepads are often set up as TSRs so that you can instantly access them from within another program. TSRs are sometimes called pop-up programs because they can pop up in applications.

When you install a TSR, you define a special key sequence (usually a control character) that will invoke the TSR program. You can then press this hot key from within any application to run the TSR program. Many programs can be installed as a TSR, but TSRs reduce the amount of memory available to other programs. In addition, not all TSRs interact well with each other. You may have difficulties, therefore, if you try to keep too many TSRs in main memory at once.

TSRs are unnecessary with multitasking operating systems such as Windows, OS/2, and the Mac OS.


TTL monitor

TTL stands for transistor-transistor logic and refers to a special type of digital circuit. More commonly, however, TTL is used to designate any type of digital input or device. A TTL monitor, therefore, is a monitor that accepts digital input. TTL monitors are consistent with older graphics standards such as MDA, but all newer graphics standards, including VGA, require analog signals. Some monitors can accept both types of signal.


turnkey system

A computer system that has been customized for a particular application. The term derives from the idea that the end user can just turn a key and the system is ready to go. Turnkey systems include all the hardware and software necessary for the particular application. They are usually developed by OEMs (original equipment manufacturers) who buy a computer from another company and then add software and devices themselves.


TWAIN

Acronym for Technology Without An Interesting Name, the de facto interface standard for scanners. Nearly all scanners come with a TWAIN driver, which makes them compatible with any TWAIN-supporting software. Unfortunately, not all scanner software is TWAIN-compatible.


tweak

To make small changes that fine-tune a piece of software or hardware. Tweaking sometimes refers to changing the values of underlying variables slightly to make the results of a program coincide with desired results. In this case, tweaking is not always a good thing since it undermines the integrity of the program.


twisted-pair cable

A type of cable that consists of two independently insulated wires twisted around one another. One wire carries the signal while the other wire is grounded and absorbs signal interference. Twisted-pair cable is used by older telephone networks and is the least expensive type of local-area network (LAN) cable. Other types of cables used for LANs include coaxial cables and fiber optic cables.


Tymnet

One of the largest public data networks (PDNs) in the United States. Tymnet is owned by McDonnell Douglas Corporation. A competing network, called Telenet, is owned by U.S. Sprint Communications Corporation.


type

(v) (1) To enter characters by pressing keys on the keyboard.

(2) In DOS, OS/2, and many other operating systems, the TYPE command causes a file to appear on the display screen.

(n) Short for data type.


typeface

A design for a set of characters. Popular typefaces include Times Roman, Helvetica, and Courier. The typeface represents one aspect of a font. The font also includes such characteristics as size, weight, italics, and so on.

There are two general categories of typefaces: serif and sans serif. Sans serif typefaces are composed of simple lines, whereas serif typefaces use small decorative marks to embellish characters. Helvetica is a sans serif type and Times Roman is a serif type.


typesetter

Same as imagesetter.


UART

Pronounced u-art, and short for universal asynchronous receiver-transmitter, the UART is a computer component that handles asynchronous serial communication. Every computer contains a UART to manage the serial ports, and all internal modems have their own UART.

As modems have become increasingly fast, the UART has come under greater scrutiny as the cause of transmission bottlenecks. If you are purchasing a fast external modem, make sure that the computer’s UART can handle the modem’s maximum transmission rate. The newer 16550 UART contains a 16-bit buffer, enabling it to support higher transmission rates than the older 8250 UART.


ULSI

Abbreviation of ultra large scale integration, which refers to placing more than one million circuit elements on a single chip. The Intel 486 and Pentium microprocessors, for example, use ULSI technology.


ultra large scale integration

See ULSI.


underflow

Refers to the condition that occurs when a computer attempts to represent a number that is too small for it. Programs respond to underflow conditions in different ways. Some report an error, while others approximate as best they can and continue processing.


undo

To return to a previous state by undoing the effects of one or more commands. The undo command is a valuable feature supported by many software products. It lets you try unknown commands with less risk, because you can always return to the previous state. Also, if you accidentally press the wrong function key, you can undo your mistake.

Many programs allow you to undo an unlimited number of commands. Each time you press the undo key, the previous command is undone. You can roll back an entire editing session this way. Other programs impose a limit on the number of commands you can undo.


undocumented

Refers to features that are not described in the official documentation of a product. This lack of documentation can occur for a variety of reasons, including oversight. More often, though, undocumented features are features that were included because they were useful to the programmers developing the product but were deemed either unnecessary or potentially dangerous to end users. Undocumented features can also include untested features that will be officially supported in a future release of the product.


Unicode

A standard for representing characters as integers. Unlike ASCII, which uses 8 bits for each character, Unicode uses 16 bits, which means that it can represent more than 65,000 unique characters. This is a bit of overkill for English and European languages, but it is necessary for some other languages, such as Chinese and Japanese. Many analysts believe that as the software industry becomes increasingly global, Unicode will eventually supplant ASCII as the standard character coding format.


Uniform Resource Locator

See URL.


uninterruptible power supply

See UPS.


universal asynchronous receiver-transmitter

See UART.


UNIX

Pronounced yoo-niks, a popular multi-user, multitasking operating system developed at Bell Labs in the early 1970s. Created by just a handful of programmers, UNIX was designed to be a small, flexible system used exclusively by programmers. Although it has matured considerably over the years, UNIX still betrays its origins by its cryptic command names and its general lack of user-friendliness. This is changing, however, with graphical user interfaces such as MOTIF.

UNIX was one of the first operating systems to be written in a high-level programming language, namely C. This meant that it could run on virtually any computer that had a C compiler. This natural portability combined with its low price made it a popular choice among universities. (It was inexpensive because antitrust regulations prohibited Bell Labs from marketing it as a full-scale product.)

Bell Labs distributed the operating system in its source language form, so anyone who obtained a copy could modify and customize it for his own purposes. By the end of the 1970s, dozens of different versions of UNIX were running at various sites.

After its breakup in 1982, AT&T began to market UNIX in earnest. It also began the long and difficult process of defining a standard version of UNIX. To date, there are two main dialects of UNIX; one produced by AT&T known as System V and one developed at Berkeley University and known as BSD4.x, x being a number from 1 to 3.

Due to its portability, flexibility, and power, UNIX has become the leading operating system for workstations. It is less popular in the personal computer market, where it is known as Xenix or AIX (for PCs) and A/UX operating system (for Macintosh computers). Until recently, most personal computers did not have enough power to take advantage of UNIX. Now UNIX must compete with OS/2 and Windows NT, which offer many of the same features as UNIX while remaining compatible with DOS and Windows.


unpack

To convert a packed file into its original form. A packed file is a file that has been compressed to take up less storage area.


upgrade

A new version of a software or hardware product designed to replace an older version of the same product. Typically, software companies sell upgrades at a discount to prevent users from switching to other products. In most cases, you must prove you own an older version of the product to qualify for the upgrade price. In addition, the installation routines for upgrades often check to make sure that an older version is already installed on your computer; if not, you cannot install the upgrade.

In the 90s, software companies began offering competitive upgrades, which means that you can buy a program at a discount if you can prove that you own a competing program.


upload

To transmit data from a computer to a bulletin board service, mainframe, or network. For example, if you use a personal computer to log on to a network and you want to send files across the network, you must upload the files from your PC to the network.


upper memory area

Same as high memory.


uppercase

Uppercase characters are capital letters; lowercase characters are small letters. For example, box is in lowercase while BOX is in uppercase. The term is a vestige of the days when typesetters kept capital letters in a box above the lowercase letters.

A program that distinguishes between uppercase and lowercase is said to be case sensitive.


UPS

Abbreviation of uninterruptible power supply, a power supply that includes a battery to maintain power in the event of a power outage. Typically, a UPS keeps a computer running for several minutes after a power outage, enabling you to save data that is in RAM and shut down the computer gracefully. Many UPSs now offer a software component that enables you to automate backup and shut down procedures in case there’s a power failure while you’re away from the computer.

There are two basic types of UPS systems: standby power systems (SPSs) and on-line UPS systems. An SPS monitors the power line and switches to battery power as soon as it detects a problem. The switch to battery, however, can require several milliseconds, during which time the computer is not receiving any power.

An on-line UPS avoids these momentary power lapses by constantly providing power from its own inverter, even when the power line is functioning properly. In general, on-line UPSs are much more expensive than SPSs.


upward compatible

Refers to software that runs not only on the computer for which it was designed, but also on newer and more powerful models. For example, a program designed to run on an Intel 386 microprocessor, which also runs on a Pentium, is upward compatible. Upward compatibility is important because it means you can move to a newer, larger, and more sophisticated computer without converting your data.

In contrast to upward compatibility, downward (backward) compatible means that a program runs not only on the computer for which it was designed, but also on smaller and older models. For example, a program designed to run under MS-DOS 6.0, which also works under MS-DOS 5.0, is downward compatible.


URL

Abbreviation of Uniform Resource Locator, the global address of documents and other resources on the Internet.


USENET

A worldwide bulletin board system that can be accessed through the Internet or through many online services. The USENET contains nearly two thousand forums, called newsgroups, that cover every imaginable interest group. It is used daily by millions of people around the world.


user

An individual who uses a computer. This includes expert programmers as well as novices. An end user is any individual who runs an application program.


user group

A group of individuals with common interests in some aspect of computers. Some user groups cover nearly everything with subgroups (called SIGs) for more specialized interests, while others concentrate on a particular area, such as computer graphics, or a particular application.

Nearly every major city in the U.S. has many user groups that meet to share ideas. Joining a local user group is a particularly good way for computer novices to get free expert advice.


user interface

The junction between a user and a computer program. An interface is a set of commands or menus through which a user communicates with a program. A command-driven interface is one in which you enter commands. A menu-driven interface is one in which you select command choices from various menus displayed on the screen.

The user interface is one of the most important parts of any program because it determines how easily you can make the program do what you want. A powerful program with a poorly designed user interface has little value. Graphical user interfaces (GUIs) that use windows, icons, and pop-up menus have become standard on personal computers.


user-friendly

Refers to anything that makes it easier for novices to use a computer. Menu-driven programs, for example, are considered more user-friendly than command-driven systems. Graphical user interfaces (GUIs) are also considered user-friendly. Online help systems are another feature of user-friendly programs.

Although the term user-friendly represents an important concept, it has been so overused that it has become something of a cliché.


username

A name used to gain access to a computer system. Usernames, and often passwords, are required in multi-user systems. In most such systems, users can choose their own usernames and passwords.

Usernames are also required to access some bulletin board and online services.


utility

A program that performs a very specific task, usually related to managing system resources. Operating systems contain a number of utilities for managing disk drives, printers, and other devices.

Utilities differ from applications mostly in terms of size and complexity. For example, word processors, spreadsheet programs, and database applications are considered applications because they are large programs that perform a variety of functions not directly related to managing computer resources.

Utilities are sometimes installed as memory-resident programs. On DOS systems, such utilities are called TSRs.


Uudecode

See under uuencode.


Uuencode

A set of algorithms for converting files into a series of 7-bit ASCII characters that can be transmitted over the Internet. Originally, uuencode stood for Unix-to-Unix encode, but it has since become a universal protocol used to transfer files between different platforms such as Unix, Windows, and Macintosh.  Uuencoding is especially popular for sending e-mail attachments.  Nearly all e-mail applications support uuencoding for sending attachments and uudecoding for receiving attachments.

Another popular encoding algorithm is BinHex, which is often used for transferring Macintosh files, such as PICT graphics files.


V.22

Pronounced V-dot-twenty-two, V.22 is short for the CCITT V.22 communications standard. See under CCITT.


V.22bis

Pronounced V-dot-twenty-two-biss, V.22bis is short for the CCITT V.22bis communications standard. See under CCITT.


V.32

Pronounced V-dot-thirty-two, V.32 is short for the CCITT V.32 communications standard. See under CCITT.


V.34

Pronounced V-dot-thirty-four, V.34 is short for the CCITT V.34 communications standard. See under CCITT.


V.42

Pronounced V-dot-forty-two, V.42 is short for the CCITT V.42 communications standard. See under CCITT.


value-added reseller

See VAR.


vanilla

Without added features. A “vanilla PC,” for example, would be a PC with all standard components.


vaporware

A sarcastic term used to designate software products that have been announced but are not yet available.


VAR

Acronym for value-added reseller. Same as OEM (original equipment manufacturer).


variable

A symbol or name that stands for a value. For example, in the expression

x+y

x and y are variables. Variables can represent numeric values, characters, character strings, or memory addresses.

Variables play an important role in computer programming because they enable programmers to write flexible programs. Rather than entering data directly into a program, a programmer can use variables to represent the data. Then, when the program is executed, the variables are replaced with real data. This makes it possible for the same program to process different sets of data.

Every variable has a name, called the variable name, and a data type. A variable's data type indicates what sort of value the variable represents, such as whether it is an integer, a floating-point number, or a character.

The opposite of a variable is a constant. Constants are values that never change. Because of their inflexibility, constants are used less often than variables in programming.


variable length

Refers to anything whose length can vary. For example, in databases, a variable-length field is a field that does not have a fixed length. Instead, the field length varies depending on what data is stored in it.

Variable-length fields are useful because they save space. Suppose, for example, that you want to define a NAME field. The length of each NAME field will vary according to the data placed in it. For example, John Smith is 10 characters long, but Thomas Horatio Jefferson is 24 characters long. With fixed-length fields, you would need to define each field to be long enough to hold the longest name. This would be a waste of space for records that had short names. With variable-length fields, the NAME field in each record would be just long enough to hold its data.

The opposite of variable length is fixed length.


variable-length record

A record that has at least one variable-length field. The length of the entire record, therefore, varies according to what data is placed in the variable-length field.


VDT

Short for video display terminal. See under monitor.


VDT radiation

The radiation emitted by video display terminals. Like televisions, computer monitors emit various types of radiation. Since the late 1980s, there has been a public debate about whether this radiation poses a health problem. To date, however, there is no conclusive evidence to settle the question once and for all.


vector

(1) In computer programming, a one-dimensional array.

(2) In computer graphics, a line that is defined by its start and end point.


vector font

Same as scalable font.


vector graphics

Same as object-oriented graphics, refers to software and hardware that use geometrical formulas to represent images. The other method for representing graphical images is through bit maps, in which the image is composed of a pattern of dots. This is sometimes called raster graphics. Programs that enable you to create and manipulate vector graphics are called draw programs, whereas programs that manipulated bit-mapped images are called paint programs.

Vector-oriented images are more flexible than bit maps because they can be resized and stretched. In addition, images stored as vectors look better on devices (monitors and printers) with higher resolution, whereas bit-mapped images always appear the same regardless of a device's resolution. Another advantage of vector graphics is that representations of images often require less memory than bit-mapped images do.

Almost all sophisticated graphics systems, including CADD systems and animation software, use vector graphics. In addition, many printers (PostScript printers, for example) use vector graphics. Fonts represented as vectors are called vector fonts, scalable fonts, object-oriented fonts, and outline fonts.

Note that most output devices, including dot-matrix printers, laser printers, and display monitors, are raster devices (plotters are the notable exception). This means that all objects, even vector objects, must be translated into bit maps before being output. The difference between vector graphics and raster graphics, therefore, is that vector graphics are not translated into bit maps until the last possible moment, after all sizes and resolutions have been specified. PostScript printers, for example, have a raster image processor (RIP) that performs the translation within the printer. In their vector form, therefore, graphics representations can potentially be output on any device, with any resolution, and at any size.


vertical frequency

See under refresh.


vertical justification

A feature supported by some word processors and desktop publishing systems in which the system automatically adjusts the vertical space between lines (the leading) so that columns and pages have an even top and bottom margin. This is also called feathering.


vertical refresh rate

See under refresh.


vertical scrolling

See scroll.


very large-scale integration

See VLSI.


VESA

Short for Video Electronics Standards Association, a consortium of video adapter and monitor manufacturers whose goal is to standardize video protocols. VESA has developed a family of video standards that offer greater resolution and more colors than VGA. These standards are known collectively as Super VGA (SVGA).


VESA Local Bus

See VL-Bus.


VGA

Abbreviation of video graphics array, a graphics display system for PCs developed by IBM. VGA has become one of the de facto standards for PCs. In text mode, VGA systems provide a resolution of 720 by 400 pixels. In graphics mode, the resolution is either 640 by 480 (with 16 colors) or 320 by 200 (with 256 colors). The total palette of colors is 262,144.

Unlike earlier graphics standards for PCs—MDA, CGA, and EGA—VGA uses analog signals rather than digital signals. Consequently, a monitor designed for one of the older standards will not be able to use VGA.

Since its introduction in 1987, several other standards have been developed that offer greater resolution and more colors (see SVGA, 8514/A graphics standard, and XGA), but VGA remains the lowest common denominator. All PCs made today support VGA, and possibly some other more advanced standard.


VGA Plus

See under SVGA.


video accelerator

Same as graphics accelerator.


video adapter

A board that plugs into a personal computer to give it display capabilities. The display capabilities of a computer, however, depend on both the logical circuitry (provided in the video adapter) and the display monitor. A monochrome monitor, for example, cannot display colors no matter how powerful the video adapter.

Many different types of video adapters are available for PCs. Most conform to one of the video standards defined by IBM or VESA.

Each adapter offers several different video modes. The two basic categories of video modes are text and graphics. In text mode, a monitor can display only ASCII characters. In graphics mode, a monitor can display any bit-mapped image. Within the text and graphics modes, some monitors also offer a choice of resolutions. At lower resolutions a monitor can display more colors.

Most modern video adapters contain memory, so that the computer's RAM is not used for storing displays. In addition, some adapters have their own graphics coprocessor for performing graphics calculations. These adapters are often called graphics accelerators.

Video adapters are also called video cards, video boards, and video display boards.


video capture

Converting analog video signals, such as those generated by a video camera, into a digital format and then storing the digital video on a computer’s mass storage device. Video capture requires a special video capture card that converts the analog signals into digital form and compresses the data.


video card

Same as video adapter.


video display board

Same as video adapter.


Video Electronics Standards Association

See VESA.


Video for Windows

A format developed by Microsoft Corporation for storing video and audio information. Files in this format have a .AVI extension. AVI files are limited to 320 x 240 resolution, and 15 frames per second, neither of which is adequate for full-screen, full-motion video. However, Video for Windows does not require any special hardware, making it the lowest common denominator for multimedia application. Many multimedia producers use this format because it allows them to sell their products to the largest base of users.

A competing software-only video format is QuickTime. Although QuickTime and Video for Windows are widely used, they may eventually succumb to technologies such as MPEG that use hardware to compress and decompress data.


Video Graphics Array

See VGA.


video mode

The setting of a video adapter. Most video adapters can run in either text mode or graphics mode. In text mode, a monitor can display only ASCII characters. In graphics mode, a monitor can display any bit-mapped image. In addition to the text and graphics modes, some video adapters offer different resolution modes.


video RAM

See VRAM.


video standards

There are a variety of video standards that define the resolution and colors for displays. Support for a graphics standard is determined both by the monitor and by the video adapter. The monitor must be able to show the resolution and colors defined by the standard, and the video adapter must be capable of transmitting the appropriate signals to the monitor.

Listed here, in approximate order of increasing power and sophistication, are the more popular video standards for PCs. Note that many of these numbers represent only the minimums specified in the standards. Many suppliers of video adapters provide greater resolution and more colors. For more information, refer to the entries for the specific graphics systems.


videoconferencing

Conducting a conference between two or more participants at different sites by using computer networks to transmit audio and video data. For example, a point-to-point (two-person) video conferencing system works much like a video telephone. Each participant has a video camera, microphone, and speakers mounted on his or her computer. As the two participants speak to one another, their voices are carried over the network and delivered to the other’s speakers, and whatever images appear in front of the video camera appear in a window on the other participant’s monitor.

Multipoint videoconferencing allows three or more participants to sit in a virtual conference room and communicate as if they were sitting right next to each other. Until the mid 90s, the hardware costs made videoconferencing prohibitively expensive for most organizations, but that situation is changing rapidly. Many analysts believe that videoconferencing will be one of the fastest-growing segments of the computer industry in the latter half of the decade.


view

In database management systems, a view is a particular way of looking at a database. A single database can support numerous different views. Typically, a view arranges the records in some order and makes only certain fields visible. Note that different views do not affect the physical organization of the database.


viewer

A utility program that enables you to read a file in its native format. A Lotus 1-2-3 viewer, for example, enables you to read Lotus 1-2-3 files. Many shell utilities and file managers include viewers so that you can display different types of files.


virtual

Not real. The term virtual is popular among computer scientists and is used in a wide variety of situations. In general, it distinguishes something that is merely conceptual from something that has physical reality. For example, virtual memory refers to an imaginary set of locations, or addresses, where you can store data. It is imaginary in the sense that the memory area is not the same as the real physical memory composed of transistors. The difference is a bit like the difference between an architect's plans for a house and the actual house. A computer scientist might call the plans a virtual house. Another analogy is the difference between the brain and the mind. The mind is a virtual brain. It exists conceptually, but the actual physical matter is the brain.

The opposite of virtual is real, absolute, or physical.


virtual disk

Same as RAM disk.


virtual memory

An imaginary memory area supported by some operating systems (for example, Windows but not DOS) in conjunction with the hardware. You can think of virtual memory as an alternate set of memory addresses. Programs use these virtual addresses rather than real addresses to store instructions and data. When the program is actually executed, the virtual addresses are converted into real memory addresses.

The purpose of virtual memory is to enlarge the address space, the set of addresses a program can utilize. For example, virtual memory might contain twice as many addresses as main memory. A program using all of virtual memory, therefore, would not be able to fit in main memory all at once. Nevertheless, the computer could execute such a program by copying into main memory those portions of the program needed at any given point during execution.

To facilitate copying virtual memory into real memory, the operating system divides virtual memory into pages, each of which contains a fixed number of addresses. Each page is stored on a disk until it is needed. When the page is needed, the operating system copies it from disk to main memory, translating the virtual addresses into real addresses.

The process of translating virtual addresses into real addresses is called mapping. The copying of virtual pages from disk to main memory is known as paging or swapping.


virtual reality

An artificial environment created with computer hardware and software and presented to the user in such a way that it appears and feels like a real environment. To “enter” a virtual reality, a user dons special gloves, earphones, and goggles, all of which receive their input from the computer system. In this way, at least three of the five senses are controlled by the computer. In addition to feeding sensory input to the user, the devices also monitor the user’s actions. The goggles, for example, track how the eyes move and respond accordingly by sending new video input.

To date, virtual reality systems require extremely expensive hardware and software and are confined mostly to research laboratories.


virus

A piece of code that can replicate itself. All computer viruses are manmade. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.

Since 1987, when a virus infected ARPANET, a large network used by the Defense Department and many universities, many antivirus programs have become available. These programs periodically check your computer system for the best-known types of viruses. However, if you receive your software from reliable sources and you are not attached to a network, there is little chance that your system will be infected.

Some people distinguish between general viruses and worms. A worm is a special type of virus that can replicate itself and use memory, but cannot attach itself to other programs.


VL-Bus

Short for VESA Local-Bus, a local bus architecture created by the Video Electronics Standards Association (VESA). Although it was quite popular in PCs made in 1993 and 1994, it has been overshadowed by a competing local bus architecture called PCI.


VLSI

Abbreviation of very large-scale integration, the process of placing thousands (or hundreds of thousands) of electronic components on a single chip. Nearly all modern chips employ VLSI architectures, or ULSI (ultra large scale integration).


voice mail

Refers to e-mail systems that support audio. Users can leave spoken messages for one another and listen to the messages by executing the appropriate command in the e-mail system.


voice recognition

The field of computer science that deals with designing computer systems that can recognize spoken words. Note that voice recognition implies only that the computer can take dictation, not that it understands what is being said. Comprehending human languages falls under a different field of computer science called natural language processing.

A number of voice recognition systems are available on the market. The most powerful can recognize thousands of words. However, they require an extended training session during which the computer system becomes accustomed to a particular voice and accent. Such systems are said to be speaker dependent.

Most systems also require that the speaker speak slowly and distinctly and separate each word with a short pause. These systems are called discrete speech systems. It will be many years before voice recognition systems support continuous speech so that users can speak naturally.

Because of their limitations and high cost, voice recognition systems are used only in a few specialized situations. For example, such systems are useful in instances when the user is unable to use a keyboard to enter data because his or her hands are occupied or disabled. Instead of typing commands, the user can simply speak into a headset.


volatile memory

Memory that loses its contents when the power is turned off. All RAM, for example, is volatile. ROM, on the other hand, is nonvolatile.


volume

A fixed amount of storage on a disk or tape. The term volume is often used as a synonym for the storage medium itself, but it is possible for a single disk to contain more than one volume or for a volume to span more than one disk.


volume label

In DOS systems, the name of a volume (that is, the name of a disk or tape). Specifying a volume label makes it easier to keep track of what data is stored on each medium.


VRAM

Short for video RAM, and pronounced vee-ram. VRAM is special-purpose memory used by video adapters. Unlike conventional RAM, VRAM can be accessed by two different devices simultaneously. This enables a monitor to access the VRAM for screen updates at the same time that a graphics processor provides new data. VRAM yields better graphics performance but is more expensive than normal RAM.


WAIS

Short for Wide Area Information Server, and pronounced ways, a program for finding documents on the Internet. WAIS is rather primitive in its search capabilities.


wait state

A time-out period during which a CPU or bus lies idle. Wait states are sometimes required because different components function at different clock speeds. For example, if the CPU is much faster than the memory chips, it may need to sit idle during some clock cycles so that the memory chips can catch up. Likewise, buses sometimes require wait states if expansion boards run slower than the bus.

A zero wait state microprocessor is one that runs at the maximum speed without any time-outs to compensate for slow memory. Wait states can be avoided by using a variety of techniques, including page-mode memory, interleaved memory, and memory caches.


WAN

See wide-area network.


warm boot

Refers to resetting a computer that is already turned on. Resetting it returns the computer to its initial state, and any data or programs in main memory are erased. A warm boot is sometimes necessary when a program encounters an error from which it cannot recover. On PCs, you can perform a warm boot by pressing the Control, Alt, and Delete keys simultaneously. On Macs, you can perform a warm boot by pressing the Restart button.

A cold boot refers to turning a computer on from an off position.


web page

A document on the World Wide Web. Every web page is identified by a unique URL (Uniform Resource Locator).


web site

A site (location) on the World Wide Web. Each web site contains a home page, which is the first document users see when they enter the site. The site might also contain additional documents and files. Each site is owned and managed by an individual, company or organization.


what-you-see-is-what-you-get

See WYSIWYG.


whitespace

Refers to all characters that appear as blanks on a display screen or printer. This includes the space character, the tab character, and sometimes other special characters that do not have a visual form (for example, the bell character and null character).


Wide Area Information Server

See WAIS.


wide SCSI

See under SCSI.


wide-area network (WAN)

A computer network that spans a relatively large geographical area. Computers connected to a wide-area network are connected through telephone lines or radio waves.


widow

(1) In word processing, the last line of a paragraph that appears as the first line of a page. Widows are considered bad form in page layout, so many word processors allow you to avoid them. When the word processor detects a widow, it can end the page one or more lines early so that at least the last two lines from the paragraph start the next page. Some word processors avoid widows by moving all the lines on the page closer together so that the last line can fit on the same page.

The converse of a widow is an orphan, the first line of a paragraph appearing as the last line of a page.

(2) The last line of a paragraph that is much shorter than all the other lines in the paragraph.


wild card

A special symbol that stands for one or more characters. Many operating systems and applications support wildcards for identifying files and directories. This enables you to select multiple files with a single specification. For example, in DOS and Windows, the asterisk (*) is a wild card that stands for any combination of letters. The file specification

m*

therefore, refers to all files that begin with m. Similarly, the specification

m*.doc

refers to all files that start with m and end with .doc.

Many word processors also support wild cards for performing text searches.


Winchester disk drive

Another term for hard disk drive. The term Winchester comes from an early type of disk drive developed by IBM that stored 30MB (megabytes) and had a 30-millisecond access time; so its inventors called it a Winchester in honor of the .30-caliber rifle of the same name. Although modern disk drives are faster and hold more data, the basic technology is the same, so Winchester has become synonymous with hard.


window

(1) An enclosed, rectangular area on a display screen. Most modern operating systems and applications have graphical user interfaces that let you divide your display into several windows. Within each window, you can run a different program or display different data.

Windows are particularly valuable in multitasking environments, which allow you to execute several programs at once. By dividing your display into windows, you can see the output from all the programs at the same time. To enter input into a program, you simply click on the desired window to make it the foreground process.

Graphical user interfaces, such as the one supported by the Apple Macintosh or Windows, enable you to set the dimensions and position of each window by moving the mouse and clicking appropriate buttons. Windows can be arranged so that they do not overlap (tiled windows) or so they do overlap (overlaid windows). Overlaid windows (also called cascading windows) resemble a stack of pieces of paper lying on top of one another; only the topmost window is displayed in full. You can move a window to the top of the stack by positioning the pointer in the portion of the window that is visible and clicking the mouse buttons. This is known as popping. You can expand a window to fill the entire screen by selecting the window's zoom box.

In addition to moving windows, changing their size, popping and zooming them, you can also replace an entire window with an icon (this is sometimes called minimizing). An icon is a small picture that represents the program running in the window. By converting a window into an icon, you can free up space on the display screen without erasing the window entirely. It is always possible to reconvert the icon into a window whenever you want.

(2) A window can also be a logical view of a file. By moving the window, you can view different portions of the file.


Windows

When spelled with a capital W, Windows is short for Microsoft Windows.


Windows 95

A major release of the Microsoft Windows operating system released in 1995. Windows 95 represents a significant advance over its precursor, Windows 3.1. In addition to sporting a new user interface, Windows 95 also includes a number of important internal improvements. Perhaps most important, it supports 32-bit applications, which means that future applications written specifically for this operating system should run much faster. And although Windows 95 can run older Windows and DOS applications, it has essentially removed DOS as the underlying platform. This has meant removal of many of the old DOS limitations, such as 640K of main memory and 8-character filenames.


Windows Metafile Format

See WMF.


Windows NT

The most advanced version of the Windows operating system. Windows NT is a 32-bit operating system that supports preemptive multitasking

There are actually two versions of Windows NT: Windows NT Server, designed to act as a server in networks, and Windows NT Workstation for stand-alone or client workstations.


Winsock

Short for Windows Socket, WinSock is an Application Programming Interface (API) for developing Windows programs that can communicate with other machines via the TCP/IP protocol. Windows 95 and Windows NT comes with Dynamic Link Library (DLL) called winsock.dll that implements the API and acts as the glue between Windows programs and TCP/IP connections.

In addition to the Microsoft version of winsock.dll, there are other freeware and shareware versions of winsock.dll. However, there is no official standard for the WinSock API, so each implementation differs in minor ways.


wizard

(1) A utility within an application that helps you use the application to perform a particular task. For example, a “letter wizard” within a word processing application would lead you through the steps of producing different types of correspondence.

(2) An outstanding programmer. Also called a super-programmer. Common wisdom holds that one wizard is worth ten average programmers.


WMF

Short for Windows Metafile Format, graphics file format used to exchange graphics information between Microsoft Windows applications. WMF files can hold both vector and bit-mapped images.


Word

When spelled with a capital W, Word refers to Microsoft Word, a powerful word processor.


word

(1) In word processing, any group of characters separated by spaces or punctuation on both sides. Whether it is a real word or not is unimportant to the word processor.

(2) In programming, the natural data size of a computer. The size of a word varies from one computer to another, depending on the CPU. For computers with a 16-bit CPU, a word is 16 bits (2 bytes). On large mainframes, a word can be as long as 64 bits (8 bytes).

Some computers and programming languages distinguish between shortwords and longwords. A shortword is usually 2 bytes long, while a longword is 4 bytes.


word processing

Using a computer to create, edit, and print documents. Of all computer applications, word processing is the most common. To perform word processing, you need a computer, a special program called a word processor, and a printer. A word processor enables you to create a document, store it electronically on a disk, display it on a screen, modify it by entering commands and characters from the keyboard, and print it on a printer.

The great advantage of word processing over using a typewriter is that you can make changes without retyping the entire document. If you make a typing mistake, you simply back up the cursor and correct your mistake. If you want to delete a paragraph, you simply remove it, without leaving a trace. It is equally easy to insert a word, sentence, or paragraph in the middle of a document. Word processors also make it easy to move sections of text from one place to another within a document, or between documents. When you have made all the changes you want, you can send the file to a printer to get a hardcopy.

Word processors vary considerably, but all word processors support the following basic features:

insert text: Allows you to insert text anywhere in the document.

delete text: Allows you to erase characters, words, lines, or pages as easily as you can cross them out on paper.

cut and paste: Allows you to remove (cut) a section of text from one place in a document and insert (paste) it somewhere else.

copy: Allows you to duplicate a section of text.

page size and margins: Allows you to define various page sizes and margins, and the word processor will automatically readjust the text so that it fits.

search and replace: Allows you to direct the word processor to search for a particular word or phrase. You can also direct the word processor to replace one group of characters with another everywhere that the first group appears.

word wrap: The word processor automatically moves to the next line when you have filled one line with text, and it will readjust text if you change the margins.

print: Allows you to send a document to a printer to get hardcopy.

Word processors that support only these features (and maybe a few others) are called text editors. Most word processors, however, support additional features that enable you to manipulate and format documents in more sophisticated ways. These more advanced word processors are sometimes called full-featured word processors. Full-featured word processors usually support the following features:

file management: Many word processors contain file management capabilities that allow you to create, delete, move, and search for files.

font specifications: Allows you to change fonts within a document. For example, you can specify bold, italics, and underlining. Most word processors also let you change the font size and even the typeface.

footnotes and cross-references: Automates the numbering and placement of footnotes and enables you to easily cross-reference other sections of the document.

graphics: Allows you to embed illustrations and graphs into a document. Some word processors let you create the illustrations within the word processor; others let you insert an illustration produced by a different program.

headers, footers, and page numbering: Allows you to specify customized headers and footers that the word processor will put at the top and bottom of every page. The word processor automatically keeps track of page numbers so that the correct number appears on each page.

layout: Allows you to specify different margins within a single document and to specify various methods for indenting paragraphs.

macros: A macro is a character or word that represents a series of keystrokes. The keystrokes can represent text or commands. The ability to define macros allows you to save yourself a lot of time by replacing common combinations of keystrokes.

merges: Allows you to merge text from one file into another file. This is particularly useful for generating many files that have the same format but different data. Generating mailing labels is the classic example of using merges.

spell checker: A utility that allows you to check the spelling of words. It will highlight any words that it does not recognize.

tables of contents and indexes: Allows you to automatically create a table of contents and index based on special codes that you insert in the document.

thesaurus: A built-in thesaurus that allows you to search for synonyms without leaving the word processor.

windows: Allows you to edit two or more documents at the same time. Each document appears in a separate window. This is particularly valuable when working on a large project that consists of several different files.

WYSIWYG (what you see is what you get):  With WYSIWYG, a document appears on the display screen exactly as it will look when printed.

The line dividing word processors from desktop publishing systems is constantly shifting. In general, though, desktop publishing applications support finer control over layout, and more support for full-color documents.


word processor

A program or computer that enables you to perform word processing functions.


word wrap

In word processing, a feature that causes the word processor to force all text to fit within the defined margins. When you fill one line with text, the word processor automatically jumps to the next line so that you are not required to keep track of line lengths and to press the Return key after each line. The word processor divides lines in such a way that a word is never split between two lines (unless the word processor supports hyphenation).

Word wrap also occurs if you change the margins. In this case, the word processor readjusts all the text so that it fits within the new margins.

Note that word wrap inserts a soft return at the end of each line, not a hard return. Soft returns are invisible codes that the word processor utilizes. Hard returns are real characters inserted into the document.

Some word processors allow you to turn off the word-wrap feature. This is useful for writing programs and other types of formatted text where you want complete control over new lines.


WordPerfect

One of the most popular word processors for PCs and Apple Macintoshes.


workgroup computing

A workgroup is a collection of individuals working together on a task. Workgroup computing occurs when all the individuals have computers connected to a network that allows them to send e-mail to one another, share data files, and schedule meetings.


workgroup productivity package

Software packages that include e-mail, calendar programs, scheduling programs, and other utilities that promote communication between users on a local-area network.


working directory

The directory in which you are currently working. Pathnames that do not start with the root directory are assumed by the operating system to start from the working directory.


worksheet

Same as spreadsheet.


workstation

(1) A type of computer used for engineering applications (CAD/CAM), desktop publishing, software development, and other types of applications that require a moderate amount of computing power and relatively high quality graphics capabilities.

Workstations generally come with a large, high-resolution graphics screen, at least 16MB (megabytes) of RAM, built-in network support, and a graphical user interface. Most workstations also have a mass storage device such as a disk drive, but a special type of workstation, called a diskless workstation, comes without a disk drive. The most common operating system for workstations is UNIX.

In terms of computing power, workstations lie between personal computers and minicomputers, although the line is fuzzy on both ends. High-end personal computers such as the PowerMac are equivalent to low-end workstations. And high-end workstations are equivalent to minicomputers.

Like personal computers, most workstations are single-user computers. However, workstations are typically linked together to form a local-area network, although they can also be used as stand-alone systems.

The leading manufacturers of workstations are Sun Computer, Hewlett-Packard Corporation, and Digital Electronics Corporation.

(2) In networking, workstation refers to any computer connected to a local-area network. It could be a workstation or a personal computer.


World Wide Web

A system of Internet servers that support specially formatted documents. The documents are formatted in a language called HTML (HyperText Markup Language) that supports links to other documents, as well as graphics, audio, and video files. This means you can jump from one document to another simply by clicking on hot spots. Not all Internet servers are part of the World Wide Web.

There are several applications that make it easy to access the World Wide Web, two of the most popular being Mosaic and Netscape.


WORM (write-once, read many)

Refers to an optical disk technology that allows you to write data onto a disk just once. After that, the data is permanent and can be read any number of times. A single WORM disk can store from 600MB (megabytes) (megabytes) to over 3GB (gigabytes) of data.

Unlike CD-ROMs, there is no single standard for WORM disks, which means that they can only be read by the same type of drive that wrote them. This has hampered their acceptance, although they have found a niche market as an archival media.


write

To copy data from main memory to a storage device, such as a disk.


write once/read many

See WORM.


write-protect

To mark a file or disk so that its contents cannot be modified or deleted. When you want to make sure that neither you nor another user can destroy data, you can write-protect it. Many operating systems include a command to write-protect files. You can also write-protect 5¼-inch floppy disks by covering the write-protect notch with tape. 3½-inch floppy diskettes have a small switch that you can set to turn on write-protection .

Write-protected files and media can only be read; you cannot write to them, edit them, append data to them, or delete them.


WWW

See World Wide Web.


WYSIWYG

Pronounced wizzy-wig, stands for what you see is what you get. A WYSIWYG is a word processor that enables you to see on the display screen exactly what the text will look like when printed. This differs from other word processors, which are incapable of displaying different fonts and graphics on the display screen even though the formatting codes have been inserted into the file. WYSIWYGs are especially popular for desktop publishing.

Note that the WYSIWYGness of an application is relative. Originally, WYSIWYG referred to any word processor that could accurately show line breaks on the display screen. Later WYSIWYGs had to be able to show different font sizes, even if the screen display was limited to one typeface. Now, a word processor must be able to display many different typefaces to be considered a WYSIWYG.

Still, some WYSIWYGs are more WYSIWYG than others. For example, many desktop publishing systems print text using outline fonts (PostScript fonts, for example). Many of these systems, however, use corresponding bit-mapped fonts to display documents on a monitor. What you see on the display screen, therefore, is not exactly what you see when you print out the document. In addition, standard laser printers have a resolution of at least 300 dpi, whereas even the best graphics monitors have resolutions of only 100 dpi. Graphics and text, therefore, always look sharper when printed than they do on the display screen. And colors often appear differently on a monitor than they do when printed out.


WYSIWYP

Short for What You See Is What You Print, and pronounced wizzy-whip, refers to the ability of a computer system to print colors exactly as they appear on a monitor. WYSIWYP printing requires  a special program, called a color management system (CMS) to calibrate the monitor and printer.


x-height

In typography, the height of a lowercase x in a specific font. This is also called the body height, as it represents the height of the lowercase character’s body, excluding ascenders and descenders.


X-Windows

A windowing and graphics system developed at the Massachusetts Institute of Technology (MIT). MIT has placed the X-Windows source code in the public domain, making it a particularly attractive system for UNIX vendors. Almost all UNIX graphical interfaces, including Motif and OpenLook, are based on X-Windows.


X.25

See under CCITT.


X.400

See under CCITT.


X.500

See under CCITT.


Xenix

A version of UNIX that runs on PCs. Xenix was developed by Microsoft Corporation and is compatible with AT&T's System V definition.


XGA

Short for extended graphics array, a high-resolution graphics standard introduced by IBM in 1990. XGA was designed to replace the older 8514/A video standard. It provides the same resolutions (640 by 480 or 1024 by 768 pixels), but supports more simultaneous colors (65 thousand compared to 8514/A’s 256 colors). In addition, XGA allows monitors to be non-interlaced.


Xmodem

Originally developed in 1977 by Ward Christiansen, Xmodem is one of the most popular file-transfer protocols. Although Xmodem is a relatively simple protocol, it is fairly effective at detecting errors. It works by sending blocks of data together with a checksum and then waiting for acknowledgment of the block's receipt. The waiting slows down the rate of data transmission considerably, but it ensures accurate transmission.

Xmodem can be implemented either in software or in hardware. Many modems, and almost all communications software packages, support Xmodem. However, it is useful only at relatively slow data transmission speeds (less than 4,800 bps).

Enhanced versions of Xmodem that work at higher transmission speeds are known as Ymodem and Zmodem.


XMS

Stands for Extended Memory Specification, a procedure developed jointly by AST Research, Intel Corporation, Lotus Development, and Microsoft Corporation for using extended memory and DOS's high memory area, a 64K block just above 1MB.


XOR operator

Known as the exclusive OR operator, a Boolean operator that returns a value of TRUE only if its two operands have different values.


Ymodem

An asynchronous communications protocol designed by Chuck Forsberg that extends Xmodem by increasing the transfer block size and by supporting batch file transfers. This enables you to specify a list of files and send them all at one time. With Xmodem, you can send only one file at a time.


Zero Insertion Force (ZIF) socket

A chip socket that allows you to insert and remove a chip without special tools.


zero wait state

Refers to microprocessors that have no wait states; that is, they run at their maximum speed without waiting for slower memory chips.


ZIF socket

See Zero Insertion Force (ZIF) socket.


ZIP

A popular data compression format for PCs. The actual utilities for compressing and expanding files according to the ZIP format are called PKZIP and PKUNZIP, respectively. Files that have been compressed with PKZIP usually end with a .ZIP extension.

A special kind of zipped file is a self-extracting file, which ends with a .EXE extension. You can unzip a self-extracting file by simply executing it.


Zmodem

An asynchronous communications protocol that provides faster data transfer rates and better error detection than Xmodem. In particular, Zmodem supports larger block sizes and enables the transfer to resume where it left off following a communications failure.


zoom

In graphical user interfaces, to make a window  larger. Typically, there is a zoom box in one  corner of the window. When you select the zoom box the first time, the  system expands the window to fill the entire screen. (This is sometimes called maximizing.) When you select it again, the window shrinks to its original size. (This is sometimes called restoring.)

Many applications also provide a zoom feature, which enlarges the view of an object enabling you to see more detail.


Sail the Web


No Cross References

There are no cross references for this term.


Licensing Information

This product is freeware. You may use it and distribute it for free. However, you may not sell it nor bundle it with another product without Sandy Bay Software’s express consent. For licensing information, send mail to license@sandybay.com.


Legal Stuff

All definitions, figures, tables, and descriptions of Web sites are copyrighted by Sandy Bay Software, Inc. You may not use them in any other document or product without Sandy Bay Software’s express permission.

While every effort has been made to ensure that the definitions are accurate, the dictionary is supplied as is. Sandy Bay Software disclaims all warranties, expressed or implied, including, without limitation, the warranties of merchantability and of fitness for any purpose. Sandy Bay Software assumes no liability for damages, direct or consequential, which may result from the use of this product.


Instructions

The PC Webopaedia comes in Windows help file format, so if you are an experienced Windows 95 or NT user, it should look familiar to you. If you're new to Windows, select the Help on Help link below to get basic information. The other links provide detailed information about how to use the PC Webopaedia.

•	Help on Help - Basic information about Windows 95 help files.

•	The Windows - Descriptions of the two windows.

•	Finding Information - How to search for information.

•	Following Links - How to follow links to jump from one term to another.

•	Updates and Web Links - How to get the most up-to-date definition and additional information about personal computers from the World Wide Web.


The Windows

The PC Webopaedia consists of two windows:

•	Search Window

•	Definition Window


Search Dialog
Search Window

The Search Window provides a variety of ways to search for terms. To open the window, press the Search button. There are three main ways to find information:

•	Contents: Shows terms organized hierarchically. This view also shows new terms added with the last update.

•	Index: Lists all terms alphabetically. As you type in a term, the list will automatically scroll to the closest matching entry.

•	Find: Enables you to search for particular words or phrases in the entire Webopaedia. For example, if you enter "Macintosh", it will list all terms whose definitions or URL descriptions include "Macintosh".

Click on a tab for more information about specific search method.


Index Tab

The Index tab provides an index of the Webopaedia. As you type characters, the index list will scroll to entries that start with the characters you have entered. To see a list of topics for a particular index term, double-click the term or highlight it and then press the Display button. If there's only one topic for the term, it will be immediately displayed. If there are multiple topics for the term, a new box will appear listing all the topics. Double-click the one you want or highlight it and then press the Display button.


Find Tab

The Find tab enables you to search through the Webopaedia and find all topics containing a word or phrase. If you are using the Webopaedia for the first time, or if you have just received an update, a Find Setup Wizard will appear which will lead you through the steps to creating the full-text index. Once the index has been created, you can type in any word or phrase, and you will see a list of all topics containing the word(s) you entered. To go to a particular topic that is listed, double-click the topic or highlight it and then press the Display button.


Contents Tab

The Contents tab provides a hierarchical view of the Webopaedia. The Webopaedia is divided into two books:

•	Getting Started: Contains topics describing how to use the Webopaedia.

•	Categories: Lists all topics organized by category.

To see the contents of a book, double-click it. This will expand it. There may be additional books within it, or it may contain topics. To go to a particular topic, double-click it.


Updates and Web Links

Because computer terminology changes so fast, the PC Webopaedia comes with a built-in update mechanism. In the upper righthand corner of each definition is a Web icon:

Clicking on this icon will bring you to term’s corresponding PC Webopaedia Web page. Here, you’ll find not only the last version of the definition but also links to other Web pages that contain additional information about the term.

To take advantage of this feature, you need a Netscape, Microsoft or Mosaic browser and Internet access.


Definitions Window
Definition Window

The definition window is where definitions for terms appear. Click on an area to find more information.


This is where the definition appears. Words and phrases in green are pop-up links to other definitions. In addition, there are hidden links. As you move the mouse pointer over a definition, it will turn into a hand whenever it is over a word or phrase that is defined. To see the definition, just click the mouse button.


Clicking on this icon displays the Web links for the term displayed in the Definition window.


Clicking the See Also hotspot displays a list of all terms related to the one in the Definition window.


This is the term whose definition is being displayed.


Some definitions have a figure or table associated with them. Click on the icon to see the graphic.


Following Links

This is a hypertext system, which means that each page contains links to other pages. There are three basic types of links:

•	Visible Pop-ups: Phrases that have a dotted underline beneath them, like this, are pop-ups. Click on them to get additional information.

•	Hidden Pop-ups: There are lots of invisible hot spots in this help file. Pass the mouse pointer over a definition; when it turns into a hand, click to see a pop-up definition. Try it with this sentence.

•	Jumps: Clicking on an underlined phrase, like this one, brings up a new screen of information.


Jump Example

To go back to the previous screen, click here or press the Back button.


Visible Pop-Up

This is an example of a visible pop-up link.


Invisible Pop-Up

This is an example of an invisible pop-up link.


No Refs

No See Also references for this term.


Figure: addresses


Figure: algorithm


Figure: analog vs. digital


Figure: applications vs. systems software


Figure: asynchronous vs. synchronous communications


Figure: bar chart


Figure: Bezier curve


Figure: bit map


Figure: cache


Figure: CAD application


Figure: chips


Figure: collapsed and expanded views


Figure: column graph


Figure: compilation process


Figure: computer


Figure: connectors


Figure: CRT


Figure: database


Figure: dialog box


Figure: dingbats


Figure: dip switches


Figure: directory tree


Figure: dithering


Figure: device driver


Figure: Dvorak keyboard


Figure: fiber optics


Figure: fills


Figure: floppy disks


Figure: fonts


Figure: Fractal


Figure: greeking


Figure: hierarchies


Figure: interleaving


Figure: italic


Figure: joystick


Figure: jumper


Figure: kerning


Figure: keyboards


Figure: landscape vs. portrait orientation


Figure: laptop computer


Figure: light pen


Figure: line graph


Figure: Macintosh


Figure: mail merge


Figure: maximize and minimize buttons


Figure: menu bar


Figure: modem


Figure: mouse


Figure: numeric keypad


Figure: operating system


Figure: optical scanner


Figure: pathhnames


Figure: pie chart


Figure: pipe


Figure: plotter


Figure: pointers


Figure: polyline


Figure: printed circuit board


Figure: programming languages


Figure: proportional pitch font


Figure: random access


Figure: scroll bar


Figure: sector


Figure: template


Figure: text wrap


Figure: token-ring network


Figure: topologies


Figure: tower model


Figure: trackball


Figure: tractor feed vs. friction feed


Figure: tree structure


Figure: typeface


Figure: virtual memory


Figures
Addresses

Algorithm

Analog vs. Digital

Applications vs. Systems Software

Asynchronous vs. Synchronous Communications

Bar Chart

Bezier Curve

Bit Map

Cache

CAD Application

Chips

Collapsed and Expanded Views

Column Graph

Compilation Process

Computer

Connectors

CRT

Database

Dialog Box

Dingbats

Dip Switches

Directory Tree

Dithering

Device Driver

Dvorak Keyboard

Fiber Optics

Fills

Floppy Disks

Fonts

Fractal

Greeking

Hierarchies

Interleaving

Italic

Joystick

Jumper

Kerning

Keyboards

Landscape vs. Portrait Orientation

Laptop Computer

Light Pen

Line Graph

Macintosh

Mail Merge

Maximize and Minimize Buttons

Menu Bar

Modem

Mouse

Numeric Keypad

Operating System

Optical Scanner

Pathhnames

Pie Chart

Pipe

Plotter

Pointers

Polyline

Printed Circuit Board

Programming Languages

Proportional Pitch Font

Random Access

Scroll Bar

Sector

Template

Text Wrap

Token-Ring Network

Topologies

Tower Model

Trackball

Tractor Feed vs. Friction Feed

Tree Structure

Typeface

Virtual Memory


artificial intelligence

The branch of computer science concerned with making computers behave like humans. The term was coined in 1956 by John McCarthy at the Massachusetts Institute of Technology. Artificial intelligence includes

games playing: programming computers to play games such as chess and checkers

expert systems: programming computers to make decisions in real-life situations (for example, some expert systems help doctors diagnose diseases based on symptoms)

natural language: programming computers to understand natural human languages

neural networks: Systems that simulate intelligence by attempting to reproduce the types of physical connections that occur in animal brains

robotics: programming computers to see and hear and react to other sensory stimuli

Currently, no computers exhibit full artificial intelligence (that is, are able to simulate human behavior). The greatest advances have occurred in the field of games playing. The best computer chess programs are now capable of beating most humans, although they still lose to grand masters.

In the area of robotics, computers are now widely used in assembly plants, but they are capable only of very limited tasks. Robots have great difficulty identifying objects based on appearance or feel, and they still move and handle objects clumsily.

Natural-language processing offers the greatest potential rewards because it would allow people to interact with computers without needing any specialized knowledge. You could simply walk up to a computer and talk to it. Unfortunately, programming computers to understand natural languages has proved to be more difficult than originally thought. Some rudimentary translation systems that translate from one human language to another are in existence, but they are not nearly as good as human translators. There are also voice recognition systems that can convert spoken sounds into written words, but they do not understand what they are writing; they simply take dictation. Even these systems are quite limited¾you must speak slowly and distinctly.

In the early 1980s, expert systems were believed to represent the future of artificial intelligence and of computers in general. To date, however, they have not lived up to expectations. Many expert systems help human experts in such fields as medicine and engineering, but they are very expensive to produce and are helpful only in special situations.

Today, the hottest area of artificial intelligence is neural networks, which are proving successful in a number of disciplines such as voice recognition and natural-language processing.

There are several programming languages that are known as AI languages because they are used almost exclusively for AI applications. The two most common are LISP and PROLOG.

⇒	See also expert system; LISP; natural language; neural network; robotics; voice recognition.


binary

Pertaining to a number system that has just two unique digits. For most purposes, we use the decimal number system, which has ten unique digits, 0 through 9. All other numbers are then formed by combining these ten digits. Computers are based on the binary numbering system, which consists of just two unique numbers, 0 and 1. All operations that are possible in the decimal system (addition, subtraction, multiplication, division) are equally possible in the binary system.

We use the decimal system in everyday life because it seems more natural (we have ten fingers and ten toes). For the computer, the binary system is more natural because of its electrical nature (charged versus uncharged).

In the decimal system, each digit position represents a value of 10 to the position's power. For example, the number 345 means:

3	three 100s (102)

plus

4	four 10s (101)

plus

5	five 1s (100)

In the binary system, each digit position represents a power of 2. For example, the binary number 1011 equals:

1	one 8 (23)

plus

0	zero 4s (22)

plus

1	one 2 (21)

plus

1	one 1 (20)

So a binary 1011 equals a decimal 11. (See [image] for binary and decimal equivalents.)

Because computers use the binary number system, powers of 2 play an important role. This is why everything in computers seems to come in 8s (23), 64s (26), 128s (27), and 256s (28).

Programmers also use the octal (8 numbers) and hexadecimal (16 numbers) number systems because they map nicely onto the binary system. Each octal digit represents exactly three binary digits, and each hexadecimal digit represents four binary digits.

⇒	See also decimal; hexadecimal; octal.


communications software

Software that makes it possible to send and receive data over telephone lines through modems. The following features differentiate various communications software packages:

maximum bps rate: The software package should be able to transmit data as fast as your modem. Maximum bps rates for communications packages vary between 9,600 and 57,600 bps.

automatic queue and redial: This is a useful feature if you use your modem to access a service that is frequently busy, such as a bulletin board system (BBS) . When you enter the telephone number in a queue, the communications software will keep redialing the number until it gets through. This feature can also be implemented by the modem itself rather than by the software.

macros: The ability to create macros is very important because you often go through the same steps every time you make a connection. By storing the connection sequence in a macro, you can perform the entire process with a single keystroke.

file transfer protocols: File transfer protocols enable you to transmit ASCII or binary files over a telephone line. The more protocols the package supports, the better. At the very least, it should support Xmodem and Kermit. For high-speed communication, you may require additional protocols, such as Zmodem.

script language: A script is like a program or batch file. It is a file of commands that can be executed without your interaction. The ability to write scripts is useful if you need to log on to services and transfer files while away from your computer.

remote: Packages that support a remote option enable your computer to accept calls while you are not there. This feature is also called auto-answer.

spooling: Packages that support spooling enable you to run another program while files are being transferred in the background. This is sometimes called background processing.

terminal emulation drivers: This is important if you plan to log on to a mainframe from your PC. Most mainframes require that the PC emulate a particular type of terminal. The more terminal emulation drivers a package has, the more mainframes you can log on to. Most packages support TTY emulation and emulate one or more DEC terminals (such as the VT52, VT100/102, or VT220).

In addition to these features, some communications packages offer more advanced programming capabilities that enable you to customize the interface using windows.

⇒	See also auto-answer; batch file; bulletin board system; communications protocol; editor; emulation; Kermit; log on; macro; mainframe; modem; multitasking; queue; script; spooling; terminal; window; word wrap; Xmodem; Ymodem; Zmodem.


computer

A programmable machine. The two principal characteristics of a computer are:

•	It responds to a specific set of instructions in a well-defined manner.

•	It can execute a prerecorded list of instructions (a program).

Modern computers ( [image]) are electronic and digital. The actual machinery—wires, transistors, and circuits—is called hardware; the instructions and data are called software.

All general-purpose computers require the following hardware components:

memory: Enables a computer to store, at least temporarily, data and programs.

mass storage device: Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.

input device: Usually a keyboard or mouse, the input device is the conduit through which data and instructions enter a computer.

output device: A display screen, printer, or other device that lets you see what the computer has accomplished.

central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions.

In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.

Computers can be classified by size and power as follows:

personal computer: A small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.

workstation: A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.

minicomputer: A multi-user computer capable of supporting from 10 to hundreds of users simultaneously.

mainframe: A powerful multi-user computer capable of supporting many hundreds of users simultaneously.

supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second.

⇒	See also CPU; hardware; mainframe; microprocessor; minicomputer; personal computer; software; supercomputer; workstation.


fax machine

Abbreviation of facsimile machine, a fax machine is a device that can send or receive pictures and text over a telephone line. Fax machines work by digitizing an image—dividing it into a grid of dots. Each dot is either on or off, depending on whether it is black or white. Electronically, each dot is represented by a bit that has a value of either 0 (off) or 1 (on). In this way, the fax machine translates a picture into a series of zeros and ones (called a bit map) that can be transmitted like normal computer data. On the receiving side, a fax machine reads the incoming data, translates the zeros and ones back into dots, and reprints the picture.

The idea of fax machines has been around since 1842, when Alexander Bain invented a machine capable of receiving signals from a telegraph wire and translating them into images on paper. In 1850, a London inventor named F. C. Blakewell received a patent for a similar machine, which he called a copying telegraph.

But while the idea of fax machines has existed since the 1800s, fax machines did not become popular until the mid 1980s. The spark igniting the fax revolution was the adoption in 1983 of a standard protocol for sending faxes at rates of 9,600 bps. The standard was created by the CCITT standards organization and is known as the Group 3 standard. Now, faxes are commonplace in offices of all sizes. They provide an inexpensive, fast, and reliable method for transmitting correspondence, contracts, résumés, handwritten notes, and illustrations.

A fax machine consists of an optical scanner for digitizing images on paper, a printer for printing incoming fax messages, and a telephone for making the connection. The optical scanner generally does not offer the same quality of resolution as stand-alone scanners. Most printers on fax machines are thermal, which means they require a special kind of paper.

All fax machines conform to the CCITT Group 3 protocol. (There is a new protocol called Group 4, but it requires ISDN lines.) The Group 3 protocol supports two classes of resolution: 203 by 98 dpi and 203 by 196 dpi. The protocol also specifies a data-compression technique and a maximum transmission speed of 9,600 bps.

Some of the features that differentiate one fax machine from another include the following:

speed: fax machines transmit data at different rates, from 4,800 bps to 28,800 bps. A 9,600-bps fax machine typically requires 10 to 20 seconds to transmit one page.

printer type: Most fax machines use a thermal printer that requires special paper that tends to turn yellow or brown after a period. More expensive fax machines have printers that can print on regular bond paper.

paper size: The thermal paper used in most fax machines comes in two basic sizes: 8.5-inches wide and 10.1-inches wide. Some machines accept only the narrow-sized paper.

paper cutter: Most fax machines include a paper cutter because the thermal paper that most fax machines use comes in rolls. The least expensive models and portable faxes, however, may not include a paper cutter.

paper feed: Most fax machines have paper feeds so that you can send multiple-page documents without manually feeding each page into the machine.

autodialing: fax machines come with a variety of dialing features. Some enable you to program the fax to send a document at a future time so that you can take advantage of the lowest telephone rates.

As an alternative to stand-alone fax machines, you can also put together a fax system by purchasing separately a fax modem and an optical scanner. You may not even need the optical scanner if the documents you want to send are already in electronic form.

⇒	See also bps; digitize; fax modem; optical scanner; thermal printer.


font

A design for a set of characters ( [image]). A font is the combination of typeface and other qualities, such as size, pitch, and spacing. For example, Times Roman is a typeface that defines the shape of each character. Within Times Roman, however, there are many fonts to choose from—different sizes, italic, bold, and so on. (The term font is often used incorrectly as a synonym for typeface.)

The height of characters in a font is measured in points, each point being approximately 1/72 inch. For example, the text in this book is printed with 9-point type. The width is measured by pitch, which refers to how many characters can fit in an inch. Common pitch values are 10 and 12. A font is said to be fixed pitch if every character has the same width. If the widths vary depending on the shape of the character, it is called a proportional font.

Most applications that support text enable you to choose from among many fonts. Laser, ink-jet, and dot-matrix printers offer the widest selection of fonts. These printers support a certain set of built-in fonts, but you can expand this set by loading different fonts from software (soft fonts) or from font cartridges.

Computers and devices use two methods to represent fonts. In a bit-mapped font, every character is represented by an arrangement of dots. To print a bit-mapped character, a printer simply locates the character's bit-mapped representation stored in memory and prints the corresponding dots. Each different font, even when the typeface is the same, requires a different set of bit maps.

The other method utilizes a vector graphics system to define fonts. In vector graphics systems, the shape or outline of each character is defined geometrically. The typeface can be displayed in any size, so a single font description really represents innumerable fonts. For this reason, vector fonts are called scalable fonts—they can be any size (scale). Other terms for vector fonts are object-oriented fonts or outline fonts. The most widely used scalable-font systems are PostScript and TrueType.

Aside from the scalability of vector fonts, their other main advantage over bit-mapped fonts is that they make the most of high-resolution devices. Bit-mapped fonts look almost the same whether printed on a 300-dpi printer or a 1,200-dpi printer. Vector fonts look better, the higher the resolution.

Despite the advantages of vector fonts, bit-mapped fonts are still widely used. One reason for this is that small vector fonts do not look very good on low-resolution devices, such as display monitors (which are low-resolution when compared with laser printers). Many computer systems, therefore, use bit-mapped fonts for screen displays. These are sometimes called screen fonts. In addition, some professionals prefer to use bit-mapped fonts on high-resolution printers because characters can be individually tailored to the printing device.

An additional drawback of vector fonts is that every character must be generated as it is needed. This is a computation-intensive process that requires a powerful microprocessor to make it acceptably fast.

⇒	See also bit-mapped graphics; fixed pitch; font cartridge; Page Description Language; pitch; point; PostScript; proportional pitch; scalable font; soft font; TrueType; typeface; vector graphics.


graphical user interface (GUI)

A program interface that takes advantage of the computer'sgraphics capabilities to make the program easier to use. Well-designed graphical user interfaces can free the user from learning complex command languages. On the other hand, many users find that they work more effectively with a command-driven interface, especially if they already know the command language.

Graphical user interfaces, such as Microsoft Windows and the one used by the Apple Macintosh, feature the following basic components:

pointer: A symbol that appears on the display screen and that you move to select objects and commands. Usually, the pointer appears as a small angled arrow. Text-processing applications, however, use an I-beam pointer that is shaped like a capital I.

pointing device: A device, such as a mouse or trackball, that enables you to select objects on the display screen.

icons: Small pictures that represent commands, files, or windows. By moving the pointer to the icon and pressing a mouse button, you can execute a command or convert the icon into a window. You can also move the icons around the display screen as if they were real objects on your desk.

desktop: The area on the display screen where icons are grouped is often referred to as the desktop because the icons are intended to represent real objects on a real desktop.

windows: You can divide the screen into different areas. In each window, you can run a different program or display a different file. You can move windows around the display screen, and change their shape and size at will.

menus: Most graphical user interfaces let you execute commands by selecting a choice from a menu.

The first graphical user interface was designed by Xerox Corporation's Palo Alto Research Center in the 1970s, but it was not until the 1980s and the emergence of the Apple Macintosh that graphical user interfaces became popular. One reason for their slow acceptance was the fact that they require considerable CPU power and a high-quality monitor, which until recently were prohibitively expensive.

In addition to their visual components, graphical user interfaces also make it easier to move data from one application to another. A true GUI includes standard formats for representing text and graphics. Because the formats are well-defined, different programs that run under a common GUI can share data. This makes it possible, for example, to copy a graph created by a spreadsheet program into a document created by a word processor.

Many DOS programs include some features of GUIs, such as menus, but are not graphics based. Such interfaces are sometimes called graphical character-based user interfaces to distinguish them from true GUIs.

⇒	See also character based; desktop; icon; Macintosh computer; Microsoft Windows; pointer; pointing device; user interface.


graphics

Pertains to any computerdevice or program that makes a computercapable of displaying and manipulating pictures. For example, laser printers and plotters are graphics devices because they permit the computerto output pictures. A graphics monitor is a display monitor that can display pictures. A graphics board (or graphics card) is a printed circuit board that, when installed in a computer, permits the computerto display pictures.

Many software applications include graphics components. Such programs are said to support graphics. For example, certain word processors support graphics because they let you draw or import pictures. All CAD/CAM systems support graphics. Some database management systems and spreadsheet programs support graphics because they let you display data in the form of graphs and charts. Such applications are often referred to as business graphics.

The following are also considered graphics applications:

paint programs: Allow you to create rough freehand drawings. The images are stored as bit maps and can easily be edited.

illustration/design programs: Supports more advanced features than paint programs, particularly for drawing curved lines. The images are usually stored in vector-based formats. Illustration/design programs are often called draw programs.

presentation graphics software: Lets you create bar charts, pie charts, graphics, and other types of images for slide shows and reports. The charts can be based on data imported from spreadsheet applications.

animation software: Enables you to chain and sequence a series of images to simulate movement. Each image is like a frame in a movie.

CAD software: Enables architects and engineers to draft designs.

desktop publishing: Provides a full set of word-processing features as well as fine control over placement of text and graphics, so that you can create newsletters, advertisements, books, and other types of documents.

In general, applications that support graphics require a powerful CPU and a large amount of memory. Many graphics applications¾for example, computeranimation systems¾require more computing power than is available on personal computers and will run only on powerful workstations or specially designed graphics computers. This is true of all three-dimensional computer graphics applications.

In addition to the CPU and memory, graphics software requires a graphics monitor and support for one of the many graphics standards. Most PC programs, for instance, require VGA graphics. If your computerdoes not have built-in support for a specific graphics system, you can insert a video adapter card.

The quality of most graphics devices is determined by their resolution¾how many points per square inch they can represent¾and their color capabilities.

⇒	See also bit map; bit-mapped graphics; CAD; CAD/CAM; character based; clip art; CPU; desktop publishing; display screen; laser printer; monitor; Microsoft Windows; personal computer; plotter; presentation graphics;  resolution; spreadsheet; vector graphics; video adapter; workstation.


keyboard

The set of typewriter-like keys that enables you to enter data into a computer. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys. The keys on computer keyboards are often classified as follows:

alphanumeric keys—letters and numbers

punctuation keys—comma, period, semicolon, and so on.

special keys—function keys, control keys, arrow keys, Caps Lock key, and so on.

The standard layout of letters, numbers, and punctuation is known as a QWERTY keyboard because the first five keys on the top row of letters spell QWERTY. The QWERTY keyboard was designed in the 1800s for mechanical typewriters and was actually designed to slow typists down to avoid jamming the keys. Another keyboard design, which has letters positioned for speed typing, is the Dvorak keyboard.

There is no standard computer keyboard, although many manufacturers imitate the keyboards of PCs. There are actually three different PC keyboards: the original PC keyboard, with 84 keys; the AT keyboard, also with 84 keys; and the enhanced keyboard, with 101 keys. They are shown in [image]. The three differ somewhat in the placement of function keys, the Control key, the Return key, and the Shift keys. Despite the placement differences, almost all computer keyboards contain the special-purpose keys shown in [image] 9.

In addition to these keys, IBM keyboards contain the following keys: Page Up, Page Down, Home, End, Insert, Pause, Num Lock, Scroll Lock, Break, Caps Lock, Print Screen.

There are several different types of keyboards for the Apple Macintosh. All of them are called ADB keyboards because they connect to the Apple Desktop bus (ADB). The two main varieties of Macintosh keyboards are the standard keyboard and the extended keyboard, which has 15 additional special-function keys.

⇒	See also ADB; alphanumeric; Alt key; arrow keys; Backspace key; Break key; Caps Lock key; Control key; cursor; Delete key; Dvorak keyboard; End key; enhanced keyboard; Enter key; Escape key; function keys; Home key; Ins key; Num Lock key; Pause key; Page Down key; Page Up key; Print Screen key; QWERTY keyboard.


laser printer

A type of printer that utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. This is also the way copy machines work.

Because an entire page is transmitted to a drum before the toner is applied, laser printers are sometimes called page printers. There are two other types of page printers that fall under the category of laser printers even though they do not use lasers at all. One uses an array of LEDs to expose the drum, and the other uses LCDs. Once the drum is charged, however, they both operate like a real laser printer.

One of the chief characteristics of laser printers is their resolution—how many dots per inch (dpi) they lay down. The available resolutions range from 300 dpi at the low end to 1,200 dpi at the high end. By comparison, offset printing usually prints at 1,200 or 2,400 dpi. Some laser printers achieve higher resolutions with special techniques known generally as resolution enhancement.

In addition to the standard monochrome laser printer, which uses a single toner, there also exist color laser printers that use four toners to print in full color. Color laser printers tend to be about five to ten times as expensive as their monochrome siblings.

Laser printers produce very high-quality print and are capable of printing an almost unlimited variety of fonts. Most laser printers come with a basic set of fonts, called internal or resident fonts, but you can add additional fonts in one of two ways:

font cartridges: Laser printers have slots in which you can insert font cartridges, ROM boards on which fonts have been recorded. The advantage of font cartridges is that they use none of the printer's memory.

soft fonts: All laser printers come with a certain amount of RAM memory, and you can usually increase the amount of memory by adding memory boards in the printer's expansion slots. You can then copy fonts from a disk to the printer's RAM. This is called downloading fonts. A font that has been downloaded is often referred to as a soft font, to distinguish it from the hard fonts available on font cartridges. The more RAM a printer has, the more fonts that can be downloaded at one time.

In addition to text, laser printers are very adept at printing graphics. However, you need significant amounts of memory in the printer to print high-resolution graphics. To print a full-page graphic at 300 dpi, for example, you need at least 1 MB (megabyte) of printer RAM. For a 600-dpi graphic, you need at least 4 MB RAM.

Because laser printers are nonimpact printers, they are much quieter than dot-matrix or daisy-wheel printers. They are also relatively fast, although not as fast as some dot-matrix printers. The speed of laser printers ranges from about 4 to 20 pages of text per minute (ppm). A typical rate of 6 ppm is equivalent to about 40 characters per second (cps).

Laser printers are controlled through page description languages (PDLs). There are two de facto standards for PDLs:

PCL: Hewlett-Packard (HP) was one of the pioneers of laser printers and has developed a Printer Control Language (PCL) to control output. There are several versions of PCL, so a printer may be compatible with one but not another. In addition, many printers that claim compatibility cannot accept HP font cartridges.

PostScript: This is the de facto standard for Apple Macintosh printers and for all desktop publishing systems.

Most software can print using either of these PDLs. PostScript tends to be a bit more expensive, but it has some features that PCL lacks and it is the standard for desktop publishing. Some printers support both PCL and PostScript.

⇒	See also color printer; font cartridge; LCD printer; offset printing; Page Description Language; PCL; PostScript; printer; resident font; resolution enhancement; smoothing; soft font; toner.


modem

Acronym for modulator-demodulator. A modem is a device that enables a computer to transmit data over telephone lines ( [image]). Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms. (Note that ISDN telephone lines send data digitally, so they do not require modems.)

Fortunately, there is one standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have. There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems and are more machine specific.

While the modem interfaces are standardized, a number of different protocols for formatting data to be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, while others have been developed by private companies. Most modems have built-in support for the more common protocols—at slow data transmission speeds at least, most modems can communicate with each other. At high transmission speeds, however, the protocols are less standardized.

Aside from the transmission protocols that they support, the following characteristics distinguish one modem from another:

bps: How fast the modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 28,800 bps, although they can achieve even higher data transfer rates by compressing the data. Obviously, the faster the transmission rate, the faster you can send and receive data. Note, however, that you cannot receive data any faster than it is being sent. If, for example, the device sending data to your computer is sending it at 2,400 bps, you must receive it at 2,400 bps. It does not always pay, therefore, to have a very fast modem. In addition, some telephone lines are unable to transmit data reliably at very high rates.

voice/data: Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication.

auto-answer: An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use.

data compression: Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique.

flash memory: Some modems come with flash memory rather than conventional ROM, which means that the communications protocols can be easily updated if necessary.

To get the most out of a modem, you should have a communications software package, a program that simplifies the task of transferring data.

⇒	See also bps; CCITT; communications; communications protocol; communications software; data compression; flash memory; Hayes compatible; MNP; RS-232C.


monitor

(1) Another term for display screen. The term monitor, however, usually refers to the entire box, whereas display screen can mean just the screen. In addition, the term monitor often implies graphics capabilities.

There are many ways to classify monitors. The most basic is in terms of color capabilities, which separates monitors into three classes:

monochrome: Monochrome monitors actually display two colors, one for the background and one for the foreground. The colors can be black and white, green and black, or amber and black.

gray-scale: A gray-scale monitor is a special type of monochrome monitor capable of displaying different shades of gray.

color: Color monitors can display anywhere from 16 to over 1 million different colors. Color monitors are sometimes called RGB monitors because they accept three separate signals—red, green, and blue.

Color and gray-scaling monitors are often classified by the number of bits they use to represent each pixel. For example, an 8-bit monitor represents each pixel with 8 bits. The more bits per pixel, the more colors and shades of gray the monitor can display.

After this classification, the most important aspect of a monitor is its screen size. Like televisions, screen sizes are measured in diagonal inches, the distance from one corner to the opposite corner diagonally. A typical size for VGA monitors is 14 inches. Monitors that are 16 or more inches diagonally are often called full-page monitors. In addition to their size, monitors can be either portrait (height greater than width) or landscape (width greater than height). Larger landscape monitors can display two full pages, side by side.

The resolution of a monitor indicates how densely packed the pixels are. In general, the more pixels (often expressed in dots per inch), the sharper the image. Most modern monitors can display 1024 by 768 pixels, the SVGA standard. Some high-end models can display 1280 by 1024, or even 1800 by 1200.

Another common way of classifying monitors is in terms of the type of signal they accept: analog or digital. Low-cost digital monitors are often called TTL monitors. Most monitors accept analog signals, which is required by the VGA, SVGA, 8514/A, and other high-resolution color standards. Some monitors are capable of accepting either type of signal.

Some monitors are fixed frequency, which means that they accept input at only one frequency. Another type of monitor, called a multiscanning monitor, automatically adjusts to the frequency of the signals being sent to it. This means that it can accept input from different types of video adapters. Like fixed-frequency monitors, multiscanning monitors accept TTL, analog, or both types of input.

Other factors that determine a monitor's quality include the following:

bandwidth: The range of signal frequencies the monitor can handle. This determines how much data it can process.

refresh rate: How many times per second the screen is refreshed (redrawn). To avoid flickering, the refresh rate should be at least 70 Hz.

interlaced or noninterlaced: Interlacing is a technique that enables a monitor to have more resolution, but it reduces the monitor's reaction speed.

dot pitch: The amount of space between each pixel. The smaller the dot pitch, the sharper the image. However, very small dot pitches may also translate into decreased brightness and contrast.

convergence: The clarity and sharpness of each pixel.

⇒	See also analog monitor; bandwidth; convergence; digital monitor; display screen; dot pitch; dpi; fixed-frequency monitor; gray scaling; interlacing; monochrome; multiscanning monitor; pixel; refresh; RGB monitor; SVGA; TTL monitor; VGA; video adapter.

(1) 	A program that observes a computer. For example, some monitor programs report how often another program accesses a disk drive or how much CPU time it uses.


operating system

The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers ( [image]).

For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop—it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

Operating systems can be classified as follows:

multi-user: Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.

multiprocessing: Supports running a program on more than one CPU.

multitasking: Allows more than one program to run concurrently.

multithreading: Allows different parts of a single program to run concurrently.

real-time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.

Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Xenix.

As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.

⇒	See also BIOS; command processor; file management; DOS; multiprocessing; multitasking; multithreading; multi-user; OS/2; UNIX; Microsoft Windows.


optical scanner

A device that can read text or illustrations printed on paper and translate the information into a form the computer can use. A scanner works by digitizing an image—dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. (For color and gray scaling, the same principle applies, but each box is then represented by up to 24 bits.) The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen, and manipulated by programs ( [image]).

Optical scanners do not distinguish text from illustrations; they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR) system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages.

Scanners differ from one another in the following respects:

scanning technology: Most scanners use charge-coupled device (CCD) arrays, which consist of tightly packed rows of light receptors that can detect variations in light intensity and frequency. The quality of the CCD array is probably the single most important factor affecting the quality of the scanner. Industry-strength drum scanners use a different technology that relies on a photomultiplier tube (PMT), but this type of scanner is much more expensive than the more common CCD-based scanners.

resolution: The denser the bit map, the higher the resolution. Typically, scanners support resolutions of from 72 to 600 dpi.

bit depth: The number of bits used to represent each pixel. The greater the bit depth, the more colors or grayscales can be represented. For example, a 24-bit color scanner can represent 224 (16.7 million) colors. Note, however, that a large color range is useless if the CCD arrays are capable of detecting only a small number of distinct colors.

size and shape: Some scanners are small hand-held devices that you move across the paper ( [image]). These hand-held scanners are often called half-page scanners because they can only scan 2 to 5 inches at a time. Hand-held scanners are adequate for small pictures and photos, but they are difficult to use if you need to scan an entire page of text or graphics.

Larger scanners include machines into which you can feed sheets of paper. These are called sheet-fed scanners. Sheet-fed scanners are excellent for loose sheets of paper, but they are unable to handle bound documents.

A second type of large scanner, called a flatbed scanner, is like a photocopy machine. It consists of a board on which you lay books, magazines, and other documents that you want to scan.

Overhead scanners (also called copyboard scanners) look somewhat like overhead projectors. You place documents faceup on a scanning bed, and a small overhead tower moves across the page.

⇒	See also ASCII; bit map; CCD; fax machine; font; gray scaling; optical character recognition; resolution; TWAIN.


programming language

A vocabulary and set of grammatical rules for instructing a computer to perform specific tasks. The term programming language usually refers to high-level languages, such as BASIC, C, C++, COBOL, FORTRAN, and Pascal. Each language has a unique set of keywords (words that it understands) and a special syntax for organizing program instructions.

High-level programming languages, while simple compared to human languages, are more complex than the languages the computer actually understands, called machine languages. Each different type of CPU has its own unique machine language.

Lying between machine languages and high-level languages are languages called assembly languages ( [image]). Assembly languages are similar to machine languages, but they are much easier to program in because they allow a programmer to substitute names for numbers. Machine languages consist of numbers only.

Lying above high-level languages are languages called fourth-generation languages (usually abbreviated 4GL). 4GLs are far removed from machine languages and represent the class of computer languages closest to human languages.

Regardless of what language you use, eventually you need to convert your program into machine language so that the computer can understand it. There are two ways to do this:

•	compile the program

•	interpret the program

See compile and interpreter for more information about these two methods.

The question of which language is best is one that consumes a lot of time and energy among computer professionals. Every language has its strengths and weaknesses. For example, FORTRAN is a particularly good language for processing numerical data, but it does not lend itself very well to organizing large programs. Pascal is very good for writing well-structured and readable programs, but it is not as flexible as the C programming language. C++ embodies powerful object-oriented features, but it is complex and difficult to learn.

The choice of which language to use depends on the type of computer the program is to run on, what sort of program it is, and the expertise of the programmer.

⇒	See also assembly language; BASIC; C; C++; compiler; fourth-generation language; high-level language; FORTRAN; interpreter; language; machine language; LISP; object-oriented programming; Pascal; syntax.


spreadsheet

A table of values arranged in rows and columns. Each value can have a predefined relationship to the other values. If you change one value, therefore, you may need to change other values as well.

Spreadsheet applications (often referred to simply as spreadsheets) are computer programs that let you create and manipulate spreadsheets electronically. In a spreadsheet application, each value sits in a cell. You can define what type of data is in each cell and how different cells depend on one another. The relationships between cells are called formulas, and the names of the cells are called labels.

Once you have defined the cells and the formulas for linking them together, you can enter your data. You can then modify selected values to see how all the other values change accordingly. This enables you to study various what-if scenarios.

A simple example of a useful spreadsheet application is one that calculates mortgage payments for a house. You would define five cells:

1. total cost of the house

2. down payment

3. mortgage rate

4. mortgage term

5. monthly payment

Once you had defined how these cells depend on one another, you could enter numbers and play with various possibilities. For example, keeping all the other values the same, you could see how different mortgage rates would affect your monthly payments.

There are a number of spreadsheet applications on the market, Lotus 1-2-3 and Excel being among the most famous. The more powerful spreadsheet applications support graphics features that enable you to produce charts and graphs from the data.

Some spreadsheets are multidimensional, meaning that you can link one spreadsheet to another. A three-dimensional spreadsheet, for example, is like a stack of spreadsheets all connected by formulas. A change made in one spreadsheet automatically affects other spreadsheets.

⇒	See also cell; Excel; formula; label; Lotus 1-2-3; three-dimensional spreadsheet.


standard

A definition or format that has been approved by a recognized standards organization or is accepted as a de facto standard by the industry. Standards exist for programming languages, operating systems, data formats, communications protocols, and electrical interfaces.

From a user's standpoint, standards are extremely important in the computer industry because they allow the combination of products from different manufacturers to create a customized system. Without standards, only hardware and software from the same company could be used together. In addition, standard user interfaces can make it much easier to learn how to use new applications.

Most official computer standards are set by one of the following organizations:

•	ANSI (American National Standards Institute)

•	CCITT (Comité Consultatif Internationale Télégraphique et Téléphonique)

•	IEEE (Institute of Electrical and Electronic Engineers)

•	ISO (International Standards Organization)

•	VESA (Video Electronics Standards Association)

IEEE sets standards for most types of electrical interfaces. Its most famous standard is probably RS-232C, which defines an interface for serial communication. This is the interface used by most modems, and a number of other devices, including display screens and mice. IEEE is also responsible for designing floating-point data formats.

While IEEE is generally concerned with hardware, ANSI is primarily concerned with software. ANSI has defined standards for a number of programming languages, including C, COBOL, and FORTRAN.

CCITT defines international standards, particularly communications protocols. It has defined a number of standards, including V.22, V.32, V.34 and V.42, that specify protocols for transmitting data over telephone lines.

In addition to standards approved by organizations, there are also de facto standards. These are formats that have become standard simply because a large number of companies have agreed to use them. They have not been formally approved as standards, but they are standards nonetheless. PostScript is a good example of a de facto standard.

⇒	See also ANSI; architecture; CCITT; compatible; de facto standard; IEEE; ISO; open architecture; VESA.


word processing

Using a computer to create, edit, and print documents. Of all computer applications, word processing is the most common. To perform word processing, you need a computer, a special program called a word processor, and a printer. A word processor enables you to create a document, store it electronically on a disk, display it on a screen, modify it by entering commands and characters from the keyboard, and print it on a printer.

The great advantage of word processing over using a typewriter is that you can make changes without retyping the entire document. If you make a typing mistake, you simply back up the cursor and correct your mistake. If you want to delete a paragraph, you simply remove it, without leaving a trace. It is equally easy to insert a word, sentence, or paragraph in the middle of a document. Word processors also make it easy to move sections of text from one place to another within a document, or between documents. When you have made all the changes you want, you can send the file to a printer to get a hardcopy.

Word processors vary considerably, but all word processors support the following basic features:

insert text: Allows you to insert text anywhere in the document.

delete text: Allows you to erase characters, words, lines, or pages as easily as you can cross them out on paper.

cut and paste: Allows you to remove (cut) a section of text from one place in a document and insert (paste) it somewhere else.

copy: Allows you to duplicate a section of text.

page size and margins: Allows you to define various page sizes and margins, and the word processor will automatically readjust the text so that it fits.

search and replace: Allows you to direct the word processor to search for a particular word or phrase. You can also direct the word processor to replace one group of characters with another everywhere that the first group appears.

word wrap: The word processor automatically moves to the next line when you have filled one line with text, and it will readjust text if you change the margins.

print: Allows you to send a document to a printer to get hardcopy.

Word processors that support only these features (and maybe a few others) are called text editors. Most word processors, however, support additional features that enable you to manipulate and format documents in more sophisticated ways. These more advanced word processors are sometimes called full-featured word processors. Full-featured word processors usually support the following features:

file management: Many word processors contain file management capabilities that allow you to create, delete, move, and search for files.

font specifications: Allows you to change fonts within a document. For example, you can specify bold, italics, and underlining. Most word processors also let you change the font size and even the typeface.

footnotes and cross-references: Automates the numbering and placement of footnotes and enables you to easily cross-reference other sections of the document.

graphics: Allows you to embed illustrations and graphs into a document. Some word processors let you create the illustrations within the word processor; others let you insert an illustration produced by a different program.

headers, footers, and page numbering: Allows you to specify customized headers and footers that the word processor will put at the top and bottom of every page. The word processor automatically keeps track of page numbers so that the correct number appears on each page.

layout: Allows you to specify different margins within a single document and to specify various methods for indenting paragraphs.

macros: A macro is a character or word that represents a series of keystrokes. The keystrokes can represent text or commands. The ability to define macros allows you to save yourself a lot of time by replacing common combinations of keystrokes.

merges: Allows you to merge text from one file into another file. This is particularly useful for generating many files that have the same format but different data. Generating mailing labels is the classic example of using merges.

spell checker: A utility that allows you to check the spelling of words. It will highlight any words that it does not recognize.

tables of contents and indexes: Allows you to automatically create a table of contents and index based on special codes that you insert in the document.

thesaurus: A built-in thesaurus that allows you to search for synonyms without leaving the word processor.

windows: Allows you to edit two or more documents at the same time. Each document appears in a separate window. This is particularly valuable when working on a large project that consists of several different files.

WYSIWYG (what you see is what you get):  With WYSIWYG, a document appears on the display screen exactly as it will look when printed.

The line dividing word processors from desktop publishing systems is constantly shifting. In general, though, desktop publishing applications support finer control over layout, and more support for full-color documents.

⇒	See also copy; cut; delete; desktop publishing; editor; font; footer; graphics; header; hyphenation; insert; justify; layout; macro; margins; merge; paste; spell checker; word wrap; WYSIWYG.


Table:Typical Access Times for Different Computer Devices

Device	Typical Access Times
static RAM (SRAM)	10−50 nanoseconds
dynamic RAM (DRAM)	50−150 nanoseconds
EPROM	55−250 nanoseconds
read-only memory (ROM)	55−250 nanoseconds
Hard Disk Drive	9−30 milliseconds
Erasable Optical	19−200 milliseconds
CD-ROM	100−800 milliseconds
DAT tape drive	about 20 seconds
QIC tape drive	about 40 seconds
8 mm tape drive	40−500 seconds


Table: Alphanumeric, Punctuation, and Special Characters

Alphanumeric Characters	Special Characters	Punctuation Characters
a - z	Esc	; semicolon
A - Z	Tab	: colon
0 - 9		, comma
		" double quote
		' single quote
		# number sign or pound sign
		/ slash
		\ backslash
		* asterisk or star
		^ caret
		. period, point, or dot
		@ at sign
		& ampersand
		~ tilde
		! bang or exclamation mark
		- dash
		= equal sign
		— em dash
		– en dash
		… ellipsis


Table: ANSI Characters


Table: ASCII Control Characters

OCT	DEC	HEX	CHAR	SYMBOL	MEANING
0	0	0	^@	NUL	Null
1	1	1	^A	SOH	Start of Heading
2	2	2	^B	STX	Start of Text
3	3	3	^C	ETX	End of Text
4	4	4	^D	EQT	End of Transmit
5	5	5	^E	ENQ	Enquiry
6	6	6	^F	ACK	Acknowledge
7	7	7	^G	BEL	Bell
10	8	8	^H	BS	Backspace
11	9	9	^I	HT	Horizontal Tab
12	10	A	^J	LF	Line Feed
13	11	B	^K	VT	Vertical Tab
14	12	C	^L	FF	Form Feed
15	13	D	^M	CR	Carriage Return
16	14	E	^N	SO	Shift Out
17	15	F	^O	SI	Shift In
20	16	10	^P	DLE	Data Link Escape
21	17	11	^Q	DC1	Device Control 1
22	18	12	^R	DC2	Device Control 2
23	19	13	^S	DC3	Device Control 3
24	20	14	^T	DC4	Device Control 4
25	21	15	^U	NAK	Negative Acknowledge
26	22	16	^V	SYN	Synchronous Idle
27	23	17	^W	ETB	End Transmit Block
30	24	18	^X	CAN	Cancel
31	25	19	^Y	EM	End of Medium
32	26	1A	^Z	SUB	Substitution
33	27	1B	^[	ESC	Escape
34	28	1C	^|	FS	Figures Shift
35	29	1D	^]	GS	Group Separator
36	30	1E	^^	RS	Record Separator
37	31	1F	^	US	Unit Separator


Table: Standard ASCII (Alphanumeric Characters)

33	!	49	1	65	A	81	Q	97	a	113	q
34	“	50	2	66	B	82	R	98	b	114	r
35	#	51	3	67	C	83	S	99	c	115	s
36	$	52	4	68	D	84	T	100	d	116	t
37	%	53	5	69	E	85	U	101	e	117	u
38	&	54	6	70	F	86	V	102	f	118	v
39	'	55	7	71	G	87	W	103	g	119	w
40	(	56	8	72	H	88	X	104	h	120	x
41	)	57	9	73	I	89	Y	105	i	121	y
42	*	58	:	74	J	90	Z	106	j	122	z
43	+	59	;	75	K	91	[	107	k	123	{
44	,	60	<	76	L	92	\	108	l	124	|
45	-	61	=	77	M	93	]	109	m	125	}
46	.	62	>	78	N	94	^	110	n	126	~
47	/	63	?	79	O	95	_	111	o	127	_
48	0	64	@	80	P	96	`	112	p


Table: Extended ASCII (De Facto Standard for PCs)


Table: decimal and binary equivalents

Decimal	Binary
1	1
2	10
3	11
4	100
5	101
6	110
7	111
8	1000
9	1001
10	1010
16	10000
32	100000
64	1000000
100	1100100
256	10000000
512	100000000
1000	111111010
1024	1000000000


Table: Boolean Operators

x AND y	Result is TRUE if both x and y are TRUE. Otherwise the result is FALSE.
x OR y	Result is TRUE if either x or y is TRUE. Otherwise the result is FALSE.
x XOR y	Result is TRUE only if x and y have different values. Otherwise the result is FALSE.
NOT x	Result is TRUE if x is FALSE. Result is FALSE if x is TRUE.


Table: CD-ROM Drives

General Speed	Seek Time (milliseconds)	Data Transfer Rate
Single-Speed	600	150K per second
2X	320	300K per second
3X	250	450K per second
4X	125-220	600K per second
6X	135-145	900K per second


Table: Communications Protocols

Protocol	Maximum Transmission Rate	Duplex Mode
Bell 103	300 bps	Full
CCITT V.21	300 bps	Full
Bell 212A	1,200 bps	Full
CCITT V.22	1,200 bps	Half
CCITT V.22bis	2,400 bps	Full
CCITT V.29	9,600 bps	Half
CCITT V.32	9,600 bps	Full
CCITT V.32bis	14,400 bps	Full
CCITT V.34	28,800 bps	Full


Table: Floppy Disk Densities

		5¼-inches
	Single	Double	High
PC	360K	720K	1.2MB
Mac	NA	NA	NA
		3½-inch
	Single	Double	High
PC	NA	720K	1.44MB
Mac	400K	800K	1.2MB


Table: EBCDIC Codes

Decimal	Hexadecimal	Character	Decimal	Hexadecimal	Character
129	81	a	194	C2	B
130	82	b	195	C3	C
131	83	c	196	C4	D
132	84	d	197	C5	E
133	85	e	198	C6	F
134	86	f	199	C7	G
135	87	g	200	C8	H
136	88	h	201	C9	I
137	89	i	209	D1	J
145	91	j	210	D2	K
146	92	k	211	D3	L
147	93	l	212	D4	M
148	94	m	213	D5	N
149	95	n	214	D6	O
150	96	o	215	D7	P
151	97	p	216	D8	Q
152	98	q	217	D9	R
153	99	r	226	E2	S
162	A2	s	227	E3	T
163	A3	t	228	E4	U
164	A4	u	229	E5	V
165	A5	v	230	E6	W
166	A6	w	231	E7	X
167	A7	x	232	E8	Y
168	A8	y	233	E9	Z
169	A9	z	64	40	blank
240	F0	0	76	4C	<
241	F1	1	77	4D	(
242	F2	2	78	4E	+
243	F3	3	79	4F	|
244	F4	4	80	50	&
245	F5	5	90	5A	!
246	F6	6	91	5B	$
247	F7	7	92	5C	*
248	F8	8	93	5D	)
249	F9	9	94	5E	;
122	7A	:	96	60	-
123	7B	#	97	61	/
124	7C	@	107	6B	,
125	7D	'	108	6C	%
126	7E	=	109	6D	_
127	7F	“	110	6E	>
193	C1	A	111	6F	?


Table: Emoticons

Emoticon	Meaning
:-)	Joking
: 0	Bored
;-)	Winking
:-(	Sad
:-<	Frowning


Table: File Types

Batch file	Same as command file—contains operating system commands
Binary file	Contains data or instructions in binary format
Command file	Contains operating system commands
Data file	Contains data
Directory file	Contains bookkeeping information about files that are below it
Executable file	Contains a program or commands in an executable format
Library file	Contains functions in object format
Map file	Contains a map of a program
Object file	Contains code that has been compiled
Text file	Contains textual data (that is, data that can be read by humans), including files you create with a text editor and any file in ASCII format.


Table: Bit-Mapped Graphics File Formats

Format	Description
BMP	The bit-mapped file format used by Microsoft Windows.
GIF	The bit-mapped file format used by CompuServe and many other BBSs.
PCX	Originally developed by ZSOFT for its PC Paintbrush program, PCX is a common graphics file format supported by many graphics programs, as well as most optical scanners and fax modems.
TIFF (Tagged Image File Format)	A standard file format for storing images as bit maps. It is used especially for scanned images because it can support any size, resolution, and color depth.


Table: Vector Graphics File Formats

Format	Description
CGM (Computer Graphics Metafile)	A format developed by several standards organizations, CGM is supported by many PC software products.
DXF (Data Exchange File)	A format created by AutoDesk. Almost all PC-based CAD systems support DXF.
EPS (Encapsulated PostScript)	The file format for the PostScript language. EPS uses a combination of PostScript commands and TIFF or PICT formats.
GEM	The graphics file format used by GEM-based applications. GEM is a graphical user interface (GUI) developed by Digital Research.
HPGL (Hewlett-Packard Graphics Language)	One of the oldest file formats. Although it is not very sophisticated, it is supported by many PC-based graphics products.
IGES (Initial Graphics Exchange Specification)	An ANSI standard for three-dimensional wire frame models. IGES is supported by most PC-based CAD systems.
PIC (Lotus Picture File)	A relatively simple file format developed by Lotus for representing graphs generated by Lotus 1-2-3. PIC is supported by a wide variety of PC applications.
PICT	Developed by Apple Computer in 1984 as the standard format for storing and exchanging graphics files. It is supported by all graphics programs that run on a Macintosh.
WMF (Windows Metafile Format)	A file format for exchanging graphics between Microsoft Windows applications. WMF files can also hold bit-mapped images.


Table: Table of Hexadecimal Values

Decimal	Hexadecimal	Binary
0	0	0000
1	1	0001
2	2	0010
3	3	0011
4	4	0100
5	5	0101
6	6	0110
7	7	0111
8	8	1000
9	9	1001
10	A	1010
11	B	1011
12	C	1100
13	D	1101
14	E	1110
15	F	1111


Table: Intel Microprocessors

Micro-processor	Date	Estimated power (in MIPS)	Register Width (bits)	Bus Width (bits)	Clock Rates  (in MHz)	Notes
8086	1978	0.5	16	16	5, 8, and 10
8088	1979	0.5	16	8	5 and 8	Used in the original IBM PC and PC/XT.
80286	1982	1.5	16	16	8, 10, and 12	Supports virtual memory and an address space of 16MB (megabytes); is 5 to 20 times faster than the 8086
80386DX	1985	10	32	32	16, 20, 25, and 33	Built-in multitasking and virtual memory, has an address space of 4GB; is 2 to 4 times faster than the 80286
80386SX	1988	2.5	32	16	16, 20, 25, and 33	Compatible with both the 80286 and the 80386
80386SL	1990	5	32	32	20 and 25	Same architecture as the 80386DX, but with added power management features; popular in portable computers that rely on a battery for power.
80486DX	1989	30	32	32	25, 33 and 50	Similar to the 386 but much faster; uses a built-in memory cache to avoid wait states and includes a numeric coprocessor; uses pipelining techniques.
80486SX	1991	20	32	32	16, 20, 25, and 33	An inexpensive variety of the 80486DX that runs at low speeds and lacks a numeric coprocessor.
80486SL	1992	20	32	32	20, 25, and 33	Based on 80486DX architecture, with power management features for battery-operated computers.
80486DX2 and OverDrive	1992	50	32	32	50 and 66	Same architecture as the 80486DX, but with the internal clock speed doubled.
486DX4	1994	70	32	32	75 and 100	Same architecture as the 80486DX, but with the internal clock rate tripled.
Pentium	1993	125	32	64	60, 66, 75, 100,  120, 133, and 180	Although basically a CISC architecture, the Pentium chip includes many RISC features, such as pipelining and superscaling; contains more than 3 million transistors.
Pentium OverDrive	1995		32	64	60, 66, and 100	A Pentium chip that can be installed in a 486-based computer that has an OverDrive socket.


Table: Special Keys on PC Keyboards

Alt key	Short for Alternate, this key is like a second Control key.
Arrow keys	Most keyboards have four arrow keys that enable you to move the cursor (or insertion point) up, down, right, or left. Used in conjunction with the Shift or Alt keys, the arrow keys can move the cursor more than one position at a time, but this depends on which program is running.
Backspace key	Deletes the character just to the left of the cursor (or insertion point) and moves the cursor to that position.
Caps Lock Key	A toggle key that, when activated, causes all alphabetic characters to be uppercase.
Ctrl key	Short for Control, this key is used in conjunction with other keys to produce control characters. The meaning of each control character depends on which program is running.
Delete key	Sometimes labeled Del, deletes the character at the current cursor position, or the selected object, but does not move the cursor. For graphics-based applications, the Delete key deletes the character to the right of the insertion point.
Enter key	Used to enter commands or to move the cursor to the beginning of the next line. Sometimes labeled Return instead of Enter.
Esc key	Short for Escape, this key is used to send special codes to devices and to exit (or escape) from programs and tasks.
Fn key	Short for Function, this key is used in conjunction with other keys to produce special actions that vary depending on which program is running. This key is found most frequently on portable computers that do not have full-size keyboards.
Function Keys	Special keys labeled F1 to Fx, x being the number of function keys on the keyboard. These keys have different meanings depending on which program is running.
Return key	Another name for the Enter key.


Table: Octal and Binary Equivalents

Octal	Binary
0	000
1	001
2	010
3	011
4	100
5	101
6	110
7	111


Table: Paint Tools

Icon	Tool	Function
	Brush	For freehand painting using the currently selected pattern and color. Most paint programs provide differently shaped brushes for different styles of painting.
	Eraser	For erasing selected areas of the display screen.
	Lasso	For selecting parts of an illustration.
	Pen	For drawing freehand lines.
	Scissors	For cutting a section of a painting.
	Spraycan	For spray painting in the current pattern and color.


Table: QIC Standards

QIC Type	Capacity	Cartridge Size
QIC-24	60MB	Full
QIC-40	40MB	Mini
QIC-80	80MB 120MB	Mini
QIC-100	20MB 40MB	Mini
QIC-120	125MB	Full
QIC-128	86MB 128MB	Mini
QIC-150	150MB 250MB	Full
QIC-380	380MB	Mini
QIC-525	320MB 525MB	Full
QIC-1000	1.01GB	Full
QIC-1350	1.35GB	Full
QIC-2000	2GB	Mini
QIC-3010	340MB	Mini
QIC-3020	680MB	Mini


Table: Relational Operators

Symbol	Mnemonic	Meaning
=	EQ	Equal to
<> (or !=)	NE	Not equal to
>	GT	Greater than
>=	GE	Greater than or equal to
<	LT	Less than
<=	LE	Less than or equal to


Table: Scientific Notation

Number in Normal Notation	In Scientific Notation
0.0004	4.0E-4
1,000,000,000.0	1.0E9
-37.456	-3.7456E2
-0.000000349	-3.49E-7


Table: Tapes

Type	Capacity	Notes
Half-inch	60MB to 400MB	Half-inch tapes come both as 9-track reels and as cartridges. The tapes themselves are relatively cheap but they require expensive tape drives.
Quarter-inch	40MB to 5GB	Quarter-inch cartridges (QIC tapes) are relatively inexpensive and support fast data transfer rates. Quarter-inch minicartridges are even less expensive, but their data capacities are smaller and their transfer rates are slower.
8-mm Helical-scan	1GB to 5GB	8-mm helical-scan cartridges use the same technology as VCR tapes and have the greatest capacity (along with DAT cartridges), but they require relatively expensive tape drives. They also have relatively slow data transfer rates.
4-mm DAT	1.3GB	DAT (Digital Audio Tape) cartridges have the greatest capacity (along with 8-mm helical-scan cartridges) but they require relatively expensive tape drives. They also have relatively slow data transfer rates.


Table: Popular Video Standards for PCs

Video Standard	Resolution	Simultaneous Colors
VGA (Video Graphics Array)	640 by 480	16
	320 by 200	256
SVGA	800 by 600	16
	1,024 by 768	256
	1,280 by 1,024	256
	1,600 by 1,200	256
8514/A	1,024 by 768	256
XGA (Extended Graphics Array)	640 by 480	65,536
	1,024 by 768	256
TI 34010	1,024 by 768	256


Typical Access Times for Different Computer Devices

Alphanumeric, Punctuation, and Special Characters

ANSI Characters

ASCII Control Characters

Standard ASCII (Alphanumeric Characters)

Extended ASCII (De Facto Standard for PCs)

Decimal and Binary Equivalents

Boolean Operators

CD-ROM Drives

Communications Protocols

Floppy Disk Densities

EBCDIC Codes

Emoticons

File Types

Bit-Mapped Graphics File Formats

Vector Graphics File Formats

Table of Hexadecimal Values

Intel Microprocessors

Special Keys on PC Keyboards

Octal and Binary Equivalents

Paint Tools

QIC Standards

Relational Operators

Scientific Notation

Tapes

Popular Video Standards for PCs


.INI File

extension


386SX

Intel microprocessors


3DO

expansion board

multimedia


8086

Intel microprocessors


8514/A

interlacing

monochrome

palette

resolution

SVGA

video adapter

XGA


A/UX

UNIX


abort

bomb

crash

hang

shell


absolute address

address

relative address


absolute cell reference

constant

relative cell reference

spreadsheet


accelerator board

bus

coprocessor

CPU

expansion board

floating-point number

FPU

graphics accelerator

Intel microprocessors

main memory

microprocessor

motherboard

PC

RAM

ZIF socket


access

access time

byte

mass storage

memory

random access

read

write


access code

access

log on

password


access time

access

clock speed

CPU

cycle time

data transfer rate

disk cache

interleaving

wait state


acoustic coupler

modem

network


active

cell

graphical user interface (GUI)

spreadsheet

window


active matrix display

flat-panel display

LCD

TFT


ActiveX

browser

Component Object Model

Java

OLE


Ada

high-level language

modular architecture

real time


adapter

controller

expansion board

video adapter


ADB

bus

constant

Macintosh computer

port


add-in

add-on

cartridge

expansion board

OLE


add-on

add-in

cartridge

expansion board

expansion slot

printed circuit board


address

absolute address

address bus

address space

base address

disk

machine address

main memory

memory

offset

relative address

sector

track

URL


address bus

address

bus

CPU

main memory


address space

address

main memory

memory

virtual memory


aggregate function

database management system (DBMS)

function

spreadsheet


AIX

UNIX


alert box

box

dialog box

graphical user interface (GUI)

window


algorithm

artificial intelligence

program

programming language


alias

device

file

name

variable


aliasing

antialiasing

jaggies

resolution


alignment

draw program

justification

margins


Alpha Processor

RISC

workstation


alphanumeric

character

special character


Alt key

ASCII

control character

keyboard

Option key


Alta Vista

World Wide Web


ALU

CPU


America Online

online service


Amiga

graphics

microprocessor

MIDI

personal computer


analog

digital


analog monitor

analog

CRT

digital

digital monitor

monitor

multiscanning monitor

video adapter


anchor

desktop publishing


AND operator

Boolean operator

operand

operator


animation

multimedia


annotation

workgroup computing


ANSI

FDDI

portable

standard


ANSI Character Set

ASCII


ANSI.SYS

ANSI

BIOS

CONFIG.SYS

device driver

escape sequence


answer-only modem

modem


antialiasing

jaggies

resolution

smoothing


antivirus program

virus


API

application

interface

operating environment

routine


app

application


append

concatenate

insert


Apple Computer

graphical user interface (GUI)

LocalTalk

Macintosh computer

plug-and-play

PowerPC

QuickTime

RISC


Apple key

Command key


applet

application

Java

OLE


AppleTalk

local-area network (LAN)

LocalTalk

Macintosh computer

topology


application

applet

database management system (DBMS)

end user

operating system

software

spreadsheet

systems software

utility

word processor


ARC

data compression

ZIP


Archie

filename

gopher

Internet


architecture

client/server architecture

modular architecture

open architecture

proprietary

standard


archival backup

archive

backup

incremental backup


archive

ARC

archival backup

attribute

backup


ARCnet

Ethernet

local-area network (LAN)

token-ring network


area chart

presentation graphics


argument

option

parameter

routine


arithmetic expression

expression


ARPANET

Internet

NSFnet


array

data structure

data type

matrix

subscript

vector


arrow keys

keyboard


artificial intelligence

computer science

expert system

fuzzy logic

LISP

natural language

neural network

robotics

voice recognition


ascender

baseline

descender

x-height


ASCII

ASCII file

character set

EBCDIC

extended ASCII

text file

Unicode


ASCII file

ASCII

binary file


aspect ratio

graphics


assembler

assembly language

machine language


assembly language

assembler

compile

low-level language

machine language

programming language


assign

operator

statement

variable


associate

extension

filename


asterisk

wild card


asynchronous

communications

start bit

stop bit


AT

Intel microprocessors

PC


AT bus

backward compatible

bus

EISA

expansion board

IBM PC

ISA bus

local bus

MCA

PCI

VL-Bus


AT command set

Hayes compatible

modem


AT keyboard

keyboard


ATM

Ethernet

FDDI


attribute

DOS

field

file

hidden file


audit trail

security


authoring tool

hypertext

multimedia

programming language

script


auto-answer

fax machine

fax modem

modem


auto-redial

modem


auto-repeat

keyboard


autoexec.bat

batch file

boot


automatic recalculation

recalculate

spreadsheet


autosave

crash

save

word processing


autosizing

monitor

resolution

SVGA

VGA

video adapter


autotracing

bit map

bit-mapped graphics

EPS

optical scanner

PCX

PostScript

TIFF

vector graphics


AUX

COM

port


backbone

bus

network

node


background

display screen

foreground

Microsoft Windows

monitor

multitasking

spooling


backlighting

background

flat-panel display

notebook computer

supertwist


backslash

pathname

root directory


backspace

ASCII

Backspace key

cursor

keyboard

pointer


Backspace key

arrow keys

backspace

Delete key

keyboard


backup

archival backup

archive

data compression

DMA


backward compatible

compatible

upward compatible


bad sector

disk

format

sector


BAK file

autosave

extension


bandwidth

bus

EISA

I/O

PCI


bar chart

presentation graphics


base address

address

offset

relative address


baseband transmission

broadband ISDN (B-ISDN)

broadband transmission

channel

communications

ISDN

local-area network (LAN)

network


baseline

ascender

descender

font

typeface

x-height


BASIC

GW-BASIC

high-level language

interpreter

programming language


BAT file

batch file

extension

filename


batch file

autoexec.bat

BAT file

batch processing

DOS


batch processing

batch file

interactive

transaction processing


battery pack

NiCad battery pack

NiMH battery pack


baud

bps

modem


bay

disk drive

expansion board

mass storage

slot


Bell 103

asynchronous

baud

CCITT

communications protocol

full duplex

protocol


Bell 212A

asynchronous

baud

CCITT

communications protocol

full duplex

protocol


bells and whistles

feature


Bernoulli disk drive

disk

hard disk drive

mass storage


Bézier curve

draw program

graphics

vector graphics


Big Blue

IBM PC


binary

binary format

decimal

hexadecimal

octal


binary compatible

binary file

compatible

cross-platform

export

heterogeneous network

import


binary file

ASCII

ASCII file

binary format

executable file

text file


Binary File Transfer (BFT)

CCITT

fax modem

standard


binary format

ASCII

binary

binary file

EBCDIC

executable file

text file


bind

address

compile

link


BinHex

e-mail

Uuencode


BIOS

boot

flash memory

I/O

NetBIOS

Phoenix BIOS

PnP

shadowing


bit

address space

register


bit block transfer

graphics

pixel

video adapter


bit map

bit-mapped graphics

digitize

graphics

optical scanner

pixel

resolution


bit-mapped graphics

bit map

graphics

vector graphics


BITNET

Internet

network

wide-area network (WAN)


block

communications

select

word processing

Xmodem


block graphics

character mode


BMP

bit map

extension

graphics file formats


boilerplate

template


boldface

font

word processing


bomb

abort

bug

crash

hang

Macintosh computer


Boolean expression

Boolean logic

Boolean operator

expression

relational operator


Boolean logic

binary

Boolean expression

Boolean operator


Boolean operator

Boolean expression

Boolean logic

operator

query


boot

BIOS

cold boot

load

operating system

warm boot


box

alert box

button

dialog box

graphical user interface (GUI)

icon

window

zoom


bps

baud

CCITT

communications

modem


branch

directory

tree structure


Break key

keyboard


broadband ISDN (B-ISDN)

bps

broadband transmission

fiber optics

ISDN


broadband transmission

baseband transmission

broadband ISDN (B-ISDN)

channel

communications

local-area network (LAN)

network


broadcast

e-mail

fax


browse

browser

data structure

database management system (DBMS)

field

object oriented

record

surf


browser

ActiveX

browse

HTML

Mosaic

World Wide Web


buffer

cache

command buffer

disk cache

save

spooling


bug

bomb

crash

glitch

hang


built-in function

function


bulletin board system (BBS)

communications software

e-mail

modem

network

online service


bundled software

hardware

software


bus

ADB

address bus

AT bus

channel

clock speed

controller

EISA

Ethernet

expansion bus

Industry Standard Architecture (ISA) bus

local bus

network

PCI

topology


bus mouse

bus

mouse

serial port


button

click

dialog box

graphical user interface (GUI)

mouse

radio buttons


byte

gigabyte

kilobyte

megabyte


C

assembly language

C++

high-level language

machine language

programming language

UNIX


C++

C

high-level language

Java

object oriented

programming language


cache

buffer

disk cache

RAM disk


CAD

CAD/CAM

CAE

CAM

digitizing tablet

graphics

light pen

monitor

mouse

plotter

workstation


CAD/CAM

CAD

CADD

CAM


CADD

CAD

CAD/CAM


CAE

CAD


calculator

desk accessory (DA)

Microsoft Windows

program


calendar

PIM

scheduler

utility


call

function

routine


CAM

CAD

CAD/CAM

robotics


camera-ready

desktop publishing

imagesetter

offset printing

service bureau


Caps Lock key

keyboard

toggle

uppercase


capture

learn mode

screen capture


card

HyperCard

hypertext


caret

Control key


carpal tunnel syndrome

ergonomics


carriage

paper feed

printer


carriage return

line feed

return


cartridge

font cartridge

laser printer

removable hard disk

slot

toner


cascading windows

overlaid windows

tiled windows

window


case sensitive

lowercase

uppercase


CBT

courseware


CCD

digital camera

optical scanner


CCITT

baud

bps

communications protocol

data compression

e-mail

fax machine

fax modem

full duplex

half duplex

ISDN

MNP

modem

protocol

standard


CD-I (Compact Disc-Interactive)

CD-ROM

DVI

optical disk


CD-R drive

CD-ROM

CD-ROM player


CD-ROM

CD-I (Compact Disc-Interactive)

CD-R drive

CD-ROM player

compact disc

disk

erasable optical disk

mass storage

multimedia

optical disk


CD-ROM player

access time

bay

CD-R drive

CD-ROM

IDE interface

MPC

multimedia kit

parallel port

PhotoCD

SCSI


cdev

control panel


cell

field

formula

spreadsheet


Centronics interface

ECP

EPP

interface

parallel interface

standard


CGA

backward compatible

EGA

graphics mode

IBM PC

MCGA

palette

resolution

SVGA

text mode

VGA

video adapter

XGA


CGI

Java

World Wide Web


CGM

ANSI

graphics file formats

vector graphics


channel

bus

communications


character

alphanumeric

ASCII

character based

extended ASCII

graphics based


character based

character mode

extended ASCII

graphical user interface (GUI)

graphics based

text mode


character mode

ASCII

block graphics

character based

pixel

video adapter


character set

ASCII

character

control character

Unicode


chassis

desktop model computer

expansion board

printed circuit board

slot

tower model


chat

e-mail

online service


check box

box

dialog box

graphical user interface (GUI)

option


checksum

communications

CRC

error detection


chip

controller

CPU

integrated circuit (IC)

microprocessor

PGA

printed circuit board

semiconductor

SIMM


choose

click

command

Command key

graphical user interface (GUI)

menu

option

select


Chooser

desk accessory (DA)


CIE color model

CMYK

color matching

RGB monitor


Cinepak

codec

Indeo


CISC

architecture

CPU

machine language

RISC


class

object-oriented programming (OOP)


clear

display screen

memory

variable


click

choose

double click

drag

graphical user interface (GUI)

mouse

shift clicking


client/server architecture

architecture

local-area network (LAN)

network

node

peer-to-peer architecture

process

server


clip

crop

graphics

window


clip art

desktop publishing


clipboard

copy

cut

paste


clock speed

bus

CPU

instruction

microprocessor

wait state


clone

compatible

IBM PC

PC


close

graphical user interface (GUI)

open

save

window


cluster

file allocation table (FAT)

fragmentation

sector


CMOS

semiconductor


CMYK

color matching

color separation

desktop publishing

Intel microprocessors

offset printing

RGB monitor

spot color

WYSIWYP


coaxial cable

information highway

network


COBOL

high-level language

programming language


code

ASCII

compile

executable file

machine language

object code

program

source code


codec

Cinepak

Indeo

MPEG

QuickTime

Video for Windows


cold boot

boot


collapse

branch

hierarchical

root directory


color depth

optical scanner

video adapter


color management system (CMS)

CIE color model

CMYK

color matching

Pantone Matching System (PMS)

process colors

RGB monitor

WYSIWYP


color matching

CIE color model

CMYK

color management system (CMS)

RGB monitor


color monitor

monitor

RGB monitor

video adapter


color printer

CMYK

color separation

ink-jet printer

laser printer

printer

process colors


color separation

CMYK

color management system (CMS)

color printer

desktop publishing

process colors


column

cell

character mode

database management system (DBMS)

desktop publishing

display screen

field

spreadsheet

word processing


column graph

presentation graphics


COM

AUX

communications

port

serial


COM file

command

DOS

EXE file

executable file

extension

file


comma-delimited

export

import


command

BAT file

COM file

command driven

command language

command line

DOS

EXE file

external command

function keys

instruction

internal command

keyword

menu

user interface


command buffer

buffer

command

undo


command driven

command

menu driven

user interface


Command key

Apple key

Control key

keyboard


command language

command

command processor

graphical user interface (GUI)

operating system

shell


command line

command

prompt


command processor

command language

operating system


COMMAND.COM

command processor

internal command


communications

baseband transmission

communications protocol

communications software

modem

network

port


communications protocol

asynchronous

Bell 103

Bell 212A

bps

CCITT

communications

full duplex

half duplex

protocol


communications software

auto-answer

batch file

bulletin board system (BBS)

communications

communications protocol

editor

emulation

Kermit

log on

macro

mainframe

modem

multitasking

queue

script


compact disc

CD-ROM

erasable optical disk

mass storage

optical disk

WORM (write-once, read many)


compatible

backward compatible

binary compatible

clone

compatible

dBASE

emulation

font cartridge

IBM PC

PC

plug compatible

standard

upward compatible


compile

assembly language

bind

compiler

high-level language

interpreter

link

object code

programming language

source code


compiler

assembly language

compile

interpreter

link

object code

programming language

source code


Component Object Model

ActiveX

component software

componentware

OLE

OpenDoc


component software

Component Object Model

object-oriented programming (OOP)

OLE

OpenDoc


componentware

Component Object Model


composite video

NTSC

RGB monitor


compound document

document

OLE

OpenDoc


CompuServe Information Service

online service


computer

CPU

hardware

mainframe

microprocessor

minicomputer

personal computer

software

supercomputer

workstation


computer literacy

power user


computer science

artificial intelligence

program


computer system

computer

operating system


concatenate

append

character string


concatenation

concatenate


conditional

expression

programming language


conference

bulletin board system (BBS)

forum

online service


CONFIG.SYS

boot

configuration

driver


configuration

CONFIG.SYS

configuration file

control panel

DIP switch

jumper

parameter


configuration file

.INI File

CONFIG.SYS

configuration


configure

configuration


connect time

online service


connectivity

export

import


connector

DIN connector

interface

port


console

display screen

keyboard

terminal


constant

absolute cell reference

character string

formula

variable


context sensitive

Help


contiguous

fragmentation


continuous tone

digital

gray scaling

halftone


continuous-form paper

paper feed

tractor feed


control character

ASCII

Break key

Control key

keyboard


Control key

Apple key

Command key

Control key combination


Control key combination

command

Control key


control panel

cdev


control program

graphical user interface (GUI)

Microsoft Windows

operating environment

operating system


controller

adapter

AT bus

bus

chip

CPU

driver

EISA

expansion board

peripheral device

printed circuit board

SCSI


conventional memory

expanded memory

extended memory

main memory


convergence

graphics

monitor

pixel

RGB monitor


convert

export

import


cooperative multitasking

Microsoft Windows

multitasking

UNIX


coprocessor

accelerator board

CPU

floating-point number


copy

buffer

clipboard

cut

file management system

paste


copy protection

shareware

software piracy


Courier font

fixed pitch

font

monospacing


courseware

CBT


CP/M

DOS

operating system


cps

printer


CPU

ALU

chip

CISC

clock speed

coprocessor

Intel microprocessors

microprocessor

PowerPC

RISC


CPU time

CPU

multitasking


crash

abort

bomb

bug

fatal error

hang

head crash


CRC

checksum

communications protocol

error detection

Zmodem


crop

clip


crop marks

camera-ready

desktop publishing

offset printing


cross-platform

binary compatible

local-area network (LAN)

platform


CRT

display screen

monitor

refresh


current

active

default

working directory


cursor

arrow keys

digitizing tablet

mouse

pointer


cursor control keys

arrow keys

cursor

keyboard


cursor position

cursor

display screen

text mode


customer support

bulletin board system (BBS)

download


cut

buffer

clipboard

copy

delete

paste


cyber

cyberspace

virtual reality


cyberspace

information highway

online service

virtual reality


cycle time

access time

DRAM

SRAM


cylinder

hard disk

platter

track


daisy chain

SCSI


daisy-wheel printer

impact printer

printer


DAT

gigabyte

helical-scan cartridge

mass storage

megabyte

sequential access

tape


data

ASCII

binary

data dictionary

database management system (DBMS)

program

software


data compression

ARC

CCITT

DSP

JPEG

lossless compression

lossy compression

MNP

MPEG

ZIP


data dictionary

database management system (DBMS)


data entry

database

spreadsheet


data processing

accounting software

application


data structure

array

file

record

tree structure


data transfer rate

access time


data type

character

database

declare

field

floating-point number

integer

variable


database

database management system (DBMS)

distributed database

field

file

hypertext

record

relational database


database management system (DBMS)

data dictionary

database

distributed database

flat-file database

fourth-generation language

hypertext

query

relational database

report writer

SQL


dBASE

database management system (DBMS)

export

import


DDE

interprocess communication (IPC)

OLE


de facto standard

Hayes compatible

Kermit

PCL

PostScript

standard

Xmodem


debug

bug


debugger

bug


decimal

binary

floating-point number

hexadecimal

integer

octal


declare

data type

programming language

variable


decrement

increment


decryption

encryption

security


dedicated

channel

expansion slot

network

server


delete

cut


Delete key

backspace

Backspace key

insertion point

keyboard


delimiter

pathname


demand paging

paging

RAM

swap

virtual memory


density

disk

disk drive

double-density disk

FDHD

floppy disk

high-density disk


descender

ascender

baseline

x-height


desk accessory (DA)

utility


desktop

graphical user interface (GUI)


desktop model computer

chassis

tower model


desktop publishing

color separation

offset printing

page layout program

service bureau


device

computer

CONFIG.SYS

driver

input device


device dependent

machine dependent


dial-up access

Internet

leased line

modem

POP


dialog box

box

graphical user interface (GUI)

pop-up window

window


digital

analog

digitize

modem


digital camera

digital

PhotoCD


digital cash

Internet


digital monitor

analog

analog monitor

digital

monitor

video adapter


digitize

bit map

digital

optical scanner

sampling


digitizing tablet

cursor

input device

mouse


DIN connector

connector


dingbat

font


DIP

chip


DIP switch

chip

configuration

expansion board

printed circuit board

toggle


direct-connect modem

acoustic coupler

modem


directory

file

file management system

folder

hierarchical

path

root directory

tree structure


disc

disk

optical disk


disk

CD-ROM

disk drive

erasable optical disk

floppy disk

format

hard disk

head

mass storage

optical disk

removable hard disk


disk cache

access time

buffer

cache

disk drive

RAM


disk controller

controller

disk drive

EISA

IDE interface

SCSI


disk drive

disk

floppy disk

hard disk

mass storage

optical disk


disk optimizer

fragmentation


disk pack

hard disk

removable hard disk


diskless workstation

disk drive

local-area network (LAN)

server

workstation


display screen

CAD/CAM

desktop publishing

flat-panel display

graphics

monitor

notebook computer

resolution


distributed database

database

database management system (DBMS)

distributed processing

network


distributed processing

database management system (DBMS)

distributed database

local-area network (LAN)

parallel processing


dithering

gray scaling

halftone


DMA

backup

channel

CPU

DIP switch

expansion board

jumper

main memory

real time


DNS

domain

domain name

IPC


docking station

bay

desktop model computer

expansion board

notebook computer

portable

slot


document

compound document

documentation

file


documentation

Help


domain

DNS

domain name

Internet


domain name

DNS

domain

InterNIC

IP address


DOS

Microsoft Windows

operating system

OS/2

PC


dot

bit map

dpi

extension

filename

resolution


dot pitch

monitor

pixel


dot-matrix printer

impact printer

printer


double click

click

mouse


double precision

floating-point number

IEEE


double-density disk

density

floppy disk


double-sided disk

disk drive

floppy disk


down

crash


download

bulletin board system (BBS)

font

online service

upload


dpi

dot

laser printer

resolution


draft mode

dot-matrix printer

letter quality (LQ)

near letter quality


draft quality

dot-matrix printer

draft mode

letter quality (LQ)

near letter quality


drag

drag-and-drop

graphical user interface (GUI)

mouse

select


drag-and-drop

drag

graphical user interface (GUI)


DRAM

dynamic RAM

EDO DRAM


draw program

graphics

paint program

vector graphics


drive bay

bay

disk drive

mass storage


driver

CONFIG.SYS

controller

device


drop cap

desktop publishing


DSP

coprocessor

data compression

digitize

graphics accelerator

sound card


dual-scan display

active matrix display

flat-panel display

LCD

passive-matrix display


dumb terminal

display screen

intelligent terminal

smart terminal

terminal


dummy

variable


DVI

CD-I (Compact Disc-Interactive)

codec

Indeo

MPEG


Dvorak keyboard

keyboard

macro

QWERTY keyboard


DXF

CAD

graphics

graphics file formats


dynamic

dynamic variable

static variable


dynamic acceleration

mouse

resolution


dynamic RAM

main memory

RAM

refresh

SRAM


dynamic variable

static variable

variable


e-mail

BinHex

CCITT

gateway

Internet Message Access Protocol

mailbox

MAPI

network

online service

POP

username

Uuencode

workgroup computing


EBCDIC

ASCII


ECP

Centronics interface

parallel port


edge connector

printed circuit board


editor

word processing


EDO DRAM

access time

cycle time

DRAM


EEMS

expanded memory

LIM memory


EEPROM

EPROM

flash memory

memory

PROM

RAM

ROM


EGA

CGA

video adapter


EIDE

ESDI

IDE interface

SCSI


EISA

bus

expansion board

ISA bus

local bus

Micro Channel Architecture (MCA)

multiprocessing

PCI

VL-Bus


electroluminescent display (ELD)

active matrix display

flat-panel display

gas-plasma display

LCD

notebook computer


electronic publishing

CD-ROM

multimedia

online service


embedded command

command

font

word processing


embedded object

document

OLE


emoticon

e-mail


EMS

expanded memory


emulation

communications software

compatible

log on

mainframe

terminal


encryption

decryption

password

security


End key

keyboard


end user

user


Energy Star

green PC


Enhanced Keyboard

function keys

keyboard


Enter key

Return key


environment

DOS

operating system

parameter

platform


EPP

Centronics interface

parallel port


EPROM

EEPROM

memory

PROM


EPS

graphics

graphics file formats

PostScript


erasable optical disk

access time

CD-ROM

disk

floppy disk

mass storage

optical disk


ergonomics

carpal tunnel syndrome


error detection

CCITT

checksum

CRC

Kermit

MNP

Xmodem


ESC

escape character

Escape key


escape character

escape sequence

keyboard


Escape key

abort

ESC

keyboard


escape sequence

escape character


ESDI

disk drive

EIDE

IDE interface

SCSI

ST-506 interface


Ethernet

ATM

IEEE

local-area network (LAN)

network

protocol

topology


even header

header


even parity

parity checking


exclusive OR

Boolean operator


EXE file

COM file

executable file

extension

program


executable file

assembler

binary file

binary format

COM file

compiler

EXE file

file

source code


execute

launch


expanded memory

conventional memory

EEMS

extended memory

main memory

RAM disk


expansion board

accelerator board

adapter

add-in

add-on

CPU

expansion slot

graphics accelerator

PCI

printed circuit board

sound card

video adapter


expansion bus

bus

EISA

expansion board

local bus

PCI

protocol

VL-Bus


expansion slot

expansion board

local bus

printed circuit board


expert system

artificial intelligence


exploded view

spreadsheet


export

comma-delimited

convert

filter

import


expression

arithmetic expression

Boolean expression

character string

data type

floating-point number

formula

integer

operand

operator

query


extended ASCII

ASCII

character based


extended memory

conventional memory

expanded memory

high memory area

protected mode

RAM disk

XMS


extension

associate

BAK file

BAT file

COM file

dot

init

memory resident


external command

command

COMMAND.COM

internal command


external modem

internal modem

modem


FAQ

Help

hypertext


fatal error

abort

crash


fax

fax machine


fax machine

bps

digitize

fax modem

optical scanner

thermal printer


fax modem

broadcast

fax machine

modem

optical scanner


FDDI

ATM

fiber optics

network

protocol


FDHD

density

DOS

floppy disk

Macintosh computer

SuperDrive


feathering

justification

vertical justification


feature

bells and whistles


fiber optics

FDDI

ISDN

local-area network (LAN)


field

attribute

cell

data type

database

database management system (DBMS)

record


file

directory

document

executable file

filename

folder

library


file allocation table (FAT)

cluster

disk

file

fragmentation


file format

file

format

graphics file formats


file management system

directory

hierarchical


filename

alias

directory

extension

file


fill

graphics

spreadsheet


filter

export

image editor

image enhancement

import

photo illustration


Finder

clipboard

desktop

file management system

MultiFinder

multitasking


firewall

intranet

network

security


firmware

hardware

PROM

ROM

software


fixed length

database management system (DBMS)

field

record

variable length


fixed pitch

Courier font

font

monospacing

pitch

proportional spacing


fixed width

fixed pitch

font


fixed-frequency monitor

monitor

multiscanning monitor


flame

conference

e-mail

forum

online service


flash memory

BIOS

EEPROM


flat technology monitor

CRT

flat-panel display

monitor


flat-file database

database management system (DBMS)

relational database


flat-panel display

active matrix display

backlighting

display screen

dual-scan display

electroluminescent display (ELD)

gas-plasma display

LCD

notebook computer

TFT


flatbed scanner

optical scanner


floating

palette


floating-point number

data type

double precision

FPU

precision

scientific notation


floppy disk

density

disk

FDHD

floppy drive


floppy drive

disk drive

floppy disk


flow

desktop publishing


flush

justify

margins

ragged


folder

desktop

directory

file

graphical user interface (GUI)


font

bit-mapped graphics

fixed pitch

font cartridge

font family

kerning

Page Description Language (PDL)

pitch

point

PostScript

proportional pitch

scalable font

soft font

TrueType

typeface

vector graphics


font cartridge

cartridge

download

font

laser printer

soft font


font family

font

typeface


footer

header


footprint

desktop model computer

tower model


forced page break

hard

page break

soft


foreground

background

multiprocessing


form feed

ASCII


format

controller

disk

hard disk

initialize

interleaving

low-level format

MFM

RLL

sector


formula

cell

constant

expression

spreadsheet


FORTRAN

ANSI

high-level language

ISO

programming language


forum

bulletin board system (BBS)

conference

online service

USENET


fourth-generation language

database management system (DBMS)

natural language

programming language

query

query language


fps

AVI

NTSC


FPU

coprocessor

floating-point number

Intel microprocessors


fragmentation

cluster

disk optimizer

file allocation table (FAT)


freeware

public-domain software

shareware


friction feed

printer

sheet feeder

tractor feed


front end

client/server architecture

compiler

distributed processing

user interface


frozen

crash


FTP

communications

Internet


full duplex

communications

half duplex

modem


function

command

library

procedure

program

routine


function keys

Alt key

Enhanced Keyboard

keyboard


fuzzy logic

artificial intelligence

Boolean logic

expert system

spell checker


G

giga (G)


gas-plasma display

flat-panel display

LCD

notebook computer


gateway

network


GDI printer

PCL

PostScript

printer

Windows


GEM

graphical user interface (GUI)

Macintosh computer

Microsoft Windows


genlock

composite video


GIF

data compression

graphics file formats


giga (G)

binary

mass storage

megabyte


gigabyte

byte

giga (G)

megabyte


glitch

bug


gopher

Archie

Internet

World Wide Web


gppm

laser printer

ppm


grabber

cursor


graphical user interface (GUI)

character based

desktop

drag-and-drop

icon

Macintosh computer

Microsoft Windows

pointer

pointing device

user interface


graphics

bit map

bit-mapped graphics

CAD

CAD/CAM

character based

clip art

CPU

desktop publishing

display screen

graphics file formats

laser printer

Microsoft Windows

monitor

personal computer

plotter


graphics accelerator

accelerator board

CPU

DRAM

graphics

multimedia

PCI

video adapter

VRAM


graphics based

character based


graphics character

block graphics

character mode

extended ASCII


graphics coprocessor

coprocessor

graphics accelerator


graphics display system

graphics

monitor

video adapter


graphics file formats

BMP

CGM

DXF

EPS

GEM

GIF

graphics

HPGL

IGES

PCX

PIC

PICT file format

TIFF

WMF


graphics mode

character based

graphics based

pixel

video adapter


graphics monitor

graphics

monitor


gray scaling

continuous tone

data compression

dithering

monitor

optical scanner


greeking

layout

preview


green PC

Energy Star

sleep mode


Group 3 protocol

CCITT

fax machine


Group 4 protocol

CCITT

fax machine

ISDN


groupware

e-mail

local-area network (LAN)

scheduler

workgroup computing


gutter

desktop publishing


GW-BASIC

BASIC


hack

kludge


hacker

programmer


half duplex

communications

full duplex

modem


half height

bay


halftone

continuous tone

desktop publishing

dithering

moiré


hand-held computer

handwriting recognition

notebook computer

palmtop

PDA

PIM


handle

chat

graphics

online service

pointer


handshaking

communications

protocol


handwriting recognition

hand-held computer

PDA

pen computer


hang

abort

bomb

bug

crash


hanging indent

word processing


hard

hardware

hardwired

software


hard card

bay

controller

expansion board

expansion slot

hard disk


hard copy

hard

soft


hard disk

cache

cylinder

disk drive

disk pack

Enhanced IDE

floppy disk

hard card

hard disk type

IDE interface

interleaving

mass storage

platter

removable hard disk

track


hard disk drive

disk drive

hard disk


hard disk type

BIOS

hard disk


hard return

return

soft return


hardware

firmware

hard

software


hardwired

constant

hard


Hayes compatible

AT command set

communications

de facto standard

modem


head

disk drive

head crash

platter


head crash

crash

disk

disk drive

head


header

footer

word processing


helical-scan cartridge

DAT

mass storage

tape


Help

context sensitive

documentation

FAQ


Hercules graphics

MDA

video adapter


heterogeneous network

local-area network (LAN)

network


hexadecimal

binary

decimal

octal


hidden file

attribute

file management system


hierarchical

directory

file management system

tree structure


high memory

conventional memory

DOS

expanded memory

extended memory

TSR


high memory area

extended memory


high-density disk

density

floppy disk


high-level language

Ada

assembly language

BASIC

C

C++

COBOL

compile

FORTRAN

LISP

low-level language

machine language

object-oriented programming (OOP)

Pascal

programming language


highlight

select


home computer

multimedia

personal computer


Home key

keyboard


home page

web site


host

remote control


hot key

control character

function keys

memory resident

TSR


hot link

database

link

OLE

spreadsheet


hot spot

multimedia


HP-compatible printer

compatible

driver

emulation

font cartridge

laser printer

PCL

PostScript


HPGL

PCL

plotter


HTML

browser

hypertext

JavaScript

SGML

World Wide Web


HyperCard

authoring tool

hypertext


hypertext

authoring tool

Help

HTML

HyperCard

multimedia

SGML


hyphenation

word processing

word wrap


I-beam pointer

insertion point

pointer


I/O

input

output


IBM PC

compatible

PC


icon

graphical user interface (GUI)


IDE interface

EIDE

hard disk drive

interface

SCSI

ST-506 interface


identifier

name

variable


IEEE

Ethernet

floating-point number

network

token-ring network


IGES

ANSI

graphics file formats


image editor

image enhancement

paint program

photo illustration


image enhancement

image editor

photo illustration


imagesetter

desktop publishing

Linotronic

PostScript

service bureau


ImageWriter

dot-matrix printer

LaserWriter

letter quality (LQ)

Macintosh computer

printer


impact printer

daisy-wheel printer

dot-matrix printer

ink-jet printer

laser printer

line printer

non-impact printer

printer


import

comma-delimited

convert

export

filter


inclusive OR operator

Boolean operator


increment

decrement

loop


incremental backup

archival backup

backup


Indeo

Cinepak

codec

DVI

MPEG


Industry Standard Architecture (ISA) bus

AT bus

bus

local bus

PCI

plug-and-play


information highway

bulletin board system (BBS)

online service

telecommunications


initialize

assign

format

variable


ink-jet printer

color printer

download

dpi

font

font cartridge

laser printer

printer

solid ink-jet printer


input

I/O

output


input device

device

I/O

light pen

mouse

output

trackball


Ins key

Insert key


insert

append

Ins key

insert mode


Insert key

insert mode


insert mode

Ins key

insertion point

overstrike

word processing


insertion point

I-beam pointer

insert mode

pointer


instruction

CISC

command

machine language

RISC


integer

character string

data type

floating-point number


integrated circuit (IC)

chip

semiconductor


Intel microprocessors

bus

clock speed

microprocessor

multitasking

OverDrive

Pentium Pro

register

RISC

virtual memory


Intellifont

Page Description Language (PDL)

PCL

scalable font


intelligent terminal

display screen

dumb terminal

monitor

smart terminal

terminal


interactive

batch processing


interface

user interface


interlacing

CRT

monitor

refresh

resolution


interleaved memory

access time

cache

clock speed

CPU

dynamic RAM

memory

page-mode memory

wait state


interleaving

disk

disk drive

sector

track


internal command

command

DOS

external command


internal modem

expansion board

external modem

modem


Internet

ARPANET

domain

FTP

gopher

InterNIC

intranet

IP address

Mbone

Mosaic

online service

USENET

World Wide Web


Internet Message Access Protocol

POP


InterNIC

domain name

Internet

IP address


interpreter

BASIC

compile

compiler

Java

LISP

Page Description Language (PDL)

PostScript

programming language


interprocess communication (IPC)

DDE

multiprocessing

network

operating system

process


intranet

firewall

Internet

network


invocation

invoke


invoke

call

function

routine


IP address

DNS

domain name

Internet

InterNIC

TCP/IP


IrDA

parallel port


IRMA board

emulation

expansion board

mainframe

stand-alone

terminal


IRQ

DIP switch

expansion bus

Industry Standard Architecture (ISA) bus

plug-and-play


ISA bus

AT bus

EISA


ISDN

broadband ISDN (B-ISDN)

FDDI

fiber optics

Group 4 protocol


ISO

ANSI

network

standard


italic

font


iteration

loop


jaggies

antialiasing

smoothing


Java

ActiveX

applet

C++

CGI

interpreter

JavaScript

object-oriented programming (OOP)

programming language


JavaScript

HTML

Java

script


job

program

task


join

database

field

query

relational database


joystick

mouse

pointer


JPEG

data compression

motion-JPEG

MPEG


jumper

configuration

configure

expansion board


justification

alignment

feathering

leading

microspacing

vertical justification


justify

flush

justification


KB

kilobyte


Kbps

data transfer rate

modem


Kermit

CCITT

communications

communications software

full duplex

MNP

modem

protocol

Xmodem

Zmodem


kerning

desktop publishing

font

word processing


key

database management system (DBMS)

encryption

field

password


keyboard

ADB

alphanumeric

Alt key

arrow keys

Backspace key

Break key

Caps Lock key

Control key

cursor

Delete key

Dvorak keyboard

End key

Enhanced Keyboard

Enter key


keyword

command

parameter

variable


kilobyte

binary

byte

giga (G)

megabyte

memory


kludge

hack


label

cell

disk

mass storage

name

spreadsheet

volume


landscape

monitor

portrait

printer

word processing


language

artificial intelligence

fourth-generation language

machine language

natural language

programming language

syntax


laptop computer

notebook computer

portable


large-scale integration (LSI)

chip

integrated circuit (IC)

VLSI


laser printer

color printer

font cartridge

HP-compatible printer

ink-jet printer

LCD printer

offset printing

Page Description Language (PDL)

PCL

PostScript

printer

resident font

resolution enhancement

smoothing

soft font

toner


LaserWriter

ImageWriter

laser printer

Macintosh computer

PostScript

printer

QuickDraw


launch

execute

load

run


layout

database management system (DBMS)

desktop publishing

field

report writer

word processing

WYSIWYG


LCD

active matrix display

backlighting

electroluminescent display (ELD)

flat-panel display

gas-plasma display

LCD printer

LED

notebook computer

supertwist

TFT


LCD printer

laser printer

LCD

pixel


leading

font

justification

point

vertical justification


leaf

hierarchical

node

tree structure


learn mode

macro


leased line

telecommunications


LED

laser printer

LCD


left justify

flush

justify


legend

presentation graphics


letter quality (LQ)

daisy-wheel printer

dot-matrix printer

draft quality

ink-jet printer

laser printer

near letter quality

printer


library

linker

module

object code

routine


light bar

highlight

menu

reverse video


light pen

CAD/CAM

display screen

input device

mouse

pixel

pointer


LIM memory

EEMS

expanded memory

extended memory


line editor

editor


line feed

ASCII

carriage return

off-line


line graph

bar chart

pie chart

presentation graphics


line printer

impact printer

printer


link

bind

cell

channel

communications

compile

database management system (DBMS)

filename

hot link

linker

OLE

path

record

spreadsheet

UNIX


link edit

linker


linker

address

compile

executable file

module

object code


Lino

imagesetter

Linotronic


Linotronic

imagesetter

PostScript

service bureau


LISP

artificial intelligence

high-level language

interpreter

programming language


listing

printout

source code


load

loader

main memory

operating system

program

register

traffic


loader

load

main memory

program

utility

virtual memory


local

local-area network (LAN)

network

node

remote

workstation


local bus

bus

expansion bus

PCI

VL-Bus


local-area network (LAN)

AppleTalk

ARCnet

client/server architecture

e-mail

Ethernet

NetWare

network

network interface card (NIC)

network operating system (NOS)

node

peer-to-peer architecture

personal computer

protocol

token-ring network

topology

TOPS


local-area wireless network (LAWN)

local-area network (LAN)


LocalTalk

AppleTalk

Ethernet

local-area network (LAN)

Macintosh computer

TOPS


lock

database management system (DBMS)

file

local-area network (LAN)

multi-user

operating system

record

write-protect


log on

access code

password

username


logical

fragmentation

physical


look-and-feel

user interface


loop

iteration


lossless compression

data compression

lossy compression

PKZIP


lossy compression

data compression

JPEG

lossless compression


Lotus 1-2-3

spreadsheet


low-level format

controller

format

interleaving


low-level language

assembly language

high-level language

language

machine language

programming language


lowercase

case sensitive

uppercase


LPT

printer


machine address

address


machine dependent

application


machine independent

machine dependent


machine language

assembly language

low-level language


machine readable

optical character recognition


Macintosh computer

Apple Computer

graphical user interface (GUI)

PowerPC


macro

batch file

command

dBASE

link

loop

program


magneto-optical (MO) drive

CD-ROM

hard disk

mass storage


mail merge

merge


mailbox

e-mail


main memory

address space

chip

conventional memory

dynamic RAM

expanded memory

expansion board

extended memory

loader

megabyte

memory

RAM

swap

virtual memory


mainframe

computer

microprocessor

minicomputer

supercomputer


manual recalculation

recalculate


map

compile

debug

load

option

programming language


MAPI

API

e-mail


margins

flush

word processing

word wrap


mask

field


mass storage

DAT

disk

disk drive

erasable optical disk

floppy disk

gigabyte

hard disk

kilobyte

magneto-optical (MO) drive

main memory

megabyte

memory

optical disk

random access

tape


mathematical expression

expression


matrix

array

background


maximize

graphical user interface (GUI)

window

zoom


Mbone

Internet

multimedia


MCGA

CGA

EGA

graphics

MDA

monitor

VGA

video standards


MDA

graphics

Hercules graphics

monitor

monochrome

pixel

resolution

VGA

video standards


media

disk

fiber optics

local-area network (LAN)

mass storage

multimedia

network


mega

giga (G)

kilobyte

megabyte


megabyte

byte

gigabyte

kilobyte


membrane keyboard

keyboard


memory

address

chip

EEPROM

EPROM

main memory

PROM

RAM

ROM

virtual memory

VRAM


memory effect

NiCad battery pack


memory resident

memory

operating system

swap

TSR


menu

choose

command driven

graphical user interface (GUI)

user interface


menu bar

menu

window


menu driven

command driven

menu

user interface


merge

mail merge


MFLOP

floating-point number

MIPS


MFM

controller

disk drive

RLL

ST-506 interface


MHz

bus

clock speed

microprocessor


micro

microfloppy disk


Micro Channel Architecture (MCA)

AT bus

bus

local bus


micro-justification

microspacing


microfloppy disk

density

disk

floppy disk


microprocessor

bandwidth

chip

CISC

clock speed

CPU

Intel microprocessors

Motorola microprocessors

Pentium Pro

PowerPC

RISC


Microsoft Windows

DOS

graphical user interface (GUI)

Intel microprocessors

operating system

OS/2

Windows 95

Windows NT


microspacing

justification

printer


MIDI

Amiga

Macintosh computer

sound card


millisecond

access time


minicomputer

computer

mainframe

multi-user

workstation


minifloppy

floppy disk


minimize

graphical user interface (GUI)

icon

window


MIPS

CPU

MFLOP


MIS

COBOL

mainframe

minicomputer


MNP

communications protocol

data compression

error detection

Kermit

modem

Xmodem


mode

insert mode

overstrike


modem

bps

CCITT

communications

communications protocol

communications software

data compression

flash memory

Hayes compatible

MNP

RS-232C


modifier key

keyboard


Modula-2

compile

multitasking

Pascal

programming language


modular architecture

architecture

integrated

module


module

link

modular architecture

program

routine


moiré

halftone


monitor

analog monitor

background

bandwidth

color monitor

convergence

digital monitor

display screen

dot pitch

dpi

fixed-frequency monitor

flat technology monitor

gray scaling

interlacing

monochrome

multiscanning monitor

pixel

refresh


monochrome

background

foreground

graphics

gray scaling

monitor


monospacing

Courier font

font

proportional spacing


Mosaic

browser

Internet

World Wide Web


motherboard

add-on

BIOS

bus

controller

CPU

expansion board

expansion slot

microprocessor

port

printed circuit board


motion-JPEG

JPEG

MPEG


Motorola microprocessors

CISC

microprocessor

PowerPC

RISC


mouse

ADB

bus

bus mouse

click

cursor

double click

ergonomics

expansion board

graphical user interface (GUI)

menu driven

pointer

serial port

trackball


mousepad

mouse


moving-bar menu

menu


MPC

CD-ROM

CD-ROM player

Intel microprocessors

multimedia


MPEG

codec

data compression

DVI

fps

Indeo

JPEG


ms

mass storage


MTBF

disk drive


multi-user

mainframe

minicomputer


MultiFinder

clipboard

desktop

Finder

Macintosh computer

multitasking

operating system


multifrequency monitor

monitor

multiscanning monitor

video adapter


multimedia

3DO

animation

authoring tool

CD-ROM

hypertext

Mbone

media

MPC


multiprocessing

CPU

distributed processing

interprocess communication (IPC)

multitasking

OS/2

parallel processing

process

UNIX


multiscanning monitor

analog monitor

digital monitor

fixed-frequency monitor

multifrequency monitor

video adapter

video standards


multitasking

cooperative multitasking

MultiFinder

multiprocessing

operating system

OS/2

UNIX


multithreading

multitasking


name

alias

domain name

extension

filename

identifier

label

variable


nanosecond

access time


natural language

artificial intelligence

fourth-generation language

language


near letter quality

dot-matrix printer

draft mode

draft quality

letter quality (LQ)

printer


Net

Internet


NetBIOS

API

BIOS

local-area network (LAN)


netiquette

forum

Internet


NetWare

Ethernet

local-area network (LAN)

operating system

token-ring network


network

backbone

client/server architecture

communications

Ethernet

firewall

heterogeneous network

intranet

local-area network (LAN)

protocol

server

token-ring network

topology

wide-area network (WAN)


network interface card (NIC)

expansion board

local-area network (LAN)

media

network

protocol


network operating system (NOS)

local-area network (LAN)

operating system


neural network

artificial intelligence

digital

voice recognition


newbie

online service


NextStep

Apple Computer

object oriented

operating system


NiCad battery pack

battery pack

memory effect

NiMH battery pack

notebook computer


NiMH battery pack

battery pack

memory effect

NiCad battery pack


node

leaf

network

tree structure


noise

communications

fiber optics


non-impact printer

impact printer

ink-jet printer

laser printer

printer


non-interlaced

interlacing

monitor

screen flicker


non-volatile memory

memory

RAM

ROM


NOR operator

Boolean operator


NOT operator

Boolean operator


notebook computer

active matrix display

backlighting

battery pack

hand-held computer

PDA

slate PC

subnotebook computer

VGA


NSFnet

ARPANET

network

wide-area network (WAN)


NTSC

composite video

interlacing

RGB monitor

video adapter


NuBus

expansion bus

Macintosh computer

PCI


null character

character string

padding


null-modem cable

modem

port

RS-232C


Num Lock key

cursor control keys

numeric keypad

toggle


number cruncher

supercomputer

workstation


numeric keypad

arrow keys

keyboard

mode

Num Lock key


object

object oriented

object-oriented graphics

object-oriented programming (OOP)

OLE


object code

assembler

assembly language

code

compile

library

link

load

machine language


object oriented

object-oriented programming (OOP)

vector graphics


object-oriented graphics

bit-mapped graphics

graphics

PostScript

scalable font

vector graphics


object-oriented programming (OOP)

C++

class

component software

Java

object oriented


octal

binary

decimal

hexadecimal


ODBC

database management system (DBMS)

driver

query

SQL


odd header

header


odd parity

parity checking


off-line

form feed

on-line


office automation

e-mail

network

word processing


offset

address

base address

desktop publishing

gutter

relative address


OLE

ActiveX

applet

Component Object Model

component software

DDE

embedded object

hot link

link

object oriented

OpenDoc


on-board

expansion board

motherboard

on-board modem

printed circuit board


on-board modem

modem


on-line

off-line

printer


online service

America Online

bulletin board system (BBS)

chat

CompuServe Information Service

forum

Internet


OOPL

object-oriented programming (OOP)


open

close

file

operating system


open architecture

add-on

architecture

clone

proprietary

standard


OpenDoc

Component Object Model

component software

compound document

OLE


operand

expression

operator


operating environment

control program

environment

graphical user interface (GUI)

Microsoft Windows

operating system

shell


operating system

application

BIOS

command processor

DOS

file management system

Microsoft Windows

multi-user

multiprocessing

multitasking

multithreading

OS/2

UNIX


operator

Boolean operator

expression

operand

precedence

relational operator


optical character recognition

ASCII

font

optical scanner

printed circuit board


optical disk

CD-I (Compact Disc-Interactive)

CD-ROM

compact disc

disk

erasable optical disk

mass storage

ROM

WORM (write-once, read many)


optical scanner

ASCII

bit map

CCD

color depth

fax machine

flatbed scanner

font

gray scaling

optical character recognition

resolution

TWAIN


option

command

command driven

dialog box

graphical user interface (GUI)

menu


Option key

Alt key

keyboard

Macintosh computer


OR operator

Boolean operator


orphan

pagination

widow

word processing


OS/2

DOS

graphical user interface (GUI)

Microsoft Windows

multitasking

operating system

PC


outline font

bit map

font

PostScript

resolution

scalable font

TrueType

typeface

vector graphics


output

I/O


output device

device

output


OverDrive

Intel microprocessors


overlaid windows

pop

push

tiled windows

window


overwrite mode

insert mode


pack

data compression

packed file


packed file

data compression

modem


pad character

database

field

null character


padding

pad character


page

main memory

page-mode memory

paging

segment

swap

virtual memory


page break

hard

soft

word processing


Page Description Language (PDL)

laser printer

object oriented

PCL

PostScript


page layout program

desktop publishing

kerning

text flow

word processing


page printer

laser printer

Page Description Language (PDL)

printer


page-mode memory

CPU

interleaved memory

memory

RAM

wait state


page-white display

flat-panel display

LCD

supertwist


pagination

orphan

widow

word processing


paging

demand paging

main memory

operating system

page

segment

swap

virtual memory


paint program

bit-mapped graphics

draw program

graphics

vector graphics


palette

draw program

EGA

graphics

paint program

video adapter


palmtop

hand-held computer

notebook computer

PDA

portable


Pantone Matching System (PMS)

CMYK

color management system (CMS)

process colors

spot color


paper feed

printer

tractor feed


paper-white display

display screen

monitor


paperless office

fax machine

optical character recognition

workgroup computing


parallel

parallel port

port

printer

serial


parallel interface

Centronics interface

channel

parallel

parallel port

serial port


parallel port

Centronics interface

ECP

EPP

IrDA

LocalTalk

parallel

port

SCSI

serial port


parallel processing

CPU

distributed processing

multitasking


parameter

argument

routine


parent directory

directory

root directory


parity

parity checking


parity checking

CCITT

communications

communications protocol

MNP

modem


park

disk drive

head

head crash


partition

disk drive

Finder


Pascal

high-level language

Modula-2

programming language


passive-matrix display

active matrix display

flat-panel display

LCD

pixel

TFT


password

access code

key

log on

security


paste

buffer

clipboard

copy

cut

embedded object

link

OLE


patch

bug

executable file

object code


path

directory

DOS

executable file

pathname

working directory


pathname

directory

filename

root directory

working directory


pattern recognition

handwriting recognition

optical character recognition

voice recognition


Pause key

scroll


PC

clone

compatible

expansion bus

IBM PC

local bus

Macintosh computer

operating system

personal computer

printed circuit board

video standards


PC card

PCMCIA


PC-DOS

DOS


PCI

bus

expansion bus

Industry Standard Architecture (ISA) bus

local bus

NuBus


PCL

HP-compatible printer

HPGL

Intellifont

laser printer

Page Description Language (PDL)

PostScript

scalable font


PCMCIA

plug-and-play


PCX

bit-mapped graphics

BMP

graphics file formats

TIFF


PDA

Apple Computer

hand-held computer

handwriting recognition

palmtop

voice recognition


peer-to-peer architecture

client/server architecture

local-area network (LAN)


pen computer

hand-held computer

handwriting recognition

palmtop

PDA


Pentium microprocessor

Pentium Pro


Pentium Pro

Intel microprocessors

microprocessor


peripheral device

controller

device


personal computer

Amiga

clone

computer

home computer

Macintosh computer

microprocessor

PC

workstation


personal finance manager

accounting software


Phoenix BIOS

BIOS

clone


photo illustration

image enhancement


physical

fragmentation

hardware

logical

software

virtual memory


PIC

graphics

graphics file formats

Lotus 1-2-3


pica

point


PICT file format

graphics

graphics file formats

Macintosh computer

object oriented

QuickDraw


pie chart

presentation graphics


PIM

calculator

calendar

scheduler


pin

chip

connector

dot-matrix printer

letter quality (LQ)

near letter quality

printer


pipe

input

output


pipelining

Intel microprocessors

microprocessor

RISC


pitch

dot pitch

fixed pitch

font

monitor

proportional pitch


pixel

convergence

graphics

gray scaling

monitor

resolution

true color


PKZIP

data compression

shareware

ZIP


plain text

ASCII file


plasma display

flat-panel display

pixel


platform

environment


platter

hard disk


plot

plotter


plotter

CAD

printer


plug

connector


plug compatible

compatible

expansion board


plug-and-play

PnP


PnP

BIOS

expansion board

plug-and-play


point

font

graphical user interface (GUI)

leading

mouse

pointer

scalable font


pointer

address

graphical user interface (GUI)

I-beam pointer

variable


pointing device

input device

joystick

light pen

mouse

pointer

pointing stick

touchpad

trackball


pointing stick

joystick

pointing device

trackball


polling

modem


polyline

draw program


POP

e-mail

Internet Message Access Protocol

Simple Mail Transfer Protocol


pop

pop-up window

push

stack

window


pop-up utility

hot key

memory resident

TSR


pop-up window

graphical user interface (GUI)

pull-down menu

window


port

Centronics interface

COM

compile

connector

interface

machine dependent

parallel port

portable

serial port


portable

docking station

hand-held computer

machine independent

notebook computer

palmtop

PDA

subnotebook computer


portrait

landscape

monitor

printer


post

forum

USENET


PostScript

desktop publishing

EPS

laser printer

object-oriented graphics

Page Description Language (PDL)

service bureau


POTS

communications

ISDN


power supply

UPS


power user

user


PowerPC

Intel microprocessors

Macintosh computer

microprocessor

Motorola microprocessors

RISC


ppm

gppm

laser printer

printer


PPP

Internet

protocol

SLIP


PRAM

configure

control panel

Macintosh computer

memory

RAM


precedence

expression

operand

operator


precision

double precision

floating-point number


presentation graphics

bar chart

graphics

line graph

pie chart

spreadsheet


preview

greeking

thumbnail

word processing

WYSIWYG


primary cache

cache


primary storage

main memory

mass storage


Print Screen key

capture

hard copy


printed circuit board

chip

controller

expansion board

expansion slot

local-area network (LAN)

motherboard

video adapter


printer

daisy-wheel printer

dot-matrix printer

draft quality

font

graphics

impact printer

ink-jet printer

laser printer

LCD

LCD printer

LED

letter quality (LQ)

line printer

near letter quality

page printer


printer driver

driver


printer engine

printer


procedure

function

routine


process

task


process colors

CMYK

color separation

offset printing


processor

CPU

microprocessor


Prodigy

online service


program

algorithm

assembler

assembly language

code

compiler

executable file

high-level language

instruction

interpreter

language

low-level language

machine language

module

programming language

software


programmer

hacker

program

PROM


programming language

assembly language

BASIC

C

C++

COBOL

compiler

FORTRAN

fourth-generation language

high-level language

interpreter

Java

language

LISP

low-level language

machine language

Modula-2

object-oriented programming (OOP)

Pascal


PROM

EEPROM

EPROM

main memory

memory

ROM


prompt

time-out


proportional font

font

pitch

proportional pitch


proportional spacing

fixed pitch

font

monospacing

pitch


proprietary

architecture

open architecture

standard


protected mode

DOS

extended memory

Intel microprocessors

Microsoft Windows

multitasking

OS/2

UNIX

virtual memory


protocol

CCITT

communications

communications protocol

handshaking

modem


public carrier

e-mail


public-domain software

freeware

shareware


pull-down menu

command

menu

option

pop-up window


purge

delete


push

pop

stack


push-button

dialog box


QIC

mass storage

tape


quad-speed CD-ROM drive

CD-ROM player


query

database management system (DBMS)

field

join

menu

query by example

query language

record


query by example

database management system (DBMS)

field

query

query language

record


query language

database management system (DBMS)

query

SQL


queue

buffer

data structure

job

operating system

spooling

stack


QuickDraw

graphics

LaserWriter

Macintosh computer

pixel

PostScript

scalable font


QuickTime

animation

AVI

Cinepak

codec

Indeo

multimedia


QWERTY keyboard

Dvorak keyboard

keyboard


radio buttons

button

check box

graphical user interface (GUI)

select


ragged

flush

justify


RAM

dynamic RAM

main memory

memory

ROM

SRAM

VRAM


RAM cache

cache

disk cache


RAM disk

disk

extended memory

RAM


random access

access

RAM

sequential access


range

cell

expression

function

spreadsheet


raster image processor (RIP)

bit map

PostScript

vector graphics


raw data

data


ray tracing

graphics


RDBMS

database management system (DBMS)

relational database


read

access


read-only

attribute

CD-ROM

read/write

ROM


read/write

read-only


real mode

DOS

extended memory

Intel microprocessors

Microsoft Windows

multitasking

OS/2

protected mode

virtual memory


real time

operating system


real-time clock

clock speed

CPU


reboot

boot


recalculate

automatic recalculation

background

cell

formula

spreadsheet


record

data structure

data type

database

database management system (DBMS)

field

file


recursion

program

programming language


redirection

default

device

DOS

file

I/O

operating system

operator

shell

UNIX


redlining

word processing


refresh

dynamic RAM

interlacing

monitor

screen flicker


register

compiler

CPU

load

microprocessor

software piracy


relational database

database

database management system (DBMS)

flat-file database

query


relational operator

Boolean logic

expression

operator


relative address

absolute address

address

base address

cell

memory

offset


relative cell reference

absolute cell reference

cell

spreadsheet


remote

local

local-area network (LAN)

network

workstation


remote control

host

local

remote


removable hard disk

cartridge

disk

disk pack

hard disk

mass storage


rendering

ray tracing


repaginate

orphan

page break

widow


report

report writer


report writer

database management system (DBMS)

field

record


reserved word

keyword

variable


reset button

boot

hang

reboot


resident font

download

font

font cartridge

printer

soft font


resolution

bit map

dpi

monitor

pixel

printer

video adapter


resolution enhancement

laser printer

printer engine

resolution


restore

graphical user interface (GUI)

size

window

zoom


return

carriage return

hard return

Return key

soft return


Return key

cursor

Enter key

hard return

insertion point

keyboard

prompt


reverse video

background

display screen

foreground


RGB monitor

color monitor

composite video

convergence

monitor


rich text format (RTF)

HTML

SGML

World Wide Web


ring network

local-area network (LAN)

token-ring network

topology


RISC

CISC

CPU

instruction

microprocessor


RLL

controller

disk drive

MFM


robotics

artificial intelligence

CAM


ROM

BIOS

boot

EEPROM

firmware

memory

PROM

RAM


roman

font

italic


root directory

directory

file management system

hierarchical


router

gateway


routine

function

module

program


RS-232C

connector

interface

modem

RS-422 and RS-423

serial port


RS-422 and RS-423

communications

connector

interface

modem

port

RS-232C


rule

expert system


ruler

desktop publishing

margins

page layout program


run

launch


runtime error

bomb

bug

compiler

crash


sampling

analog

digital

digital camera

digitize


sans serif

font


save

autosave

close


scalable font

font

Intellifont

outline font

PostScript

TrueType

typeface

vector graphics


scale

graphics

scalable font

vector graphics


scheduler

calendar

groupware

operating system

workgroup computing


scientific notation

floating-point number


Scrapbook

clipboard

desk accessory (DA)


screen capture

capture

Print Screen key


screen flicker

interlacing

monitor

refresh


screen font

font

resolution


screen saver

display screen

monitor


script

batch file

HyperCard

JavaScript

macro


scroll

page

scroll bar


scroll bar

click

drag

graphical user interface (GUI)

window


Scroll Lock key

cursor control keys

scroll


SCSI

bus

daisy chain

interface

port


search and replace

character string

word processing


secondary cache

cache

Pentium microprocessor

Pentium Pro

primary cache


sector

bad sector

disk

format

interleaving

track


security

audit trail

encryption

firewall

password


seek time

access time

disk drive


segment

main memory

page

swap

virtual memory


select

block

choose

drag

graphical user interface (GUI)

highlight

icon

pointer


semantics

programming language

syntax


semiconductor

chip

CMOS

integrated circuit (IC)


sequential access

random access


serial

communications

parallel

serial port


serial mouse

mouse

port

serial

serial port


serial port

communications

interface

parallel port

port

RS-232C

RS-422 and RS-423


serif

font

sans serif

typeface


server

client/server architecture

local-area network (LAN)

network


service bureau

desktop publishing

imagesetter

Linotronic

offset printing

PostScript


service provider

e-mail

Internet

USENET

World Wide Web


SGML

HTML

hypertext

ISO

rich text format (RTF)

World Wide Web


shadowing

BIOS

boot

main memory

RAM

ROM


shareware

bulletin board system (BBS)

freeware

online service

public-domain software

software piracy


sheet feeder

dot-matrix printer

fax machine

laser printer

optical scanner

printer


shell

command driven

command language

command processor

interface

menu driven

operating environment

operating system

UNIX

user interface


shift clicking

click

graphical user interface (GUI)

Macintosh computer

Microsoft Windows

mouse

select


Shift key

Alt key

Control key

keyboard


shortcut key

Alt key

command

Control key


SIG

bulletin board system (BBS)

forum

online service


sign

operator


Silicon Valley

chip

semiconductor


SIMM

chip

RAM


Simple Mail Transfer Protocol

POP


Simple Network Management Protocol

Internet Message Access Protocol

POP


single-density disk

floppy disk


single-sided disk

floppy disk


SIP

DIP

PGA


size

graphical user interface (GUI)

scale

window


slate PC

hand-held computer

handwriting recognition

notebook computer

PDA


sleep mode

green PC


SLIP

Internet

PPP

protocol

service provider


slot

bay

cartridge

chassis

expansion board

expansion slot

printed circuit board


smart terminal

dumb terminal

intelligent terminal

terminal


smoothing

antialiasing

jaggies

laser printer


soft

hard

hardware

software


soft font

download

font

font cartridge

laser printer

resident font


soft return

hard return

margins

word wrap


software

application

data

firmware

hardware

program

systems software


software piracy

copy protection

register

shareware

software


solid ink-jet printer

color printer

ink-jet printer


sound card

CD-ROM

MIDI

multimedia


source

copy

destination


source code

assembler

code

compiler

machine language

object code

program

programming language


special character

control character


speech synthesis

voice recognition


spell checker

word processing


split screen

window


spooler

queue

spooling


spooling

background

buffer

queue


spot color

color separation

Pantone Matching System (PMS)

process colors


spreadsheet

cell

formula

label

Lotus 1-2-3

three-dimensional spreadsheet


SQL

database management system (DBMS)

distributed database

query

query language


SRAM

access time

cache

cycle time

dynamic RAM

RAM


ST-506 interface

hard disk

IDE interface

interface

MFM

RLL

SCSI


stack

data structure

HyperCard

pop

push

queue


stand-alone

fax machine


standard

ANSI

architecture

CCITT

compatible

de facto standard

IEEE

ISO

open architecture

VESA


standard input

input


standard output

output


star network

local-area network (LAN)

topology


start bit

asynchronous

bit

byte


statement

expression

programming language


static variable

dynamic variable

variable


stop bit

asynchronous

bit

byte


storage

mass storage


storage device

disk drive

mass storage

tape drive


strikeout

workgroup computing


style

format

style sheet


style sheet

desktop publishing

font

layout

margins

style

word processing


stylus

digitizing tablet

touch screen


subdirectory

directory

folder

root directory


subnotebook computer

hand-held computer

notebook computer

portable


subscript

array

superscript

word processing


supercomputer

computer

mainframe


SuperDrive

FDHD

floppy disk

Macintosh computer


superscript

subscript

word processing


supertwist

background

backlighting

flat-panel display

LCD

notebook computer


support

customer support


surf

browse

World Wide Web


surge protector

UPS


SVGA

8514/A

palette

resolution

VESA

VGA

video standards


swap

demand paging

main memory

memory

operating system

page

paging

process

segment

UNIX

virtual memory


swap file

swap


switch

DIP switch

option

parameter

toggle


synchronous

asynchronous

bus

clock speed


syntax

language

semantics


sysop

bulletin board system (BBS)

network

SIG


System

Finder

Macintosh computer

operating system


system call

invoke

operating system

routine


System folder

Finder

folder

Macintosh computer

system


systems analyst

programmer


systems software

application

end user

software

utility


tab character

Tab key

tab stop


Tab key

cell

cursor

field

insertion point

tab character

tab stop


tab stop

tab character

Tab key


table

database management system (DBMS)

relational database

spreadsheet


tablet

digitizing tablet


tape

backup

DAT

disk drive

helical-scan cartridge

mass storage

QIC

sequential access


tape drive

backup

tape


target

source


task

job

multitasking

multithreading

operating system


task switching

DOS

multitasking

operating environment

operating system


TCP/IP

communications

Internet

IP address

NetWare

protocol

Winsock


tear-off menu

menu


telecommunications

communications


telecommuting

e-mail

network

workgroup computing


telecopy

fax machine


Telenet

online service

wide-area network (WAN)


template

boilerplate

command buffer

cursor

digitizing tablet


terabyte

gigabyte

megabyte


terminal

console

display screen

dumb terminal

emulation

intelligent terminal

keyboard

monitor

network

smart terminal


terminal emulation

bulletin board system (BBS)

emulation

mainframe

terminal


Texas Instruments Graphics Architecture (TIGA)

8514/A

graphics

SVGA

TI 34010

VESA

video standards

XGA


text

ASCII


text file

ASCII

file

text


text mode

character based

graphics based

graphics mode

video mode

video standards


text wrap

word processing


TFT

active matrix display

flat-panel display

LCD


thermal printer

fax machine

printer


thread

forum

multithreading

online service


three-dimensional spreadsheet

spreadsheet


throughput

disk drive

network


thumbnail

desktop publishing

greeking

layout


TI 34010

8514/A

interlacing

TIGA

video standards


TIFF

bit map

graphics

graphics file formats

gray scaling

PCX


tiled windows

cascading windows

overlaid windows

window


time sharing

mainframe

minicomputer

multi-user


time-out

interrupt


title bar

drag

window


toggle

DIP switch

keyboard

switch


token

keyword

operator

programming language

token-ring network


token-ring network

ARCnet

IEEE

local-area network (LAN)

network

token


toner

laser printer


topology

Ethernet

local-area network (LAN)


TOPS

AppleTalk

local-area network (LAN)

peer-to-peer architecture


touch screen

display screen

light pen

mouse

point


touchpad

digitizing tablet

pointing device


tower model

chassis

desktop model computer


TPI

disk

track


track

cylinder

format

hard disk

interleaving

sector


trackball

mouse

pointing device


tractor feed

friction feed

printer


traffic

load


transaction processing

batch processing


transportable

laptop computer

notebook computer

portable


tree structure

branch

data structure

directory

hierarchical

leaf


TrueType

font

outline font

PostScript


truncate

floating-point number


TSR

hot key

memory resident

multitasking

operating system


TTL monitor

analog monitor

digital monitor

MDA


turnkey system

OEM


TWAIN

driver

optical scanner


twisted-pair cable

coaxial cable

fiber optics

local-area network (LAN)


Tymnet

network


typeface

font

font family


UART

asynchronous

serial port


ULSI

chip

Pentium microprocessor


underflow

floating-point number

overflow error


undo

command


undocumented

documentation


Unicode

ASCII

character

character set


UNIX

A/UX

AIX

C

multitasking

operating system

OS/2


unpack

data compression


upload

bulletin board system (BBS)

download

network

online service


uppercase

Caps Lock key

case sensitive

lowercase


UPS

power supply


upward compatible

backward compatible

compatible

DOS

downward compatible


URL

address

Internet

World Wide Web


USENET

bulletin board system (BBS)

forum

Internet


user

application

end user


user group

SIG


user interface

command driven

graphical user interface (GUI)

look-and-feel


user-friendly

graphical user interface (GUI)


username

bulletin board system (BBS)

multi-user

online service

password


utility

application

TSR


Uuencode

BinHex

e-mail


variable

character string

constant

data

data type

expression


variable length

database management system (DBMS)

field

fixed length

record


variable-length record

field

fixed length

record

variable length


VDT radiation

ELF emission

monitor


vector

array


vector graphics

autotracing

Bézier curve

bit map

bit-mapped graphics

CGM

draw program

graphics

graphics file formats

object oriented

PostScript

raster image processor (RIP)

scalable font


vertical justification

feathering

justification

leading

word processing


VESA

SVGA

VL-Bus


VGA

SVGA

video adapter


video adapter

8514/A

adapter

color depth

graphics accelerator

monitor

video mode

video standards

VRAM


Video for Windows

codec

MPEG

QuickTime


video mode

graphics mode

text mode

video adapter


video standards

8514/A

MCGA

MDA

SVGA

TI 34010

VGA

video adapter

XGA


videoconferencing

workgroup computing


view

database

database management system (DBMS)

field


viewer

file management system

format

shell


virtual

virtual memory


virtual memory

address space

main memory

memory

operating system

page

paging

swap

virtual


virtual reality

cyberspace

virtual


virus

ARPANET

hacker

network


VL-Bus

expansion bus

local bus

PCI


VLSI

chip

integrated circuit (IC)

ULSI


voice mail

e-mail


voice recognition

artificial intelligence

natural language


volatile memory

memory

RAM

ROM


volume

disk

mass storage


volume label

disk

label

volume


VRAM

graphics

graphics accelerator

memory

monitor

processor

RAM


WAIS

gopher

Internet


wait state

cache

clock speed

interleaving

page-mode memory


warm boot

boot

cold boot


web page

home page

URL

World Wide Web


web site

home page

World Wide Web


whitespace

null character


wide-area network (WAN)

Internet

network


widow

orphan

pagination

word processing


Winchester disk drive

disk drive

hard disk


window

dialog box

graphical user interface (GUI)

icon

Microsoft Windows


Windows 95

Microsoft Windows


Windows NT

Microsoft Windows

multitasking

operating system

preemptive multitasking

Windows


Winsock

API

TCP/IP


WMF

graphics

graphics file formats


word

bit

byte

CPU


word processing

copy

cut

delete

desktop publishing

editor

font

footer

graphics

header

hyphenation

insert

justify

layout

macro


word processor

word processing


word wrap

hard return

hyphenation

margins

soft return

word processing


WordPerfect

word processing


workgroup computing

e-mail

groupware


workgroup productivity package

calendar

e-mail

local-area network (LAN)

scheduler

workgroup computing


working directory

directory

pathname

root directory


workstation

CAD/CAM

computer

desktop publishing

diskless workstation

graphics

local-area network (LAN)

minicomputer

network

personal computer

UNIX


World Wide Web

browser

CGI

HTML

hypertext

Internet

Mosaic

surf

web site


WORM (write-once, read many)

CD-ROM

erasable optical disk

mass storage

optical disk


write

access

read


write-protect

diskette

lock


WYSIWYG

color matching

desktop publishing

font

PostScript

resolution

word processing

WYSIWYP


WYSIWYP

color management system (CMS)

color matching

WYSIWYG


x-height

ascender

baseline

descender

typeface


X-Windows

graphical user interface (GUI)

public-domain software

UNIX


Xenix

operating system

UNIX


XGA

8514/A

interlacing

resolution

SVGA

VGA

video standards


Xmodem

checksum

communications protocol

communications software

Kermit

modem

protocol

Ymodem

Zmodem


XMS

expanded memory

extended memory

high memory area


XOR operator

Boolean operator


Yahoo!

Alta Vista


Ymodem

batch processing

communications protocol

Xmodem

Zmodem


Zero Insertion Force (ZIF) socket

chip


zero wait state

wait state


ZIP

ARC

data compression


Zmodem

communications protocol

Kermit

Xmodem

Ymodem


zoom

box

graphical user interface (GUI)

maximize