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Text File | 1992-12-06 | 33KB | 553 lines

---------------------------------------------------------------- INTRODUCTION TO COMPUTER TECHNOLOGY - INPUT, STORAGE, OUTPUT ---------------------------------------------------------------- Before we examine computer technology let's cover two items which seem to confuse EVERY computer beginner. It's a wonder computer manufacturers don't include these two ESSENTIAL points in instruction books. First item: Booting. Many times an instruction manual refers to "booting up" or "booting DOS" before you can start a program. This means inserting your DOS diskette in a floppy drive and starting the machine with the DOS diskette in place. When you see the familiar A> or C> prompt symbol, you have booted up! If you have a hard drive which starts the machine automatically, the hard drive "boots DOS" for you and you do NOT need to use the DOS diskette. This seems simple, but many beginners are confused by the term "booting up." Second item: Working with floppy diskettes. A standard floppy diskette is either 5 1/4 inches or 3 and 1/2 inches square. To insert a floppy diskette into your computer drive, first remove it from the paper or plastic slipcover if one protects it. The proper way to insert a floppy diskette in most drives is as follows. For larger 5 - 1/4 inch floppies, turn the printed label side up and locate the TWO VERY TINY notches along one edge. Near the notches will be a jelly bean shaped hole about one inch long cut into the plastic surface of the diskette. This oblong hole is the read/write opening. Insert the diskette into the drive with the label side up and the two tiny notches FIRST into the drive opening then close the drive locking handle. Along one edge of the diskette you will also see a SINGLE square shaped hole which is the write protect notch. If this write protect notch is UNCOVERED you can BOTH read and write data to the diskette. If the write protect notch is covered with a piece of tape, then you can READ information from the diskette but you CANNOT write information to the diskette. This is a safeguard feature you may wish to use from time to time. Keep fragile diskettes away from smoke, hair, dirt and ESPECIALLY sources of magnetism such as motors, loudspeakers or even childrens magnetic toys which may ERASE your data! For smaller 3 - 1/2 inch size diskettes, turn the label side up and locate the metal "shutter". Insert the diskette into the drive with the label up and the shutter FIRST into the drive. The write protect notch or opening is a small square hole with a SLIDING PLASTIC TAB which is slid CLOSED (cannot see an open hole) to enable BOTH reading and writing to the diskette. The sliding tab is placed OPEN (visible open hole) to enable reading but NOT writing. Here is how to tell the different densities of various diskettes your computer might need: a standard 5 - 1/4 inch, 360K (Kilobyte) diskette has a plastic reinforcing ring around the center hole. A 1.2MB (Megabyte) diskette does not. Small 3 - 1/2 inch, 720K diskettes have one small notch cut in the plastic diskette casing while 1.44MB diskettes have two notches. Time to move on to basic computer technology . . . Computers vary widely in size and use. However all computers are similar in what the hardware does. So-called microcomputers (like your desktop pc) are designed for personal use, relatively low price, and modest data processing tasks. Minicomputers are moderate sized (a small refrigerator size) and perform more complex tasks with larger amounts of data. Minicomputers might be used in a small engineering office or a local bank branch to send transaction data to a head office computer. Mainframe computers are large, expensive and process billions of characters of data rapidly and fill entire rooms. Finally supercomputers are built to minimize distance between circuit boards and operate at very high speed for complex uses such as designing airplanes, animating complex movie sequences graphically or solving complex engineering formulas having billions of steps mathematically. Supercomputers are built for raw speed. Some terms apply to all computers. INPUT is how data gets into a computer. The keyboard and mouse are familiar INPUT devices. OUTPUT references how data is provided from the computer. A Monitor or printer are good examples of OUTPUT devices. PRIMARY STORAGE or MEMORY is the computer's immediate data storage area - usually this is in small integrated circuit chips which hold data ONLY while power is supplied. This PRIMARY STORAGE area is thus temporary. More permanent SECONDARY STORAGE is used when computer power is off or when data overflows primary storage. This is usually floppy or hard disk drives but can include paper tapes, punch cards, or even non-volatile magnetic bubble memories. How do computers store data and programs? For the PC (personal computer) storage of data can take place either in an integrated circuit chip or IC when the machine is on or a magnetic disk when the machine is turned off. The magnetic disk used to store information works in a manner similar to a tape recorder - magnetic impressions are placed on the tape and can be later replayed. Magnetic sound tape as a long strip of plastic with a thin coating of a metallic, easily magnetized powder glued to the surface of the plastic strip. When a electrically driven coil is placed near the surface of the plastic strip, thousands of little magnets are created on the surface of the tape as it rapidly streams beneath the coil. Later these little magnets can induce current to flow in the coil as the tape is pulled past the coil a second time. Thus the information or music is replayed. During recording, the electrical coil receives electric pulses which produce small magnetic "blips" along the tape. During playback, the coil is passive and the little magnetic pulses passing below its surface create electric pulses in the coil which are amplified. A magnetic computer disk works in the same fashion but spins in a circle like a music record rather than moving in a straight line like recording tape. Magnetic computer disks are available in two basic types: floppy and hard disks. A hard disk can hold considerably more information than a floppy disk - frequently millions of computer words (or "bytes") while a floppy disk holds less than a million in many cases. However what the floppy disk loses in capacity in gains in the advantage of portability since it can easily be removed from the pc and stored which is not true of the hard disk. On a typical music cassette tape you will find two channels (left and right speakers) and a total of four tracks (side A of the tape and side B.) Think of this as four lines of "information" running the length of the music tape. On a computer disk data is stored in a similar manner except there are far more tracks of information and of course the tracks are arranged in circles on a flat surface like a music record or compact CD disk. Tracks of computer information are written to and read from the computer disk by a read/write coil (head) that moves rapidly across the surface of the disk in a fashion similar to a record player needle on a music record. Most current disks (360K IBM format) have 40 tracks which are numbered from 0 to 39. The low numbers are towards the edge of the disk - the high numbers towards the center. Tracks, the circular data paths on the disk, are divided into still smaller units called sectors with the number of sectors varying with the exact DOS operating system you use on your PC. MS-DOS version 2.0 and higher versions use nine sectors per track. DOS 2.0 and above can read the older eight sector disks created by DOS version 1.1 but the reverse is not true. Each track is divided into the same number of sectors like pieces of apple pie. The sectors contain the magnetic bits or pulses of information which the computer records in a special index (called the file allocation table or FAT) so that it can quickly move from sector to sector sniffing out information on the disk. When you format a disk you ask the computer to inspect the magnetic surface of the disk for any errors, prepare it for use by future data and create an index "file allocation table (FAT)" which is like a card index for a large library of books. Formatting a disk is a little like taking a blank piece of paper and using a pencil and ruler to turn it into graph paper with both horizontal and vertical lines. What was blank before now has little cells or file drawers which can hold information. The file allocation table is so crucial to keeping track of where the data is on the disk that DOS (the disk operating system) usually keeps two copies in case of errors. Without a file allocation table the disk is like a large public library with no card catalog index and (worse still) every light in the building has been turned off! Certain utilities contained in DOS (i.e., the debug utility) and other software programs can adjust or repair the file allocation table but generally this is a delicate operation a beginner should not attempt. Floppy disks are available in two types: single and double sided. This means that the manufacturer guarantees only one (or both) sides of the disk as capable of holding magnetic pulses. Usually both sides of all disks are chemically coated, but the manufacturer may have found defects and advises use of only one side. IBM compatible machines usually use double sided, double density disks (abbreviated as DSDD on the package.) Single density disks record magnetic pulses or computer bits at 2,768 bits per inch and double density at 5,876 bits per inch. A single sided disk may work in a machine for a while, but you DO stand a risk that the data may be lost in time on the second "non-certified" side of a single sided disk. Do NOT turn over a disk and attempt to use the other side! Two problems arise: the disk spins in the opposite direction which may cause data errors and the small write protect notch is in the wrong location which may damage the floppy drive mechanism. What is the difference between a bit and a byte? The IBM PC and its clones generally use 8 bits (electrical pulses) to make up a byte (computer word.) A ninth "odd bit" is used for error checking (parity testing) to make sure the other eight bits are not accidentally erased or lost during storage or use by the computer. Bits are like alphabet characters and bytes are like the words made up from alphabet characters. So how many bytes are stored on a floppy disk? 40 tracks per side x 2 sides per disk x 9 sectors per track x 512 bytes per sector = 368,640 bytes stored per disk assuming DOS version 2.0 or later. Basically this means about one third of a million pieces of data information - quite a bit! On the side of all floppy disks is a small square notch. If the notch is uncovered, data can be freely written to the disk. If covered with tape, the PC will NOT write to the disk but CAN read from the disk. This is called the write protect tab. Be careful when handling disks! Since the read/write magnetic head on a floppy rides delicately in contact with the disk, tiny obstructions can cause it to jump, skip or scratch the disk and lose your data. Fingerprints, smoke, hair and moisture can cause problems. Always handle a floppy disk by the edges of its protective plastic "jacket" and replace it in a paper or plastic Tyvek slipcover sleeve when not in use. In addition, magnets, x- rays, televisions and other sources of stray magnetism can cause a floppy disk to lose data. Hard disks have many of the same characteristics as floppy disks, but are managed and maintained in a different manner as we will see in a later expanded tutorial on hard disks within package. In brief, however, hard disks use aluminum or hardened glass platters rather than flexible plastic mylar. Usually several platters are stacked together within a single hard drive unit. The number of stacked platters determine the data capacity of the hard drive unit. Because the hard disk platter spins much faster and holds data packed more tightly that a floppy disk, the hard drive unit is usually sealed in a metal shroud or container to eliminate dust or other contaminants. A sealed hard drive is sometimes referred to as a Winchester disk or Fixed drive. Where a floppy disk might hold approximately 360,000 bytes (abbreviated as 360K), a hard drive holds 10 Megabytes (million bytes) or more. As we will discuss later, backing up (making spare copies of hard drive data onto floppy or tape) is a necessary task since hard drives can and do fail - taking precious data with them. The bottom line is that once you get started with a computer, quite quickly your data becomes far more valuable than the computer in which it resides! Since we have briefly covered data storage we need to talk about data input. Two primary input devices are central to getting data into a pc. The keyboard and the mouse. We will discuss the keyboard in greater detail in a later tutorial. The mouse is an alternate input device which is rolled or moved across the desktop to position a cursor or pointer on the computer screen. The mouse also contains several buttons to help select items on data on the monitor screen. A mouse is not necessary for computer input - it is an optional device. Another introductory topic is that of output devices such as a monitor, printer or plotter. A plotter is a device which uses a motor to move pens or drawing implements in tightly controlled horizontal and vertical motions on a piece of paper or film. The computer can control a plotter to combine on one piece of paper differing pen colors and text and pictures stored within the computer. Computer plotter can be purchased with flat table or flat bed configurations or in models which move the pen(s) back and forth with gears that also drive the paper movement at the same time. The printer is probably the most common and useful output device attached to your computer. There are many types of modern computer printer with differing speeds and capabilities. The most common printer is the dot matrix printer which provides characters made up from tiny dots of ink on paper. The Daisy wheel printer uses a rapidly spinning wheel to imprint each letter separately like any ordinary typewriter. Line printers print entire lines of text in one sweep then move to the next line and are thus very fast. Ink jet printers produce characters made from individual dots of ink sprayed onto the paper. Thermal printers contain tiny wires which burn and thus darken special thermal paper into tiny letters and dots which we can read. Finally laser printers use a rapidly scanning laser to sensitize a polished drum with an entire page of information quickly and look and work roughly like an office copier. The first three types of printer are classified as impact printers since something strikes the paper which the later three are non impact printers. The oldest printer design is the thermal printer which maintained some popularity and was easy to manufacture, however the use of thermal printers is fading since the special heat sensitive paper is expensive and subject to random extraneous marks and blurring. The laser and ink jet printers are becoming more popular due to rapid speed of printing and quiet mode of operation. They are expensive with prices ranging from $600 to $2000. The ink jet printer squirts individual dots of ink onto the paper to form letters or other characters. A high quality paper is necessary since the wet ink can smear if not carefully handled. The laser printer is used for quickly producing one page of text at a time. In operation, the laser scans a polished drum with an image which is then dusted with dark toner particles which stick to the exposed areas made sensitive by the laser. Paper is then placed in contact with the drum and the toner is transferred to the page and is finally fused with heat to "fix" or seal the toner particles to the page. Dot matrix and daisy wheel printers are common and affordable alternatives for many small offices and home computer hobbyists. The two differ in the sharpness and quality of the final printed document. Dot matrix printers produce letters via small pins which strike the ink ribbon and paper to produce print which can be jagged looking. Nine pin dot matrix printers produce somewhat rough looking letters while 24 pin dot matrix printers produce crisper, fully-formed letters. In many cases the 24 pin dot matrix printer approaches the quality of the daisy wheel printer which seems to be fading from the computer printer scene. Both dot matrix and daisy wheel printers strike the paper through a ribbon to transfer ink to the printed page. Connecting a printer via a cable to the computer is always done through one of two plugs (or interfaces) on the back of the computer. One type of interface (computer plug) is serial, the other called parallel. The most commonly used interface for printers today is the parallel interface but serial interface printers do exist. What is the difference? Recall that there are eight bits (computer dots and dashes) to a byte (or computer word). The serial interface has each bit sent one at a time to the printer - like men in single file at the supermarket checkstand. The parallel interface sends all eight bits at once - like eight men all entering eight supermarket checkstands at once. Each interface is different, the printer manufacturer will tell you which interface to use. As a clue, frequently modems or mouse devices use the serial interface leaving the printer to the parallel interface. We have talked about output to paper, next let's briefly discuss output to a monitor or screen. The monitor or video display works much like your television - some older home computers still use a TV. Another term for a monitor is the cathode ray tube or CRT. Monitors differ in the sharpness or resolution they can display. On the low end of the resolution spectrum is the monochrome (single color) monitor frequently available in either green or amber screens. Next is the color RGB monitor (RGB stands for Red, Green and Blue) which displays low resolution color dots to make up an image. Higher resolution is obtained with an EGA monitor (Enhanced Graphics Adapter) and still higher with a VGA (Video Graphics Array) Monitor. Each monitor is mated to work with a circuit card located within the body of the computer. One way to upgrade a computer is to switch both the monitor and display/graphics circuit card to produce a sharper, more colorful image. The dots which make up all images on the monitor screen are called pixels. The smaller the pixels, the higher and sharper the image resolution. What is the difference between computer hardware and software? In simplest terms, hardware is the physical parts associated with a computer - the circuit boards, floppy drives, printers, cables and physical pieces of a system. Software is the electronic instructions necessary to make the computer perform. These instructions are usually stored inside a piece of hardware (e.g., software instructions stored inside a circuit chip or floppy drive) but they are nevertheless software. There are two major types of software: operating system software and applications software. Operating system software (like DOS) performs very elemental housekeeping instructions (e.g., where is monitor, how can I keep track of what data is on which track or sector of a floppy drive.) Applications programs perform tasks on a higher level (e.g., word processing programs or database programs are applications.) Generally an application software package uses the lower level operating system (DOS) to do routine tasks (e.g., your word processing application uses the lower level DOS operating system frequently to write and store data on a disk. We interrupt this tutorial for a brief reminder: be sure to submit your registration fee to receive your BONUS DISKS! Now back to our regularly scheduled tutorial . . . ---------------------------------------------------------------- INTRODUCTION TO COMPUTER TECHNOLOGY - PROCESSING AND THE CPU ---------------------------------------------------------------- You can pause for a while if you like or go onto to another tutorial. But if you want delve into great complexity, read on. Now it's time to delve deeper into the heart of the computer. The central processing unit or CPU is the "brains" of every computer. On the PC, the CPU is simply a tiny integrated circuit. It is the control center and contains two circuit elements to perform tasks plus several special locations or memory areas called registers which hold instructions. Registers, located within the CPU chip are temporary storage locations which hold instructions. Secondly, the arithmetic logic unit or ALU is the location within the CPU where seven basic math and logic operations take place (such as addition and subtraction.) Finally, the control unit is a portion of the CPU which directs all elements of the computer. It does not add or subtract like the ALU, it only directs the activity. Let's first examine the registers within the CPU. Four registers are present in the CPU - some computers contain more than four. The storage register is simply a parking area for information taken from or sent to memory. The accumulator register accumulate the results of calculations. The address register stores the location of where the information or instructions are located. Finally, one or more general purpose registers are usually available and have several functions which can interchangeably include addressing (where is it?) or arithmetic (add or subtract it.) Registers can vary in size or bits with the variety of the computer. 8-bit registers are common on small computers. 16-bits for larger personal computers. And finally minis, mainframes and supercomputers have 64-bit or larger registers. This length (8- bit, 16-bit, etc) is called a word and frequently larger and more powerful computers feature larger register size. Despite this seeming complexity a basic fact remains: all digital computers can only add and subtract two numbers: zero and one! Let's back up a bit. For purposes of digital computer electronics, internally a computer can only respond to two things: on and off - just like a light switch. These electronic states of being might actually be a positive and negative voltage or a high and low voltage stored in a series of transistors etched in silicon on a chip, but to the computer the logic is on or off. Two conditions, that is all. Back in the human world we can represent these as one and zero (1 and 0). A special branch of mathematics deals with calculations of numbers represented by 1 and 0 which is called binary arithmetic. Each one or zero is a pulse of electricity or magnetism (electricity inside a chip, magnetism out on the surface of a floppy disk.) Each pulse, either a 1 or 0 is called a bit. Whole series of bits in a row can be used to represent numbers larger than 9 in our human decimal system. Bits in strings of eight units are called bytes. One byte represents a single character of data in the computer. As a curious aside, a nibble is half a byte or four bits. We go back to our analogy of the light switch (on and off representing one and zero to a computer.) In simplest terms, if we have two light switches we have the following ideas: OFF OFF = 0 0 = (human decimal number) zero = 0 OFF ON = 0 1 = (human decimal number) one = 1 ON OFF = 1 0 = (human decimal number) two = 2 ON ON = 1 1 = (human decimal number) three = 3 Notice something peculiar: in the above we find FOUR binary numbers (0,1,2,3) but THREE human decimal numbers (1,2,3.) We rarely think of 0 as a number since we consider it NOTHING.) To computers ZERO is always a number!!! Going a little further a single bit can only represent two numbers: (ON or OFF = 1 or 0 ). Two bits (our above example can represent four numbers (0,1,2,3). And four bits could represent 16 numbers. If you go all the way to a byte (eight bits) you could get 256 numbers. The pattern is that each additional bit doubles the quantity of possible numbers. To a computer these binary numbers march together in a long string, one after another. Remember, the CPU has only two numbers to work with: 1 and 0. Human Computer Decimals Binary 0 - 0 1 - 1 2 - 10 3 - 11 4 - 100 5 - 101 6 - 110 7 - 111 8 - 1000 9 - 1001 10 - 1010 11 - 1011 12 - 1100 13 - 1101 14 - 1110 15 - 1111 Notice several eccentricities about this system. In binary, start on the right and keep adding digits to the left. When you fill a space with all 1's, you zero out everything, add one digit to the left, and start with "1" again. When you reach binary 111 you start the WHOLE series over again with a 1 in front of it. One bit counts two numbers, two bits count four, three bits count eight and so on as we mentioned earlier. When you add a binary digit to the growing string of 1's and 0's you double the number of total decimal digits you can use! These eccentricities appear odd, but to the computer they are shortcuts which simplify calculations and keep things to 1's and 0's. It is this simple system of on and off (like light switches) which make computers and their odd binary system so FAST! Now that we understand the basic binary arithmetic of a computer we can say a few words about addressing. Simply put, each piece of information in the computer lives in a little memory location (like eggs in a carton -each egg is a piece of data, each carton hole is an address or location.) Each address is unique, of course. The first address, the second, and so on. How many addresses can an 8-bit binary number describe? 256. A 16-bit number can specify 65536 addresses or possible locations for data. As we finish our introduction to computer technology we should briefly list a few terms. There are more in the glossary contained elsewhere on this disk. Kilo - Thousand units. Example: kilobyte. Because of the binary math associated, this is actually 1024 bytes. Frequently abbreviated as the simple letter "K". Meg - Million. Example: 20 Meg hard disk which hold 20 million bytes approximately. Millisecond - One thousandth of a second. Microsecond - One millionth of a second. Nanosecond - One billionth of a second. Picosecond - One trillionth of a second. Tutorial finished. Be sure to order your FOUR BONUS DISKS which expand this software package with vital tools, updates and additional tutorial material for laptop users! Send $20.00 to Seattle Scientific Photography, Department LAP, PO Box 1506, Mercer Island, WA 98040. Bonus disks shipped promptly! Some portions of this software package use sections from the larger PC-Learn tutorial system which you will also receive with your order. Modifications, custom program versions, site and LAN licenses of this package for business or corporate use are possible, contact the author. This software is shareware - an honor system which means TRY BEFORE YOU BUY. Press escape key to return to menu.