500 MB Nyheder Direkte fra Internet 2

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Text File | 1994-09-21 | 31KB | 616 lines

KEYBOARDS The usual way to communicate with the computer is to type messages on the computer's keyboard. Famous keyboards These pages show pictures of famous keyboards: Keyboard Page the ideal keyboard324 IBM PC 83-key keyboard422 IBM PC 101-key keyboard422 Mac keyboard 427 Apple 2 keyboard431 Commodore keyboard438 Tandy model 4 keyboard443 Tandy Color keyboard445 IBM PC The IBM PC's keyboard can print all the letters of the alphabet (from A to Z), all the digits (from 0 to 9), and these symbols: SymbolOfficial nameNicknames used by computer enthusiasts . period dot, decimal point, point, full stop , comma cedilla : colon dots, double stop ; semicolon semi ! exclamation pointbang, shriek ? question markques, query, what, huh, wildchar " quotation markquote, double quote, dieresis, rabbit ears ' apostrophesingle quote, acute accent, prime ` grave accentleft single quote, open single quote, open quote, backquote ^ circumflexcaret, hat ~ tilde squiggle, twiddle, not = equals is, gets, takes + plus add - minus dash, hyphen _ underline underscore, under * asterisk star, splat, wildcard, Nathan Hale & ampersand amper, amp, and, pretzel @ at sign at, whorl, strudel $ dollar signdollar, buck, string # number signpound sign, pound, tic-tac-toe % percent signpercent, grapes, James Bond / slash forward slash, rising slash, slant, stroke \ backslash reverse slash, falling slash, backwhack | vertical linevertical bar, bar, pipe, enlarged colon ( )parenthesesopen parenthesis & close parenthesis, left paren & right paren [ ]brackets open bracket & close bracket, square brackets { }braces curly brackets, curly braces, squiggly braces, left tit & right tit <>brockets angle brackets, less than & greater than, from & to, suck & blow For example, the symbol * is officially called an ``asterisk''. More briefly, it's called a ``star''. It's also called a ``splat'', since it looks like a squashed bug. In some programs, an asterisk means ``match anything'', as in a card game where the Joker is a ``wildcard'' that matches any other card. The asterisk is also called a ``Nathan Hale'', since he was the American patriot who during the Revolutionary War declared this final thought before being hanged by the British: ``I regret that I have just one ass to risk for my country.'' The % sign is called a ``James Bond'' because it looks like that spy's code number: 007. The IBM PC's keyboard also contains special keys that help you do special activities, such as move around the screen while you type: Key Usual purpose move up, to the line above move down, to the line below move left, to the previous character ■ move right, to the next character Home move back to the beginning End move ahead to the end Page Up move back to the previous page Page Down move ahead to the next page Tab hop to next field or far to the right Enter finish a command or paragraph Pause pause until you press Enter Print Scrn copy from the screen to paper Shift capitalize a letter Caps Lock capitalize a whole phrase Num Lock use numbers on keyboard's right side Scroll Lock change how text moves up & down Insert insert new character in middle of text Delete delete the current character Backspace delete the previous character Esc escape from a mistake F1 get help from the computer F2, F3, etc. do special activities Ctrl do special activities Alt do special activities Many programs make those keys serve different purposes instead. Be safe: avoid those keys until you read the details in later chapters. GRAPHICS-INPUT DEVICES If you feed the computer a picture (such as a photograph, drawing, or diagram), the computer will analyze the picture and even help you improve it. To feed the computer a picture, you can use three methods. . . . Method 1: point a video camera at what you want to take a picture of, while the video camera is wired to a box called Computer Eyes, which is wired to the computer. Method 2: draw the picture on paper, then put that paper underneath an optical scanner wired to the computer. Method 3: draw the picture by using a pen wired to the computer. The six popular kinds of computerized pens are light pens, touch screens, graphics tablets, mice, trackballs, and joysticks. Light pens A light pen is a computerized pen that you point at the screen of your TV or monitor. To draw, you move the pen across the screen. Light pens are cheap: prices begin at $20. But light pens are less reliable, less convenient, and less popular than other graphics-input devices. Touch screens A touch screen is a special overlay that covers the screen and lets you draw with your finger instead of with a light pen. Graphics tablets A graphics tablet is a computerized board that lies flat on your desk. To draw, you move either a pen or your finger across the board. The cheapest graphics tablet is the Koala pad. Koala makes versions of it for all the popular computers by IBM, Apple, Commodore, and Radio Shack. Fancier tablets for the IBM PC are made by Wacom. Mice A mouse is a computerized box that's about as big as a pack of cigarettes. To draw, you slide the mouse across your desk, as if it were a fat pen. When you slide the typical mouse, a ball in its belly rolls on the table. The computer senses how many times the ball rotated and in what direction. The mouse was invented at Xerox's Palo Alto Research Center (PARC). The first company to provide mice to the general public was Apple, which provided a free mouse with every Lisa and Mac computer. Now every Mac, Commodore Amiga, and Atari ST computer comes with a free mouse ___ and so do many IBM computers and clones. Microsoft Mouse The nicest mouse for the IBM PC is the Microsoft Mouse. Its first version was boring. Then came an improved version, nicknamed ``The Dove Bar'' because it was shaped like a bar of Dove soap. It felt great in your hand; but trying to draw a picture by using that mouse ___ or any mouse ___ was as clumsy as drawing with a bar of soap. The newest version of the Microsoft Mouse is nicknamed ``The Dog's Paw'' because it's shaped like a dog's lower leg: it's long with an asymmetrical bump (paw) at the end. It feels even better than The Dove Bar, unless your hand is too small to wrap around it. Discount dealers sell it for $59. Cheaper mice If you're nearly broke, buy a cheaper brand of mouse. Prices start at just $10. Trackballs A trackball is a box that has a ball sticking out the top of it. To draw, just put your fingers on the ball and rotate it. Most notebook computers have a trackball built into the keyboard. Technologically, a trackball is the same as a typical mouse: each is a box containing a ball. For a trackball, the ball sticks up from the box and you finger it directly; for a mouse, the ball hides underneath and gets rotated when you move the box. The mouse feels more natural (somewhat like gripping a pen) but requires lots of desk space (so you can move the box). The trackball was invented first. The mouse came later. Joysticks A joystick is a box with a stick coming out of its top. To draw, you move the stick in any direction (left, right, forward, back, or diagonally) as if you were the pilot of a small airplane. The most popular joysticks are made by Atari and Kraft. Atari joysticks work just on Atari and Commodore computers. Kraft joysticks are nicer, more expensive, and work on all popular computers by IBM, Apple, Commodore, and Radio Shack. SPEAKERS To produce sounds, the typical computer uses a speaker (similar to the speakers in your stereo system, but smaller). The speaker is typically inside the system unit. Some computers use the speaker in your TV or monitor instead. By using the speaker, the computer beeps at you whenever you make an error. Aesthetic computers, such as the Mac, can make the speaker play nice music. The IBM PC is a boring business computer that produces just harsh beeps, unless you make the IBM PC sound as good as a Mac by inserting a sound card (such as the Sound Blaster). The fanciest computers can speak words, by attaching the speaker to a speech synthesizer. The newest Mac computers come with a microphone. (You can also add a microphone to other computers.) By using the microphone, you can make the computer record sounds. For example, you can make the computer record the sound of your voice and imitate it, so the computer sounds just like you! MODEMS You can connect your computer to a telephone line so your computer can chat with other computers around the world! Here's how. . . . To let your computer chat with a computer that's far away, attach each computer to telephone lines by using a ``special device'' that turns computer signals into telephone signals, and turns telephone signals back into computer signals. Turning a computer signal into a telephone signal is called modulating the signal. Turning a telephone signal back into a computer signal is called demodulating the signal. Since the ``special device'' can modulate and also demodulate signals, the device is called a modulator/demodulator (or modem, which is pronounced ``mode em''). Acoustic versus direct-connect You can buy two kinds of modems. The old-fashioned kind is a black box that has big ears on top, so that it can listen to the telephone. Because of its big ears, it's called a Mickey Mouse modem or an acoustic coupler. It usually costs $120. The newer kind of modem plugs directly into the phone system, as if it were an answering machine. It doesn't have any ears: it has telephone wires instead. It's called a direct-connect modem. It usually costs under $100, and it's cheaper and more reliable than a Mickey Mouse modem. It's more popular than a Mickey Mouse modem because it's better than a Mickey Mouse modem in every way, except that you can't attach it to pay phones or to phones in hotel rooms. Kinds of direct-connect modems A direct-connect modem can be either external or internal. If it's external, it's a box that sits next to your computer. If it's internal, it's a printed-circuit card that hides inside your computer. Regardless of whether it's external or internal, a wire runs from it to the phone system. Internal modems are more popular than external ones, because external modems typically cost more and require that you buy a cable to run from the modem to the computer. But external modems have the advantage of being easier to control, since they give you push-buttons and blinking lights. Many notebook computers include internal modems at no extra charge. So do some desktop computers. Most direct-connect modems have fancy features, such as auto-dial (which means the modem can memorize the other computer's phone number and dial it for you) and auto-answer (which means the modem automatically answers the phone whenever the other computer calls). A direct-connect modem having many such fancy features is called smart. Nearly all modems sold today are smart. 10 bits per character To transmit a character, the modem usually transmits a 10-bit number, like this: 1001011101. The first bit (which is always a 1) is called the start bit; it means ``hey, wake up, and get ready to receive the data I'm going to send you''. The last bit (which is always a 1) is called the stop bit; it means ``hey, I'm done, you can go back to sleep until I send you more data''. The eight middle bits (such as 00101110) are usually called the data bits: they're a code that represents 1 byte of information (1 character). So to transmit 1 character, the modem transmits 10 bits. Speed The typical modem transmits 2400 bits per second (2400 bps). That speed is also called 2400 baud. Since 10 bits make a character, that kind of modem transmits 240 characters per second. That speed is quite fast: it's about as fast as the average person can read. Faster modems can transmit 9600 bits per second (which is 9600 bps, 9600 baud, 960 characters per second). That's faster than you can read, but it's great for transmitting documents that you want to skim, programs that you want to run, and graphics. Even faster modems can transmit 14400 bits per second. Since 1000 bits is called a kilobit, 14400 bits per second is called 14.4 kilobits per second (or 14.4 kbps or 14.4 kilobaud). Some computerists still use old modems transmitting just 1200 bits per second (1200 baud) or 300 bits per second. If you buy a fast modem, you can tell it to go slower. For example, if you buy a 9600-baud modem, you can tell it to go at five popular speeds: fast (9600 baud), medium (2400 baud), slow (1200 baud), and super-slow (300 baud). To communicate with a friend's computer, your modem must go at the same speed as your friend's. For example, if you buy a 9600 baud modem but your friend has just a 300-baud modem, your modem's software will detect the slowness of your friend's modem and automatically downshift (slow down) to 300 baud. Standards Standards for modem communication have been invented by AT&T and a French-speaking international committee called the Comité Consultatif International Télégraphique et Téléphonique (CCITT). Here's what they call their standards: SpeedCCITT standardAT&T standard 300 bpsV.21 Bell 103 1200 bpsV.22 Bell 212a 2400 bpsV.22bis 9600 bpsV.32 14400 bpsV.32bis 19200 bpsV.32terbo 28800 bpsV.34 (or V.fast) For example, if you see an ad for a V.22-compatible modem or a Bell 212a modem, the ad is trying to sell you a 1200 bps modem. Notice that the second version of V.22 is called V.22bis, because bis is a French word that means ``2nd version''. Notice that the third version of V.32 is called V.32terbo, because terbo is an international word that combines the French ``ter'' (which means 3) with the English word ``turbo'' (which means ``fast''). Find all those terms confusing? That's why computerists say that ``CCITT'' really stands for ``Committee for Confusing International Telecommunications Terms''. Data compression Modems sometimes use a shorthand notation that lets data to be expressed in fewer bits than normal, so more data can be transmitted per second. The shorthand notation is called a data-compression technique. The most popular data-compression techniques are Microcom's MNP level 5 (which compresses data to half as many bits as normal), Microcom's MNP level 7 (which compresses data to a third as many bits as normal), and CCITT's V.42bis (which compresses data to a fourth as many bits as normal). For example, if you see an ad for a 2400-baud modem with MNP level 5, that modem will transmit about as much data per second as a plain 4800-baud modem. Fax You can send messages from your computer to fax machines around the world, if you buy a fax/modem, which is a modem that can also send faxes. If the fax/modem is fancy, it can also receive faxes and print them on your printer. The typical fax/modem transmits modem information (to other computers) at 2400 baud. It transmits faxes (to fax machines) at 9600 baud. It's called a 2400/9600-baud fax/modem. (Most ads list the modem speed first, then the fax speed, because the modem speed is more important.) More briefly, it's called a 2496 fax/modem. Warning: though every 2496 fax/modem can send faxes at 9600 baud, the cheapest 2496 fax/modems receive faxes at just 4800 baud ___ or can't receive faxes at all! Faster fax/modems can transmit 14400 baud (14.4 kilobaud) for faxes and modem data. Brands The most famous modems are made by Hayes, which charges high prices. Other companies make cheaper modems that imitate Hayes' and are called Hayes-compatible. Nearly all modems sold today are Hayes-compatible. For example, high-quality Hayes-compatible modems have been built by Everex and Practical Peripherals. To avoid competition from those companies, Hayes sued Everex and bought Practical Peripherals. So Everex had to pay Hayes a royalty (and eventually stopped selling modems), and Practical Peripherals become owned by Hayes. To pay less for a Hayes-compatible modem, get the ones made by Zoom. You can get another brand, Infotel, at even lower prices. For example, you can get a 14400-baud Infotel fax/modem for just $85 internal, $99 external, from a discount dealers such as Midwest Micro (in Ohio at 800-972-8822). If even $85 is beyond your budget, spend just $40, which gets you an internal fax/modem handling modem data at 2400 baud, sending faxes at 9600 baud, and receiving faxes at 4800 baud. That's the price for the cheapest Best Data modem at Staples (a chain of office-supply stores); it's also the price for the cheapest Boca Research modem at USA Flex (an Illinois discount dealer at 800-944-5599 or 708-582-6206). COM1 versus COM2 A modem is an example of a serial device. You might own another serial device also, such as a serial mouse or a serial printer. The IBM PC can handle two serial devices simultaneously. The first serial device is called communication device #1 (COM1). The second serial device is called COM2. If you add a modem to your IBM PC or clone, you must decide whether to call the modem COM1 or COM2. Most hardware and software assume the modem is COM2. To avoid headaches, make the modem be COM2. Here's how. If the modem is external, run its cable to your computer's COM2 port. (If your computer doesn't have a COM2 port yet, buy a serial interface card containing it.) If the modem is internal, make sure the switch or jumper on the modem is set to the COM2 position; and make sure no other hardware in your computer system is called COM2. For example, if your computer contains a serial interface card having a COM2 port on it, you must disable the serial interface card's COM2 port (by moving a jumper or switch on it). Avoid using COM3 or COM4, since the computer has trouble handling COM3 and COM4 reliably. (COM3 often conflicts with COM1, and COM4 often conflicts with COM2.) TAPES Like a disk, a magnetic tape consists of magnetized rust. Just as you put a disk into a disk drive, you put a tape into a tape drive. Tape drives are slower than disk drives. To skip from the disk's beginning to the disk's end, the disk drive's arm simply hops from the outermost track to the innermost track. But to skip from the beginning of a tape to the end of a tape, you must wait for the tape drive to wind the entire tape. Cassettes for primitive computers The cheapest kind of tape drive is an audio cassette tape recorder ___ the same kind you use for listening to music, at the beach or in your car. You can attach that kind of tape recorder to an old Radio Shack computer (such as the Radio Shack TRS-80 model 1, 3, or 4 or the Radio Shack Color Computer). Wires run from the tape recorder to the computer, and the computer sings a song into the tape recorder; the song is a code that represents the data. Unfortunately, audio cassette tape recorders aren't very reliable. If you're using one of those old Radio Shack computers, you can improve the reliability somewhat by getting Radio Shack's own tape recorder, which is specially designed to work well with computers and automatically controls the tape's volume. But since a tape recorder is so much slower than a disk drive, I recommend that you not buy Radio Shack's tape recorder, and instead keep saving your pennies until someday you can afford a disk drive. Once you've experienced the thrilling speed, convenience, and pleasure of a disk drive, you'll never want to use a tape recorder ever again! Commodore & Atari Old computers by Commodore and Atari (such as the Commodore Vic, Commodore 64, Commodore 128, and Atari 800) do not attach to ordinary audio cassette tape recorders; you must buy special cassette tape recorders sold by Commodore and Atari or ___ better yet ___ buy a disk drive instead, if you can afford it. Coleco The Coleco Adam computer comes with a built-in cassette tape recorder, at no extra charge. Coleco's tape recorder is high-speed and requires specially lubricated tapes, sold by Coleco. Since it handles just tapes that contain computer information and cannot play ordinary musical tapes, it's called a digital cassette tape drive instead of an audio cassette recorder. But even though Coleco's tape recorder is ``high-speed'' and handles computer data rather well, it's still not nearly as fast or convenient as a disk drive. Modern microcomputers Most people who buy modern computers (such as the Mac, Commodore Amiga, IBM PC, and clones) buy disk drives and don't bother using tapes at all. If you buy a hard disk, how do you make a backup copy of that hard disk, and where do you put the backup? You could put the backup copy onto a second hard disk or onto a pile of about 50 floppy disks. Another possibility is to put the backup copy onto a special super-fast digital cassette tape drive that holds super-long cassette tapes that can contain backups. Colorado The most popular such tape drives are the Jumbo 120 and the Jumbo 250, both built by Colorado Memory Systems (which used to be an independent company but is now owned by Hewlett-Packard). Those Jumbo drives work with the IBM PC and clones. The Jumbo 120 can back up a 120-megabyte hard disk by taking the hard disk's data, compressing it into a shorthand notation, and then storing the compressed data on a 60-megabyte tape. Because of that scheme, the Jumbo 120 is called a 60/120M tape drive. The Jumbo 250 can back up a 250-megabyte hard disk by compressing the hard disk's data onto a 120-megabyte tape. It's called a 120/250M tape drive. The Jumbo 120 uses the same blank tape as the Jumbo 250. The Jumbo 120 formats that tape to hold 60 megabytes of data (from a 120-megabyte drive), whereas the Jumbo 250 takes the same tape but formats it differently, to hold 120 megabytes of data (from a 250-megabyte drive). To buy those drives cheaply, phone discount dealers such as USA Flex (800-USA-FLEX) and Insight (800-755-3874). Here's what they'll charge you: Item Price Jumbo 120 drive $99 Jumbo 250 drive $165 tape, unformatted $15 each (if you buy 5) tape, formatted for Jumbo 250 $16 each (if you buy 5) Each Jumbo drive is internal: it goes inside your computer. It uses the same controller card that controls your floppy disk drives. If you want to put the drive outside the computer, put the drive in an external case that costs $80. Alternatives Instead of buying a tape drive, the typical computerist uses a pile of floppy disks or buys a second hard drive. Big reels for big computers Maxicomputers and minicomputers use big reels of tape for three purposes: to backup big disks, to send data by mail, and to store the archives (old files that are used rarely if ever). The reel's diameter is 10½ inches. If you unwind the tape, you'll find the tape is half an inch wide and almost half a mile long! The exact length is 2400 feet. To use a reel of tape, you put the reel into a reel-to-reel tape drive, which typically costs about $5000 and writes 1600 bytes per inch, so that the entire tape holds 43 megabytes. Super-fancy drives, used only on the largest maxicomputers, squeeze 6250 bytes onto every inch (instead of 1600), so that they squeeze 171 megabytes onto a single reel of tape. IBM's fanciest drive not only writes 6250 bytes per inch but also does the writing amazingly quickly. It moves the tape at 200 inches per second, so that it transfers about 1.2 megabytes per second. CASES The motherboard and other main circuitry are enclosed in a box. The box and the circuitry inside it are called the system unit. The box itself ___ without its contents ___ is called the case. Interference The computer thinks at about the same speed (number of cycles per second) as radio & TV waves. If you put your computer next to a radio or TV, the computer's electromagnetic ``thought waves'' cause static on the radio or TV. To decrease that interference, move the computer away from the radio or TV (or change the position of the radio or TV's antenna). The Federal Communications Commission (FCC) prohibits you from owning any device (such as a computer) that interferes with your neighbors' radio and TV. The FCC requires all computers to pass the FCC class A non-interference test. Any computer used in a residential area must also pass the FCC class B non-interference test, which is harder to pass than the class A test. To help the computer pass the class A and class B tests, manufacturers line the insides of cases with metal that breaks up the electromagnetic waves. When you buy a computer, ask whether it's FCC class B approved. If it's not ___ if it's just FCC class A approved ___ you cannot legally use it in a residential area. SURGE SUPPRESSORS Instead of plugging your computer into the wall, you can plug it into a surge suppressor, which is a special extension cord that protects your computer against surges in electrical power. Unless you live in a neighborhood or building that has extremely poor electricity, don't bother buying a surge suppressor. The typical computer has some surge protection built into it already. If you're worried about thunderstorms sending surges to your computer, just unplug your computer during storms! If your air conditioner or electric heater consumes too much electricity and causes a brownout (so your computer acts unreliably), use a plain extension cord to plug your computer into a different outlet, so that the computer's not on the same circuit as the power-hungry appliance. During the summer, most computer errors are caused by temperatures over 95°, not by power surges.