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CHIP TECHNOLOGY The system unit is the box containing the CPU and other goodies (such as the speaker, power supply, and memory). If you unscrew that box and pry it open to see the circuitry inside, you'll see a green plastic board, on which is printed an electrical wiring diagram. Since the diagram's printed in copper (instead of ink), the diagram conducts electricity; so it isn't just a diagram of an electrical circuit; it is an electrical circuit! The green plastic board ___ including the circuit printed on it ___ is called a printed-circuit board (PC board). Each wire that's stamped onto the PC board is called a trace. The typical computer contains several PC boards. Motherboard & babies In your computer, the largest and most important PC board is called the motherboard. It lies flat on the bottom of the system unit. The other PC boards are smaller. Those little baby boards (about the size of a postcard) are called PC cards. The typical motherboard has several slots on it. Into each slot, you can put a PC card. PCMCIA cards If you buy a modern notebook computer, you'll see the case's right-hand wall has a special slot in it. You can shove a card into that slot without opening the notebook's case. The kind of card that fits into that special slot is small and thin ___ the size of a credit card. That kind of card was invented by the Personal-Computer Memory-Card International Assocation (PCMCIA) and therefore called a PCMCIA card. That slot is called a PCMCIA slot. People have trouble remembering what ``PCMCIA'' stands for. Cynics say it stands for ``People Can't Memorize Computer Industry Acronyms''. Since ``PCMCIA'' also stands for ``Politically Correct Members of the CIA'', computerists pronounce ``PCMCIA'' in two breaths: they say ``PCM'', then pause, then say ``CIA''. Some PCMCIA cards are very thin. Other PCMCIA cards are slightly thicker, so they can hold extra circuitry. A PCMCIA card and its slot are called Type 1 if their thickness is 3.3 millimeters, Type 2 if 5 millimeters, Type 3 if 10.5 millimeters, Type 4 if 18 millimeters. Caterpillars On each PC board, you'll see black rectangles. If you look closely at a black rectangle, you'll see it has tiny legs, so it looks like a black caterpillar. (Though farmers think it looks like a ``black caterpillar'', city folks think it looks more like a ``yucky roach''. Kids call it just ``a black thingy with legs''.) The ``caterpillars'' come in many sizes. In a typical computer, the shortest caterpillars are three-quarters of an inch long and have 7 pairs of legs; the longest are two inches long and have 20 pairs of legs. Though each black caterpillar has legs, it doesn't move. It's permanently mounted on the PC board. Each leg is made of tin and called a pin. Sadistic hobbyists play a game where they yank the caterpillars from a PC board and throw the caterpillars across the room. That game's called ``tin-pin bowling''. Hidden inside the caterpillar is a metal square, called a chip, which is very tiny. The typical chip is just an eighth of an inch long, an eighth of an inch wide, and a hundredth of an inch thick! On that tiny metal chip are etched thousands of microscopic electronic circuits! Since all those circuits are on the chip, the chip's called an integrated circuit (IC). Four purposes Each chip serves a purpose. If the chip's purpose is to ``think'', it's called a processor chip. If the chip's purpose is to ``remember'' information, it's called a memory chip. If the chip's purpose is to help devices communicate with each other, it's called an interface chip. If the chip's purpose is to act as a slave and helper to other chips, it's called a support chip. So a chip is either a processor chip or a memory chip or an interface chip or a support chip ___ or it's a combination chip that accomplishes several purposes. How chips are designed To design a chip, the manufacturer hires an artist, who draws on paper a big sketch of what circuits are to be put onto the chip. It helps if the artist also has a degree in engineering ___ and knows how to use another computer to help draw all the lines. After the big sketch is drawn, it is photographed. Have you ever photographed your friend and asked the photography store for an ``enlargement''? To produce a chip, the chip's manufacturer does the opposite: it photographs the sketch but produces a ``reduction'' to just an eighth of an inch on each side! Whereas a photo of your friend is made on treated paper, the tiny photo of the chip's circuitry consists of metal and semiconductors on treated silicon so the photo's an actual working circuit! That photographic process is called photolithography (or photolith). Many copies of that photo are made on a large silicon wafer. Then a cookie cutter slices the wafer into hundreds of chips. Each chip is put into its own caterpillar. The caterpillar's purpose is just to hide and protect the chip inside it; the caterpillar's just a strange-looking package containing the chip. Since the caterpillar's a package that has two rows of legs, it's called a dual in-line package (DIP). That DIP's only purpose is to house the chip. Computer hobbyists are always talking about chips & DIPs. That's why computer hobbyists, at parties, serve chips & dips. And that's why computer hobbyists are called ``dipchips''. Buying chips If you ask a computer dealer to sell you a chip, the dealer also gives you the chip's DIP (the entire caterpillar). Since you've asked for a chip but also received a DIP, you might get confused and think that the caterpillar (the DIP) is the chip. But that caterpillar's not the chip; the chip hides inside the caterpillar. The typical caterpillar-and-chip costs $3. You might pay somewhat more or somewhat less, depending on how fancy the chip's circuitry is. If the circuits in a chip are defective, it's called a ``buffalo chip''. Folks who dislike that tacky term say ``potato chip'' or ``chocolate chip'' instead, like this: ``Hey, the computer's not working! It must be made of chocolate chips!'' You can get chips from these famous mail-order chip suppliers: Chip supplierAddress Phone Jameco 1355 Shoreway Rd., Belmont CA 94002415-592-8097, 24 hours JDR Microdevices2233 Samaritan Dr., San Jose CA 95124800-538-5000 or 408-559-1200 ACP 1310 E. Edinger, Santa Ana CA 92705800-FONE-ACP The following chip suppliers are newer and often charge less: Chip supplierAddress Phone Nevada Computer684 Wells Rd., Boulder City NV 89005800-982-2928 or 702-294-0204 LA Trade 22825 Lockness Ave., Torrance CA 90501800-433-3726 or 310-539-0019 Pacific Coast Micro4901 Morena Blvd. #1111, San Diego CA 92117800-581-6040 or 619-581-1439 Wordwide Tech21 South 5th St., Philadelphia PA 19106800-457-6937 or 215-922-0050 Memory Express15140 Valley Blvd., City of Industry CA 91744800-877-8188 or 818-333-6389 Chip Merchant9541 Ridgehaven Ct., San Diego CA 92123800-426-6375 or 619-268-4774 How chips chat The chip inside the caterpillar acts as the caterpillar's brain. The caterpillar also contains a ``nervous system'', made of thin wires that run from the brain (the chip) to the legs (the pins). The wires in the caterpillar's nervous system are very thin: each wire's diameter is about half of a thousandth of an inch. If one caterpillar wants to send electrical signals to another caterpillar, the signals go from the first caterpillar's brain (chip) through the caterpillar's nervous system to its legs (pins). Each pin is attached to a trace (wire) on the PC board. The signals travel through those traces, which carry the signals across the PC board until the signals reach the second caterpillar's pins. Then the signals travel through the second caterpillar's nervous system to that caterpillar's brain (chip). Binary code To communicate with each other, the caterpillars use a secret code. Each code is a series of 1's and 0's. For example, the code for the letter A is 01000001; the code for the letter B is 01000010; the code for the number 5 is 101; the code for the number 6 is 110. That's called the binary code, because each digit in the code has just two possibilities: it's either a 1 or a 0. In the code, each 1 or 0 is called a binary digit. A binary digit is called a bit. So in the computer, each bit is a 1 or a 0. When a caterpillar wants to send a message to another caterpillar, it sends the message in binary code. To send a 1, the caterpillar sends a high voltage through the wires; to send a 0, the caterpillar sends little or no voltage through the wires. So to send the number 5, whose code number is 101, the caterpillar sends a high voltage (1), then a low voltage (0), then a high voltage (1). To send those three bits (1, 0, and then 1), the caterpillar can send them in sequence through the same leg (pin); or for faster transmission, the caterpillar can send them through three pins simultaneously: the first pin sends 1, while the next pin sends 0 and the third pin sends 1. The speed at which bits are sent is measured in bits per second (bps). Bipolar versus MOS Chips can be manufactured in two ways. The old way's called bipolar. The new way's called metal-oxide semiconductor (MOS, which is pronounced ``moss''). The new way (MOS) is more popular because it costs less, consumes less electricity, and can hold more circuitry inside the chip. Microcomputers use only MOS. Minicomputers and maxicomputers use mainly MOS chips but also contain a few bipolar chips, because bipolar chips have one (and only one) advantage over MOS chips: bipolar chips work faster. The most popular kind of MOS is called negative-channel MOS. (It's also called n-channel MOS or NMOS, which is pronounced ``en moss''.) The main alternative, called complementary MOS (or CMOS, pronounced ``sea moss''), consumes even less electricity but can't hold as much circuitry inside the chip. CMOS chips are used in simple-minded battery-operated computers (such as digital watches, pocket calculators, pocket computers, and notebook computers) and in some parts of larger computers. CPU The part of the computer that thinks (``the brain'') is called the processor (or central processing unit or CPU). In a maxicomputer or minicomputer, the processor consists of several chips, which are processor chips. In a microcomputer, the processor is so small that it consists of just a single chip, called a microprocessor. It sits on the motherboard. Yes, in a typical microcomputer, the part that does all the thinking is just a tiny square of metal, less than ¼" on each side! Intel's designs In the IBM PC and clones, the microprocessor uses a design invented by Intel. I'll begin by explaining the Intel microprocessors. I'll discuss competitors later. In the original IBM PC (and in the IBM PC XT), the microprocessor was the Intel 8088. IBM computers (and clones) containing that chip are called XT-class computers. Later, Intel invented an improved version, called the Intel 80286. Since ``80286'' is too long a number for us humans to remember, most of us just call it the Intel 286. IBM used it in the IBM PC AT computer. That's why computers containing that chip are called AT-class computers. After inventing the Intel 286, Intel invented a further improvement (called the Intel 386), then an even further improvement (called the Intel 486). In 1993, Intel began selling an even further improvement, which ought to be called a 586; but Intel calls it the Pentium instead, so Intel can trademark the name and prevent companies from copying it. It's the first computer chip that sounds like a breakfast cereal: ``Hey, kids, to put zip into your life, try Penti-yumms. They build strong bodies, 5 ways!'' So altogether, IBM microcomputers and clones come in five popular classes: When Transistors Chip inventedon chip Used in 8088 1979 29,000 XT computers 286 1982 134,000 AT computers 386 1985 275,000 386 computers 486 1989 1,200,000 486 computers Pentium 1993 3,100,000 Pentium comp. You can find programs that run okay on any chip; but many modern programs require a 286, 386, 486, or Pentium and won't run on an 8088. To run modern programs QUICKLY and use all the modern features, you need a 386, 486, or Pentium. Most computers built today contain a 486 or Pentium. The 8088 and 286 chips are found just in pocket computers, used computers, and old computers that liquidators are trying to unload. Many homes and offices still have old 8088 computers, bought many years ago. The people who still use those ancient computers restrict themselves to running very old-fashioned programs. The Intel 386 comes in two varieties. The original variety was called the Intel 386DX. Later, Intel invented a stripped-down version called the Intel 386SX, which saves you money by being much cheaper (and just slightly slower). Similarly, the Intel 486 comes in two varieties: the original variety was called the Intel 486DX; later, Intel invented a stripped-down version called the Intel 486SX, which is much cheaper and just slightly slower. The Intel 8088 is a slightly stripped-down version of a chip called the Intel 8086 (which few computers contain). So altogether, here are Intel's popular chips, from slowest to fastest: slowest & cheapest:Intel 8088 Intel 8086 Intel 286 Intel 386SX Intel 386DX Intel 486SX Intel 486DX fastest & most expensive:Intel Pentium Imitations Intel's competitors have imitated Intel's chips. The most popular imitation of the 8088 is the V20 chip. It's made by Nippon Electric Company (whose abbreviation is NEC, which is pronounced ``neck''). People who use the V20 chip are said to have ``gone necking''. The most popular imitation of the 8086 is NEC's V30 chip; people who use that chip are said to have ``done advanced necking''. Imitations of the 286 are made by Harris. Imitations of the 386 are made by IBM and Advanced Micro Devices (AMD). All those imitations work fine. Some go even faster than Intel's originals! Imitations of the 486 are made by AMD, Cyrix, and IBM. AMD's imitations are fine. Cyrix's imitations are awful: they go much slower that Intel's originals. Cynics say Cyrix's chips should be called ``386½'' instead of ``486''. Cyrix's imitation of the 486SX is called the 486SLC; Cyrix's imitation of the 486DX is called the 486DLC. Like Cyrix, IBM's imitation of the 486SX is called the 486SLC; IBM's imitation runs faster than Cyrix's, though not as fast as Intel's original. Nobody imitates the Pentium yet. Chart of details You've seen that a Pentium is the fastest Intel chip, the 8088 is the worst, and other chips are intermediate. But how much do those chips differ from each other? Don't ask that question to a computer salesman! Computer salesmen dispense lots of misinformation about computers, because the salesmen are lying or stupid. Usually the salesmen are lying and stupid! Here's a famous riddle. . . . What's the difference between a used-car dealer and a computer salesman? Answer: the used-car dealer knows he's lying. To learn the truth about how chips differ from each other, look at this big chart: InternalExternal Math Chip accum.data pathAddresscopr.Megahertz Efficiency 8088 16-bit 8-bit 20-bitno 4.77, 7.18, 8, 10, 12 10% (5%) 8086 16-bit16-bit 20-bitno 8, 10 12% (6%) 286 16-bit16-bit 24-bitno 6, 8, 10, 12, 16, 20 40% (30%) 386SX 32-bit16-bit 24-bitno 16, 20, 25, 33, 40 40% (40%) 386DX 32-bit32-bit 32-bitno 16, 20, 25, 33, 40 50% (50%) 486SX 32-bit32-bit 32-bitno 20, 25, 33 100% (100%) 486DX 32-bit32-bit 32-bityes 25, 33, 40, 50 100% (120%) 486DX2 32-bit32-bit 32-bityes 50, 66 92% (110%) 486DX4 32-bit32-bit 32-bityes 75, 100 90% (108%) Pentium 64-bit64-bit 32-bityes 60, 66, 90 180% (220%) That chart shows the chips we've discussed, listed from worst to best. Some are made by Intel, others by imitators such as Harris and AMD. The chart also shows the Intel 486DX2 and the Intel 486DX4, which are very similar to the Intel 486DX. Here's what the chart means. . . . Internal accumulator Each chip contains registers. Each register can hold a binary code number (such as 01000001). The chip's main register is called the accumulator. If the accumulator is wide enough to hold 32 bits inside it (such as 10000110111001111110010101010101) , the accumulator is called 32-bit; the chip is said to contain a 32-bit accumulator and be 32-bit internally. If the accumulator is narrower and holds just 16 bits, the accumulator is called 16-bit. In that case, the chip can handle code numbers that are 16 bits long but not code numbers that are 32 bits long. If you try to feed that chip a 32-bit code number, the chip won't understand it. The typical program uses just 16-bit instructions. (Instead of using a 32-bit instruction, it uses a pair of 16-bit instructions.) But a few fancy programs use 32-bit instructions. To run those 32-bit programs, you must buy a chip that's 32-bit internally. The chart shows that to run the fanciest programs (32-bit), you must buy at least a 386SX. External data path The column marked ``external data path'' tells how many of the chip's pins transmit data. As you can see from the chart, the 386SX is ``32-bit internal, 16-bit external''. That means the 386SX contains a 32-bit accumulator but has just 16 data pins. To transmit the accumulator's 32 bits, the chip sends out 16 of the bits (on the 16 data pins), then sends out the next 16 bits by using those same pins. That technique of using just a few pins to transmit many bits is called multiplexing. Computerists say the 386SX is ``a 32-bit chip multiplexed onto 16 pins''; they say the 386SX is a multiplexed 386DX. That's why the 386SX is slower than the 386DX: to transmit the 32 bits, the 386SX must send out two bursts of 16 bits, whereas the 386DX can send out a single burst of 32 bits all at once! Notice that the 386SX is just as smart as the 386DX ___ it understands the same 32-bit codes ___ but it transmits them more slowly (as 2 bursts of 16, instead of 1 burst of 32). So the 386SX is smart but a slow communicator ___ like Einstein with his mouth full and trying to talk through a narrow drinking straw. The 8088 is a multiplexed 8086. Like the 8086, the 8088 thinks about 16 bits; but the 8088 must send them out in two 8-bit bursts. Address The computer's main memory (which consists of RAM chips and ROM chips) is like a city: each location in it has an address. If the main memory is large enough to hold lots of info, it has lots of addresses. A city has addresses such as ``231 17th Street, Apartment 501''. In the computer's main memory, each address is a binary code number instead, such as 01000101010111101010. For an 8088 or 8086, each address must be brief: just 20 bits long. An 8088 or 8086 therefore can't handle a big main memory ___ and can't handle big programs. A 286 can handle longer addresses (24-bit) so it can handle the big main memory required by modern big programs. That's why, to run modern big programs, you must buy at least a 286. Though 24-bit addresses are long enough to handle all popular programs sold today, the 386DX permits even bigger addresses (32-bit), to prepare for the bigger programs of the far future ___ and to handle computers that are networked together and share a gigantic big RAM. Math coprocessor You can buy a math coprocessor, which is special circuitry that performs advanced math super-quickly. The math coprocessor's circuits are specially designed to quickly manipulate decimals, trigonometry, logarithms, and 80-bit numbers. If you don't have a math coprocessor, the only way the CPU can do advanced math is by obeying long-winded, slow programs fed to it slowly from the RAM, ROM, and disks. The math coprocessor lets the CPU do advanced math much faster: 10 times faster, 20 times faster, or even more! Should you buy a math coprocessor? If you're doing lots of advanced math, the answer is ``yes'': you'll be amazed and thrilled at how much faster your computer performs the math! But if you're not doing lots of advanced math, don't bother getting a math coprocessor. If you've drawn a picture on the computer's screen and want to rotate the picture, the math coprocessor will make the rotation go faster, because the computer must use trigonometry to rotate the picture and compute the picture's new coordinates. For example, if you draw a 3-D picture of a house and then want the computer to show you how the house looks from a different angle, the math coprocessor will help. Just the 486DX, 486DX2, 486DX4, and Pentium chips contain math coprocessor circuitry; Intel's other CPU chips do not. Here's the difference between a 486DX and a 486SX. . . . A 486DX contains a math coprocessor. A 486SX does not. The 486DX was invented first. Later, Intel invented the 486SX by using this manufacturing technique: Intel took each 486DX whose math coprocessor was faulty and called it a 486SX. So a 486SX was just a defective 486DX. Today, if you buy a 486SX, you're getting a 486DX whose math coprocessor is either defective or total missing. Problem: suppose you want to do advanced math quickly, but your computer's CPU chip lacks math-coprocessor circuitry (because you bought an 8088, 8086, 286, 386, or 486SX). To improve your computer's math speed, just buy a math coprocessor chip, which is a supplementary chip that contains math-coprocessor circuitry. Put that chip next to the CPU chip on the motherboard. Instead of buying a math coprocessor chip made by Intel, you can buy an imitation made by Cyrix or Integrated Information Technology (IIT): CPU Which math coprocessor to buy 8088, 8086 Intel 8087 ($45) 286 Intel 287 ($49) 386SX Intel 387SX ($54), Cyrix 83S87 ($44), or IIT 3C87SX ($52) 386DX Intel 387DX ($74), Cyrix 83D87 ($48), or IIT 3C87 ($54) 486SX Intel 487SX ($299) Megahertz In an army, when solders march, they're kept in step by a drill sergeant who yells out, rhythmically, ``Hup, two, three, four! Hup, two, three, four! Hup, two, three, four!'' Like a soldier, the microprocessor takes the next step in obeying your program only when instructed by the computer's ``drill sergeant'', which is called the computer clock. The clock rhythmically sends out a pulse of electricity; each time the clock sends out a pulse, the microprocessor does one more step in obeying your program. The clock sends out millions of pulses every second, so the microprocessor accomplishes millions of steps in your program every second! Each pulse is called a clock cycle. The clock's speed is measured in cycles per seconds. A ``cycle per second'' is called a hertz (Hz), in honor of the German physicist Heinrich Hertz. A ``million cycles per second'' is called a megahertz (MHz). In the fastest IBM clones, the clock does 66 million cycles per seconds. That's 66 megahertz! In the slowest IBM clones, the clock does just 4.77 million cycles per second. That's 4.77 megahertz. Look at the big chart on the previous page. That chart's bottom line says you can buy three versions of the 486DX chip: the cheapest version can handle 25 megahertz, the standard version can handle 33 megahertz, and the fastest version can handle 50 megahertz. For some chips, the high-megahertz versions are clones manufactured by Intel's competitors instead of by Intel itself. Efficiency and its consequences A 386DX resembles a 486SX: each has a 32-bit internal accumulator, 32-bit external data path, 32-bit address, and no math coprocessor. Which runs your programs faster: a 33-megahertz 386DX or a 33-megahertz 486SX? The answer is: a 33-megahertz 486SX runs your programs twice as fast as a 33-megahertz 386DX, because a 486SX is twice as efficient as a 386DX: it accomplishes twice as much work per clock cycle because it's smart enough to work on several operations simultaneously. In the big chart, the ``Efficiency'' column shows how efficient each microprocessor is, relative to a 486SX. In the ``Efficiency'' column, I give two numbers. The first number shows how efficiently the computer handles simple programs (which contain just 16-bit codes and 20-bit addresses and don't try to use a math coprocessor). The second number (the revised efficiency) is based on the first number but includes a bonus (for having a math coprocessor) and penalties (for being limited to 16-bit instructions or 20-bit addresses). Here's how a 486DX differs from a 486DX2: A 50-megahertz 486DX thinks at 50 megahertz and communicates its answers at 50 megahertz. To use it at full speed, you must put it on a motherboard that has 50-megahertz circuitry. A 50-megahertz 486DX2 thinks at 50 megahertz but communicates its answers at just 25 megahertz. It's intended to be put on a 25-megahertz motherboard (cheaper than a 50-megahertz motherboard). Congratulations! You've learned that a 50-megahertz 486DX2 communicates slower than a 50-megahertz 486DX and therefore has a lower ``efficiency'' rating. Similarly: A 66-megahertz 486DX2 thinks at 66 megahertz but communicates at just 33 megahertz. Put it on a 33-megahertz motherboard. A 75-megahertz 486DX4 thinks at 75 megahertz but communicates at just 25 megahertz. Put it on a 25-megahertz motherboard. A 100-megahertz 486DX4 thinks at 100 megahertz but communicates at about 33 megahertz. Put it on a 33-megahertz motherboard. To compute the total work accomplished, look at the big chart on page 24: multiply the cycle speed (megahertz) by the amount of work accomplished per cycle (revised efficiency). Here are some popular chips: Chip andTotal work megahertzaccomplishedChip's priceMotherboard's price 8088-4.77 .2385 $3 $53 8088-10 .5 $4 $54 8086-10 .6 $5 $55 286-6 1.8 $10 $60 286-8 2.4 $12 $62 286-10 3 $14 $64 286-12 3.6 $16 $66 286-16 4.8 $20 $70 286-20 6 $25 $75 386SX-16 6.4 $30 $80 386SX-20 8 $35 $85 386SX-25 10 $40 $90 386SX-33 13.2 $45 $95 386SX-40 16 $50 $100 386DX-40 20 $60 $120 486SX-25 25 $80 $160 486SX-33 33 $100 $180 486DX-33 39.6 $260 $340 486DX-40 48 $270 $350 486DX2-50 55 $290 $370 486DX2-66 72.6 $390 $470 486DX4-75 81 $580 $660 486DX4-100108 $690 $770 Pentium-60132 $700 $1060 Pentium-66145.2 $800 $1160 Pentium-90198 $940 $1300 For example, look at the chart's bottom line. It says you can buy a Pentium chip running at 90 megahertz. Its ``total work accomplished'' is 198 (because 90 megahertz times the chip's revised efficiency of 220% is 198). You can buy it for $940 from discount dealers (who advertise in magazines such as Computer Shopper). For $1300, you can buy an entire 486DX2 motherboard; that price includes the Pentium-90 chip, ROM memory chips, and lots of other circuitry but not RAM memory chips (which cost extra and must be put onto the board to make the board work). Notice that the most expensive chip, the Pentium-90, has a total-work-accomplished rating of 198. The cheapest chip, the 8088-4.77, has a total-work-accomplished rating of just .2385. That means the Pentium-90 can accomplish about 830 times as much work as the 8088-4.77. But for a chip to accomplish anything at all, you must give it some work to do! If the chip must wait for you to tell it what to do, the chip accomplishes nothing useful during the wait: it just mumbles to itself. So to make full use of a Pentium-90, make sure you know what commands to give the computer and make sure you help the chip reach its full potential by buying quick RAM, quick disk drives, and a quick printer. Otherwise, the Pentium-90 will act as idiotic as if it's in the army: it will just ``hurry up and then wait'' for the other parts of the system to catch up and tell it what to do next. A mind is a terrible thing to waste! To avoid wasting the computer's mind (the CPU), make sure the other computer parts are fast enough to match the CPU and keep it from waiting. If you get suckered into buying a computer that has a Pentium-90 chip but a slow RAM, slow disk drives, and a slow printer, you've bought a computer that's just half-fast; it's half-assed. Those prices are what mail-order chip suppliers charge you for a single chip or motherboard to pop into your computer. Your computer's manufacturer buys at least 1000 microprocessors or motherboards at a time and gets a quantity discount. When you buy a microcomputer, its advertised price always includes a microprocessor, motherboard, and other goodies. Pay for the microprocessor separately only if you're inventing your own computer, or if you buy a computer that breaks and needs new parts, or you want to upgrade your computer by switching to a faster microprocessor and motherboard. Although the microprocessor is cheap, the computer containing it can cost thousands of dollars. That's because the microprocessor is just a tiny part of the computer. In addition to the microprocessor, you need memory chips, interface chips, and support chips; you also need PC boards to put the chips on; you also want I/O devices (keyboard, screen, printer, speaker, and mouse), disks, and software. Discount dealers sell IBM clones for these prices: Chip Complete computer 8088 $150 8086 $200 286 $400 386SX $600 386DX $700 486SX $1000 486DX $1300 486DX2 $1600 486DX4 $1900 Pentium-60 $2300 Pentium-66 $2600 Pentium-90 $2900 Those prices include almost everything you need. For example, they include the CPU, memory chips, disks, keyboard, and a screen that displays lots of colors. Those prices do not include a printer or software. Those prices are approximate; the exact price you pay depends on the quality, speed, and size of the various components. Notice that a 286 computer costs $200 more than an 8086 computer. That's because a 286 computer includes a better CPU chip and also comes with a better keyboard, better screen, better memory chips, and better disks. Motorola Intel's biggest competitor is Motorola. It manufactures the 6809E microprocessor, the 68000 (which is faster and understands advanced commands), several souped-up versions of the 68000, and the Power PC: Chip PriceComputers that use it 6809E $3 Radio Shack Color Computer 68000 $9 Mac, Mac Plus, Mac SE, Mac Classic, Amiga (500, 600, 1000, 2000), Atari ST 68020 $45 Mac LC, old Mac 2, Amiga 1200 68030 lotsMac (SE/30, Classic 2, LC 2, LC 3), new Mac 2, Amiga 2500 & 3000 68040 lotsMac Centris, Mac Quadra, and Amiga 4000 Power PClotsPower Mac Motorola's microprocessors are not Intel clones. They use different commands than Intel and require different software. When fed the proper software, they work as fast as Intel's microprocessors: Motorola's 6809E is about as fast as Intel's 8080 (which was the predecessor to the 8088) Motorola's 68000 is about as fast as Intel's 8086 Motorola's 68020 is about as fast as Intel's 286 Motorola's 68030 is about as fast as Intel's 386 Motorola's 68040 is about as fast as Intel's 486 Motorola's Power PC is about as fast as Intel's Pentium What's the Power PC? Motorola's fastest microprocessor, the Power PC, was invented by a team of researchers from three companies (Motorola, Apple, and IBM), all working together. That's why it's called the love-triangle chip. It was invented to prevent Intel from monopolizing the microcomputer marketplace. The first version of the Power PC is called the Power PC 601. It's manufactured just by IBM. Later versions, such as the Power PC 603, the Power PC 604, and the Power PC 620, will be manufactured by both Motorola and IBM. The Power PC is used in Apple's fastest computer (the Power Mac) and will also be used in fast computers that IBM is developing. Intel emulation Suppose your computer's microprocessor is made by Motorola, but somebody gives you software that's written for Intel microprocessors instead. You can run that software on your computer if you feed your computer an Intel emulator (software that makes Motorola microprocessors imitate Intel's). But Intel emulator software runs slowly. To accomplish tasks faster, buy software that runs directly on Motorola microprocessors without needing an Intel emulator. Math coprocessor Want a Motorola math coprocessor? For the 6809E CPU, no math coprocessor is available. For the 68000 or 68020, buy the 68881 math coprocessor ($49). For the 68030, buy the 68882 math coprocessor ($69). The 68040 comes in two versions: the standard version (called the 68RC040) includes math-coprocessor circuitry; the stripped-down version (called the 68LC040) does not. The Power PC includes math-coprocessor circuitry. Classic microprocessors Primitive old microcomputers contain microprocessors invented by Zilog and MOS Technology. They're not Intel clones. Zilog, which is owned by Exxon, makes the Z-80A microprocessor, which is super-cheap: it costs just $2! It's in many obsolete computers, such as the Radio Shack TRS-80 models 1 & 2 & 3 & 4 & 12, the Kaypro 2 & 4 & 10, the Epson QX-10 & Geneva, the Timex-Sinclair 1000 & 1500, and the Coleco Adam. The 6502 microprocessor is available from its inventor (MOS Technology, which is part of Commodore) and from other chip makers. You can also get souped-up versions, which understand extra commands and go faster! ChipPriceComputers that use it 6502 $2 Apple 2, Apple 2+, old Apple 2e, and Atari 800 65C02 $7Apple 2c, Apple 2c+, and new Apple 2e 6510$15 Commodore 64, Commodore 128, and Commodore Vic 65C816$17Apple 2GS The 65C02 and the 65C816 are made of CMOS; that's why their names contain the letter C. The other chips in that table are traditional: they're made of NMOS. How many pins? A cheap microprocessor (such as an 8088, 8086, Z-80, 6502, or 6809E) comes in a DIP (caterpillar) that has 40 pins (20 pairs of pins). Fancier chips have more pins. For example, the Motorola 68000 comes in a DIP that has 64 pins. If a chip is even fancier (such as the 68-pin Intel 286 or the 132-pin Intel 386DX), it requires too many pins to fit in a DIP. Instead of coming in a DIP, the chip usually comes in a pin grid array (PGA), which is a square having many pins underneath it, as if it were a square porcupine lying on its back. MEMORY CHIPS Although the CPU (the computer's brain) can think, it can't remember anything. It can't even remember what problem it was working on! Besides buying a CPU, you must also buy memory chips, which remember what problem the CPU was working on. To find out what the problem was, the CPU looks at the memory chips frequently ___ about a million times every second! The part of the computer's main circuitry that contains the memory chips is called the main memory. The typical memory chip comes in a DIP that has 8 pairs of legs (16 pins). In a typical microcomputer, the motherboard contains lots of memory chips. If you buy extra memory chips (so that your computer can remember extra information), and the extra memory chips don't all fit on the motherboard, you must buy an extra PC card to mount them on; that extra card is called a memory card. If the memory card comes in a cute little cartridge that you can pop into and out of the computer easily, it's called a memory cartridge. Warning: if you buy a memory chip or card or cartridge, and want to pop it into the computer, turn off the computer's power first. If you forget, and accidentally leave the power on while you're inserting (or removing) the memory, you might wreck your computer! You need two kinds of memory chips: RAM and ROM. The RAM chips remember information temporarily; the ROM chips remember information permanently. Let's begin by looking at RAM chips. RAM If a chip remembers information just temporarily, it's called a random-access memory chip (RAM chip). When you buy RAM chips, they contain no information yet; you tell the CPU what information to put into them. Later, you can make the CPU erase that information and insert new information instead. The RAM chips hold information just temporarily: when you turn the computer's power off, the RAM chips are automatically erased. Whenever the CPU tries to solve a problem, the CPU stores the problem in the RAM chips, temporarily. There it also stores all instructions on how to solve the problem; the instructions are called the program. If you buy more RAM chips, the CPU can handle longer problems and programs. If the computer doesn't have enough RAM chips to hold the entire problem or program, you must split the problem or program into several shorter ones instead, and tell the CPU to work on each of the short ones temporarily. How RAM is measured A character is any symbol you can type on the keyboard, such as a letter or digit or punctuation mark or blank space. For example, the word HAT consists of 3 characters; the phrase Mr. Poe consists of 7 characters (M, R, the period, the space, P, O, and E). The phrase LOVE 2 KISS U consists of 13 characters. Instead of saying ``character'', hungry programmers say byte. So LOVE 2 KISS U consists of 13 bytes. If, in the RAM, you store LOVE 2 KISS U, that phrase occupies 13 bytes of the RAM. RAM chips are manufactured by a process that involves doubling. The most popular unit of RAM is ``2 bytes times 2 times 2 times 2 times 2 times 2 times 2 times 2 times 2 times 2'', which is 1024 bytes, which is called a kilobyte. So the definition of a kilobyte is ``1024 bytes''. Although a kilobyte is exactly 1024 bytes, the following approximations are useful. A kilobyte is about a thousand bytes. It's about how many characters you see on the screen of a TV computer. It's about half as many characters as you see on the screen of an 80-column monitor. It's about a quarter as many characters as you get on a typewritten page (assuming the page is single-spaced with one-inch margins and elite type). The abbreviation for kilobyte is K. For example, if a salesperson says the computer has a ``64K RAM'', the salesperson means the main circuitry includes enough RAM chips to hold 64 kilobytes of information, which is slightly over 64,000 bytes. A megabyte is 1024 kilobytes. Since a kilobyte is 1024 bytes, a megabyte is ``1024 times 1024'' bytes, which is 1,048,576 bytes altogether, which is slightly more than a million bytes. It's about how much you can fit in a 250-page book (assuming the book has single-spaced typewritten pages). The abbreviation for megabyte is meg or M. A gigabyte (pronounced ``gig a bite'') is 1024 megabytes. It's slightly more than a billion bytes. A terabyte is 1024 gigabytes. It's slightly more than a trillion bytes. In honor of the words ``kilobyte'', ``megabyte'', ``gigabyte'', and ``terabyte'', many programmers name their puppies Killer Byte, Make a Byte, Giggle Byte, and Terror Byte. Rows of RAM chips In a cheap microcomputer (such as the Commodore 64), the RAM is a row of eight NMOS chips. That row of chips holds 64K altogether. So it holds 64 kilobytes, which is slightly more than 64 thousand bytes (since a kilobyte is slightly more than a thousand bytes). That row of chips is called a 64K chip set. Each chip in that set is called a ``64K chip'', but remember that you need a whole row of those 64K chips to produce a 64K RAM. Mail-order discount dealers charge 50¢ for a 64K chip. So to get 64K of RAM, you need a 64K chip set, which is a row of eight 64K chips, which costs ``8 times 50¢'', which is $4. The most popular style of 64K chip is the TI 4164. Although that style was invented by Texas Instruments, other manufacturers have copied it. If your computer is slightly fancier (such as the Apple 2c), it has two rows of 64K chips. Since each row is a 64K RAM, the two rows together total 128K. If your computer is even fancier, it has many rows of 64K chips. For example, your computer might have four rows of 64K chips. Since each row is a 64K RAM, the four rows together total 256K. 64K chips didn't become popular until 1982. If your computer was built before then, it probably contains inferior chips: instead of containing a row of 64K chips, it contains a row of 16K chips or 4K chips. During the 1980's, computer engineers invented 256K and 1M chips. The most popular style of 256K chip is called the 41256, which you can get from discount dealers for $2. A 1M chip costs $6. If your computer has very little RAM, you can try to enlarge the RAM, by adding extra rows of RAM chips to the motherboard. But if the motherboard's already full, you must buy an extra PC card to put the extra chips on. That extra PC card is called a RAM memory card. Parity chip The IBM PC and some clones contain an extra chip in each row, so that each row contains 9 chips instead of 8. The row's ninth chip is called the parity chip. It double-checks the work done by the other 8 chips, to make sure they're all working correctly! So for an IBM PC or one of those clone, you must buy 9 chips to fill a row. SIMMs and SIPPs If your computer is ultra-modern and you want to insert an extra row of RAM chips, you do not have to insert 8 or 9 separate chips. Instead, you can buy a strip that contains all 8 or 9 chips and just pop the whole strip into the computer's motherboard, in one blow. The typical strip of chips is called a Single In-line Memory Module (SIMM) and pops into one of the motherboard's slots. If the strip pops into a series of pinholes instead, the strip is called a Single In-line Pin Package (SIPP). Discount dealers charge $15 for a SIMM that holds 256K, $39 for a SIMM that holds a megabyte, $148 for a SIMM that holds 4 megabytes. SIPPs cost $5 more than SIMMs. Some computers use SIMMs containing a set of just 2, 3, or 4 chips. That set of chips is special and imitates 8 or 9 normal chips. In old-fashioned computers, each SIMM fits into a motherboard slot by using 30 big pins. In computers that are more modern, each SIMM uses 72 big pins instead. The typical SIMM contains chips that are fast: they retrieve information in 70 nanoseconds. (A nanosecond is a billionth of a second.) Old-fashioned SIMMs contain slower chips, requiring 80 nanoseconds; the fanciest SIMMs contains extra-fast chips, requiring just 60 nanoseconds. If you want to buy an extra SIMM to put in your computer, make sure you buy the same kind of SIMM as the other SIMMs that are already in your computer. Make sure the extra SIMM has the same number of pins (30 or 72?), the same number of chips on it (2, 3, 4, 8, or 9?), and operates at the same number of nanoseconds (80, 70, or 60?). Let your memory grow In a typical computer, the RAM contains several rows of chips, so that the total RAM contains several megabytes. Here's how much RAM you typically get altogether: Computer's priceTypical quantity of RAM $75-$100 64K (64 kilobytes, 65,536 bytes) $100-$125 128K(128 kilobytes, 131,072 bytes) $125-$150 256K(256 kilobytes, 262,144 bytes) $150-$400 512K(512 kilobytes, 524,288 bytes) $400-$650 1M (1 megabyte, 1,048,576 bytes) $650-$900 2M (2 megabytes, 2,097,152 bytes) $900-$1,600 4M (4 megabytes, 4,194,304 bytes) $1,600-$2,800 8M (8 megabytes, 8,388,608 bytes) $2,800-$5,000 16M (16 megabytes,16,777,216 bytes) Mac The original Mac (nicknamed the Slim Mac) included 128K of RAM. Then came a version nicknamed the Fat Mac, which included 512K. Next came an improvement called the Mac Plus, which included 1M. Those Macs are obsolete. All Macs sold today come with at least 4M, which is what you need to run modern Mac software well. Names of classic computers The Commodore 64 computer got its name because it contained 64K of RAM. Then Commodore invented an improved version, the Commodore 128, which contained 128K of RAM. The Laser 128 imitates the Apple 2c. Each comes with 128K of RAM. IBM The original IBM PC came with just 16K of RAM, but you could add extra RAM to it. Here's how much RAM the typical IBM PC or clone contains now: CPU Typical quantity of main RAM 8088 512K or 640K 286 640K or 1M 386 2M or 4M 486 4M or 8M Pentium 8M or 16M To run modern IBM PC software well, you need at least 4M of main RAM. To run the FANCIEST modern IBM PC software well, you need at least 8M. For computers having lots of RAM, here's how it's divvied up. . . . The first 640K of main RAM is called the base memory (or conventional memory). That's the part of the RAM that the computer can handle easily and quickly. The next 384K is called upper memory. It's relatively unimportant, since most programs don't know how to use it. Those two parts (the conventional memory and the upper memory) consume a total of 640K+384K, which is 1024K, which is one megabyte. The rest of the main RAM (beyond that first megabyte) can be either expanded or extended. Here's the difference between ``expanded'' and ``extended''. . . . Expanded RAM is old-fashioned. Extended RAM is modern. (To remember that, notice that the word ``expanded'' comes before ``extended'' in the dictionary.) Expanded RAM runs slowly. Extended RAM runs fast. Expanded RAM can be added to any IBM-compatible computer. Extended RAM requires a modern CPU (a 286, 386, or 486) and will not run on an 8088 or 8086 CPU. Modern programs work best if you have modern RAM (extended). Old-fashioned programs don't understand extended RAM; they understand just old-fashioned RAM (expanded). Since most programs sold today are still old-fashioned, expanded RAM is more useful than extended RAM. To run both kinds of programs, you should buy both kinds of RAM. Some primitive programs use just the 640K of conventional RAM. They don't understand how to use expanded or extended RAM at all. Expanded RAM and extended RAM are both built from the same kind of NMOS RAM chips. Whether a chip acts as ``expanded'' or ``extended'' RAM depends just on what other hardware and software you bought to control those chips. If a chip acts as ``extended'' RAM, the CPU gets information from that chip directly and fast. If a chip acts as ``expanded'' RAM, the CPU gets the chip's information by copying that information to the upper memory area. Then the CPU examines what's in the upper memory area. That process is slow, since you must wait for the CPU to copy the chip's information to the upper memory area. That process was invented because it's the only way an 8088 or 8086 chip can handle RAM beyond a megabyte. Extended RAM is faster and simpler but requires a 286, 386, 486, or Pentium ___ and is understood just by programs that are modern. For an 8088 or 8086 CPU, the expanded RAM comes on an expanded RAM card. That card contains the RAM chips and the hardware necessary to control them. That card is expensive. For a 286 CPU, you can buy an expanded RAM card, an extended RAM card (which is cheaper), or a combination card that you can switch between the two. For a 386, 486, or Pentium, you can put lots of RAM chips on the motherboard without buying any cards. The CPU normally treats those RAM chips as extended RAM; but you can run a program that makes those RAM chips imitate expanded RAM so that old-fashioned programs can use them. If you have a 386, 486, or Pentium and want to run even the fanciest software well, buy at least 8M of RAM. The computer will use the first megabyte for conventional RAM (640K) and the upper memory (384K). The computer will use the remaining seven megabytes for extended RAM but make some of that extended RAM imitate expanded RAM. A trio of companies (Lotus, Intel, and Microsoft) agreed on the technical details of how expanded memory should be handled. Their agreement is called the Lotus-Intel-Microsoft Expanded Memory Specification (LIM EMS). Expanded memory fitting their specification is called EMS memory. To manage that expanded memory, you need a special program, called the expanded memory manager (EMM). The same trio of companies, working together with a fourth company (AST), developed an agreement on extended memory. Their agreement is called the Lotus-Intel-Microsoft-AST eXtended Memory Specification (or LIMA XMS). Extended memory fitting their specification is called XMS memory. To manage that extended memory, you need a program called the extended memory manager. The most popular extended memory manager is called ``HIMEM.SYS''. The first 64K of extended memory is called the high memory area (HMA), because it's just slightly higher than the base memory and upper memory. (The rest of the extended memory should be called ``even higher memory'', but nobody does.) NMOS RAM versus CMOS Most RAM chips are NMOS. The prices I quoted you were for NMOS. If your computer operates on batteries, it uses CMOS instead, which consumes less electricity than NMOS. Unfortunately, CMOS chips cost more than NMOS. A 64K chip costs 50¢ if made of NMOS, but costs $4 if CMOS. Dynamic versus static A RAM chip is either dynamic or static. If it's dynamic, it stores data for only 2 milliseconds. After the 2 milliseconds, the electrical charges that represent the data dissipate and become too weak to detect. When you buy a PC board containing dynamic RAM chips, the PC board also includes a refresh circuit. The refresh circuit automatically reads the data from the dynamic RAM chips and then rewrites the data onto the chips before 2 milliseconds go by. Every 2 milliseconds, the refresh circuit reads the data from the chips and rewrites the data, so that the data stays refreshed. If a chip is static instead of dynamic, the electrical charge never dissipates, so you don't need a refresh circuit. (But you must still keep the power turned on.) In the past, computer designers were afraid that the dynamic RAM's refresh circuit wouldn't work, and used static RAM instead. But today, refresh circuits are reliable, and the most popular kind of RAM is dynamic NMOS. For example, the TI 4116, 4164, and 41256 are all dynamic NMOS. Dynamic RAM is called DRAM. So when an engineer says ``give me a DRAM'', he doesn't mean a liqueur, at least not yet. Static NMOS is still available. CMOS and bipolar are always static. Bipolar cache In a maxicomputer, minicomputer, or fancy microcomputer, the RAM is divided into two sections. One section is huge, contains many rows of NMOS chips, and is called the main RAM. The other section is tiny, contains just a few bipolar chips, and is called the cache (which is pronounced ``cash''). The cache's bipolar chips work much faster than the main RAM's NMOS chips. In most IBM clones containing a 486DX, the NMOS chips retrieve information in 70 nanoseconds, and the bipolar chips take between 15 and 20 nanoseconds. Unfortunately, the cache's bipolar chips are very expensive and hold just a few K. In most IBM clones containing a 486DX, the main RAM holds 4M or 8M; but the cache holds just 128K or 256K. So the bipolar cache is a super-fast, super-expensive memory that's small. In the bipolar cache, the computer keeps a copy of the main RAM's information that you've been using recently, so the CPU can grab that information again super-quickly. s and facts put there by the manufacturer, and it remembers that info forever, even if you turn off the power. Here's the difference between RAM and ROM: RAM chips remember, temporarily, info supplied by you. ROM chips remember, forever, info supplied by the manufacturer. The typical computer includes many RAM chips (arranged in rows) but just a few ROM chips (typically 6). What kind of info is in ROM? In your computer, one of the ROM chips contains instructions that tell the CPU what to do first when you turn the power on. Those instructions are called the ROM bootstrap, because they help the computer system start itself going and ``pull itself up by its own bootstraps''. In the typical microcomputer, that ROM chip also contains instructions that help the CPU transfer information from the keyboard to the screen and printer. Those instructions are called the ROM operating system or the ROM basic input-output system (ROM BIOS). In the typical microcomputer, one of the ROM chips tells the computer how to make each character on the screen out of dots. That chip is called the character generator. In famous old microcomputers, several ROM chips contain definitions of fundamental English words, which are called BASIC words. For example, those ROM chips contain the definitions of BASIC words such as PRINT, NEW, RUN, LIST, GO, TO, END, STOP, INPUT, IF, and THEN. Those BASIC definitions in the ROM are called the ROM BASIC interpreter. Commodore 64 For example, let's look inside a primitive computer: the Commodore 64. It contains just four ROM chips. The first chip contains 8K, for the ROM bootstrap and ROM BIOS. The second contains Commodore's 8K ROM BASIC. The third contains Commodore's 4K character generator. The fourth contains ¼K that tells the computer how to make the screen produce pretty colors. IBM In the typical IBM PC or clone, the motherboard contains a ROM BIOS chip. That chip contains the ROM BIOS and also the ROM bootstrap. If your computer is manufactured by IBM, that chip is designed by IBM; if your computer is a clone, that chip is an imitation designed by a company such as Phoenix. Such a chip designed by Phoenix is called a Phoenix ROM BIOS chip. Other companies that design ROM BIOS chips for clones are American Megatrends Incorporated (AMI), Award (a smaller company), and Quadtel (which is now owned by Phoenix.) On a special PC card (called a video display card), you'll find a ROM chip containing the character generator. If your computer is built by IBM, some chips on the motherboard contain the ROM BASIC interpreter. If your computer is a clone, all of BASIC comes on a disk instead of in ROM chips. Altogether, the original IBM PC contained six ROM chips: the ROM BIOS chip, the character generator, and four ROM BASIC interpreter chips. Each of those six chips contained 8K, so that the computer's ROM totaled 48K. On newer computers from IBM and clones, the total is slightly different. Extra ROM chips Some microcomputers include extra ROM chips that tell the computer how to handle specific applications, such as word processing and accounting. ROM cartridges If your computer attaches to a TV and is old-fashioned (such as a Commodore Vic, Commodore 64, Commodore 128, Atari 800, Atari 800XL, or Radio Shack Color Computer), you can pop ROM cartridges into the computer. A ROM cartridge is a cartridge containing a PC card full of ROM chips. Etched into those ROM chips is a program. The typical ROM cartridge contains a program that plays a video game, such as Space Invaders or Pac Man or computer chess. You can also buy ROM cartridges that contain programs for word processing, music, art, or tutoring you. Each ROM cartridge costs about $30. How ROM chips are made The info in a ROM chip is said to be burned into the chip. To burn in the info, the manufacturer can use two methods. One method is to burn the info into the ROM chip while the chip's being made. A ROM chip produced by that method is called a custom ROM chip. An alternate method is to make a ROM chip that contains no info but can be fed info later. Such a ROM chip is called a programmable ROM chip (PROM). To feed it info later, you attach it to a device called a PROM burner, which copies info from a RAM to the PROM. Info burned into the PROM can't be erased, unless the PROM's a special kind: an erasable PROM (EPROM). To erase a typical EPROM, shine an intense ultraviolet light at it for 20 minutes. That's called an ultraviolet-erasable PROM (UV-EPROM). A fancier kind of EPROM can be erased quickly by sending it a 25-volt shock for a tenth of a second. That's called an electrically erasable PROM (EEPROM) or electrically alterable PROM (EAPROM). After you erase an EPROM, you can feed it new info. If you're a manufacturer designing a new computer, begin by using an erasable PROM (EPROM), so you can make changes easily. When you decide not to make any more changes, switch to a non-erasable PROM, which costs less to manufacture. If your computer becomes so popular that you need to manufacture over 10,000 copies of the ROM, switch to a custom ROM, which costs more to design and ``tool up for'' but costs less to make copies of.ROMIf a chip remembers information permanently, it's called a read-only memory chip (ROM chip), because you can read the information but can't change it. The ROM chip contains permanent, eternal truth