
           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 " 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 ``386'' 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 K 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