
                  FUNDAMENTALS
  Memory comes in three popular forms: RAM chips, ROM chips, and 
disks.
  You already learned about RAM chips and ROM chips. Let's 
examine disks.
  A computer disk is round, like a phonograph record.

                   Three kinds
  You can buy three popular kinds of computer disks:
A floppy disk is made of flimsy material. It's permanently 
encased in a sturdy, square dust jacket.
A hard disk is made of firmer material. It typically hides in 
your computer permanently, unseen.
A CD-ROM is a compact disk. It's the same kind of CD compact disk 
that plays music.
  Each kind has its own advantages and disadvantages.
  Floppy disks are the cheapest (about 50 per disk) and the 
easiest to mail to your friends: just stick the floppy disk in an 
envelope, perhaps with some padding. Unfortunately, floppy disks 
work the most slowly, and they hold the least data: the typical 
floppy disk holds about 1 megabyte, while the typical hard disk 
or CD-ROM can hold many hundreds of megabytes.
  Hard disks work the fastest ___ over 20 times faster than the 
other kinds! But hard disks are also the most expensive.  
Moreover, they typically can't be removed from your computer and 
therefore can't be mailed to your friends.
  CD-ROMs are the best value: CD-ROM disks cost less than 1 per 
megabyte to manufacture. But they have a frustrating limitation: 
the information on CD-ROM disks cannot be edited.
  Since each kind of disk has its own advantages and 
disadvantages, you'll want to buy all three kinds.

                    Spelling
  Computer experts argue about spelling. Some experts write 
``disk'', others write ``disc''.
  Most manufacturers write ``disk'' when referring to floppy 
disks or hard disks, but write ``disc'' when referring to 
CD-ROMs. That inconsistency annoys me.
  To be more consistent, I'll always write ``disk'', even when 
referring to CD-ROMs. Most computer magazines (such as PC 
Magazine and PC World) feel the same way I do: they always write 
``disk''. The growing tendency is to always write ``disk''.
  For hard disks, IBM used to write ``disc'' but now writes 
``disk''.

      FLOPPY DISKS
                                                     A floppy 
disk (or diskette) is round but comes permanently sealed in a 
square dust jacket. (Don't try to remove the floppy disk from its 
square jacket.)
                                                     The floppy 
disk is as thin and flimsy as a sheet of paper but is protected 
by the sturdy, square jacket that encases it.

                                                          Three sizes
                                                     Floppy disks 
come in three sizes.
                                                     The most 
popular size is called a 3-inch floppy disk, because it comes in 
a square jacket that's about 3 inches on each side. (Actually, 
each side of the jacket is slightly more than 3 inches, and the 
disk's diameter is slightly less.)
                                                     An older 
size, used mainly on older computers, is called 5-inch. It comes 
in square jacket that's exactly 5 inches on each side.
                                                     An even 
older size, 8-inch, is used just on ancient computers that are no 
longer built.
                                                     Those three 
sizes have nicknames:
An 8-inch floppy disk is called a large floppy.
A 5-inch floppy disk is called a minifloppy.
A 3-inch floppy disk is called a microfloppy.

                                                         Jacket colors
                                                     The jacket 
of a 5-inch or 8-inch floppy disk is usually black. The jacket 
of a 3-inch floppy disk is usually black, blue, white, or beige 
(very light grayish brown).
                                                     If you pay a 
surcharge, you can get jackets that have wilder colors.

                                                            History
                                                     8-inch 
floppies were invented in the early 1970's by IBM. 5-inch 
floppies were invented in the late 1970's by Shugart Associates, 
which later became part of Xerox.
  3-inch floppies were invented in the 1980's by Sony. They've 
become the most popular size because they're the smallest, 
cutest, and sturdiest. They're small enough to fit in the pocket 
of your shirt, cute enough to impress your friends, and sturdy 
enough to survive when you fall on your face. They're also easy 
to mail, since they're small enough to fit in a standard white 
business envelope and sturdy enough to survive the U.S. Postal 
System. Yup, nice things come in small packages!

           Magnetized iron
  The round disk (which hides inside the square jacket) is coated 
with rust, so it looks brown. Since the rust is made of iron, 
which can be magnetized, the disk stores magnetic signals. The 
pattern of magnetic signals is a code representing your data.

               Drives
  To use a floppy disk, you must buy a floppy-disk drive, which 
is a computerized record player.
  If the drive is external, it's a box sitting near the computer. 
If the drive is internal, it's built into the middle of the 
computer.
  The drive has a slit in its front side. To use the drive, push 
the disk (including its jacket) into the slit.
  When pushing the sheathed treasure into the box's slit, don't 
shove too hard. Oooh! Please be gentle!
  When you push your disk into the slit, don't push the disk in 
backwards or upside-down! Here's how to push the disk in 
correctly. . . . 
  First, notice that the disk's jacket has a label on it and also 
has a big oval cutout. (If the disk is 3-inch, the cutout is 
covered by a metal slider.) Insert the disk so that the oval 
cutout goes into the drive before the label does. If the drive's 
slit is horizontal, make sure the label is on the top side of the 
jacket; if the drive is vertical, make sure the label is on the 
left side of the jacket.
  After putting the disk into the slit, close the latch to cover 
the slit. (If the disk is 3-inch, there is no latch.) Since the 
slit and latch act as a door, closing the latch is called closing 
the door.
  As soon as you close the door, the disk drive automatically 
positions the disk onto the turntable that's hidden inside the 
drive. The turntable's called the spindle. It can spin the disk 
quickly.
  Like a record player, the disk drive contains an arm with a 
``needle'' on it. The needle is called the read-write head, 
because it can read what's on the disk and also write new 
information onto the disk.
  Here's how to write new information onto the disk. Put your 
fingers on the computer's keyboard. Type a command that tells the 
computer you want to use the disk. Then type the information you 
want to transfer to the disk.
  To transfer the information to the disk, the computer lowers 
the read-write head onto the disk. An electrical charge passes 
through the head. The charge creates an electromagnetic field, 
which magnetizes the iron on the disk's surface. Each iron 
particle has its own north and south pole; the patterns formed by 
the north and south poles are a code that stands for the 
information you're storing.
  Tracks As the disk spins, the head remains stationary, so that 
the head draws a circle on the spinning disk's surface. The 
circle's called a track. To draw the circle, the head doesn't use
ink; instead, it uses a pattern of magnetic pulses. Since your 
eye can't see magnetism, your eye can't see the circle; but it's 
there!
                                         When you start using a 
blank disk, the arm puts the head near the disk's outer rim, so 
that the head's track (circle) is almost as wide as the disk. 
That track's called track 0.
                                         Then the arm lifts the 
head, moves the head slightly closer to the virgin disk's center, 
and puts the head back down onto the disk again. The head draws 
another circular track on the disk, but this new circular track 
is slightly smaller than the previous one. It's called track 1.
                                         Then the head draws 
track 2, then track 3, then track 4, and so on, until the head 
gets near the center of the disk, and draws the last circular 
track (which is smaller than the other tracks).
                                         To organize the 
information on a track, the computer divides the track into 
sectors. Each ``sector'' is an arc of the circle.
                                         Single-sided versus 
double-sided drives A modern disk drive has two read-write heads. 
One head uses the disk's top surface, while the other head uses 
the disk's bottom, so that the drive can use both sides of the 
disk simultaneously. That's called a double-sided disk drive. The 
drive puts information onto the disk by first using track 0 of 
the main side, then track 0 of the flip side, then track 1 of the 
main side, then track 1 of the flip side, etc.
                                         If a disk drive is not 
modern ___ if it's ancient and primitive ___ it has just one 
read-write head, which uses just one side of the disk. The flip 
side of the disk is unused. That kind of drive is called a 
single-sided disk drive. Which side of the disk does the drive 
use? Though some drives use the side that has the label, other 
drives (by other manufacturers) use the side opposite the label 
instead.
                                         Double-sided is also 
called DS and 2-sided and 2S. Single-sided is also called SS and 
1-sided and 1S.
                                         Capacity How many 
kilobytes can you fit on a floppy disk? The answer depends on 
which kind of drive you have.
                                         The most popular kind of 
drive is called a 3-inch high-density floppy drive. Here's how 
it works.
                                         It holds a 3-inch 
floppy disk. It writes on both sides of the disk simultaneously, 
since it's a double-sided disk drive. It writes 80 tracks on each 
side. It divides each track into 18 sectors. Each sector holds 
``512 bytes'', which is half a kilobyte, K.
                                         Since the disk has 2 
sides, 80 tracks per side, 18 sectors per track, and K per 
sector, the disk's total capacity is ``2 times 80 times 18 times 
K'', which is 1440K. So altogether, the disk holds 1440K. That's 
called 1.44M (where an M is defined as being 1000K). That's why a 
3-inch high-density floppy drive is also called a 1.44M drive.
                                         The kind of disk you put 
into it is called a 1.44M floppy disk (or a 3-inch high-density 
floppy disk). Since the disk holds 1.44M (which is 1440K), and 
since a K is 1024 bytes, the disk holds ``1440 times 1024'' 
bytes, which is 1,474,560 bytes altogether. That's a lot of 
bytes!
                                         Although the disk holds 
1440K, some of those K are used for ``bureaucratic overhead'' 
(such as holding a directory that reminds the computer which data 
is where on your disk). A Mac uses just 1 sector (K) for 
bureaucratic overhead. An IBM-compatible computer uses 33 sectors 
(16K) for bureaucratic overhead, leaving just 1423K (1,457,664 
bytes) for your data.
  When you buy a blank disk to put in a 1.44M drive, make sure 
the disk is the right kind. Make sure the disk is 3-inch; and to 
get full use of what the drive can accomplish, make sure the disk 
is high-density! The abbreviation for ``high-density'' is HD. A 
high-density 3-inch disk has the letters HD stamped in white on 
its jacket; but the H overlaps the D, so it looks like this: HD. 
Also, a high-density 3-inch disk has an extra square hole cut 
through its jacket.
  Old computers use inferior floppy drives, whose capacities are 
less than 1.44M.
A capacity that's less than 150K is called single-density (SD).
A capacity bigger than 150 but less than 1M is called 
double-density (DD).
A capacity bigger than 1M is called high-density (HD).
Anything less than high-density is called low-density.
  Although the jacket of a high-density 3-inch disk has ``HD'' 
stamped on them and an extra hole punched through it, the jackets 
of other kinds of disks often lack any distinguishing marks. Too 
bad!
  Popular IBM-compatible drives For IBM-compatible computers, 
four kinds of floppy drives have been popular:
IBM drive's nameCapacity  Details
5-inch double-density 360K40 tracks per side,  9 sectors per 
track
5-inch high-density1200K (which is 1.2M)80 tracks per side, 15 
sectors per track

3-inch double-density 720K80 tracks per side,  9 sectors per 
track
3-inch high-density1440K (which is 1.44M)80 tracks per side, 18 
sectors per track
  Each of those IBM-compatible drives is double-sided and has K 
per sector. They're manufactured by companies such as TEAC, NEC, 
and Chinon.
  The fanciest drives (3-inch high-density) used to be 
expensive, but now you can buy them for just $49 from mail-order 
discount dealers (such as Insight at 1912 W. Fourth St., Tempe AZ 
85281, phone 800-998-8028 or 602-902-1176).
  Mac drives For Mac computers, three kinds of floppy drives have 
been popular:
Mac drive's nameCapacity  Details
1-sided double-density 400K1 side, 8-12 sectors per track
2-sided double-density 800K2 sides, 8-12 sectors per track
high-density  1440K (which is 1.44M)2 sides, 18 sectors per track
Each Mac drive is 3-inch and has 80 tracks per side, K per 
sector. The Mac's high-density drive is called the Mac 
Superdrive.
  On a disk, the inner tracks have smaller diameters than the 
outer tracks. Most drives squeeze as many sectors onto an inner 
track as onto an outer track, but the Mac double-density drives 
puts fewer sectors onto the inner tracks and put extra sectors 
onto the outer tracks. Specifically, the outer 16 tracks are 
divided into 12 sectors, the next 16 tracks into 11 sectors, the 
next 16 into 10, the next 16 into 9, and the inner 16 into 8.
  Drives for other computers For other computers, many kinds of 
floppy drives have been invented:
Computer    Drive capacityDetails
Apple 2 family140K    5", 1 side,  35 tracks, 16 sectors, K per 
sector

Tandy Color Computer157K5", 1 side,  35 tracks, 18 sectors, K 
per sector
Tandy Models 3, 4, 4P180K5", 1 side,  40 tracks, 18 sectors, K 
per sector
Tandy Model 4D360K    5", 2 sides, 40 tracks, 18 sectors, K per 
sector

Commodore 64170K     5", 1 side,  35 tracks, 17-21 sectors, K 
per sector
Commodore Amiga880K   3", 2 sides, 80 tracks, 11 sectors, K per 
sector
  For the Commodore 64, the 17 outer tracks are divided into 21 
sectors, the next 7 tracks into 19 sectors, the next 6 tracks 
into 18 sectors, and the inner 5 tracks into 17 sectors.
  Speed In the disk drive, the disk spins quickly. The exact 
speed depends on what size disk the drive uses.
Low-density 5-inch disks revolve 5 times per second. That makes 
300 revolutions per minute, 300 rpm.
8-inch disks and high-density 5-inch disks revolve faster: 6 
times per second (360 rpm).
3-inch disks revolve even faster: between 6 and 10 times per 
second.

                  Buying disks
  When you buy a floppy disk, make sure its size matches the size 
of the drive. For example, a 3-inch disk will not work in a 
5-inch drive.
                                                     If you buy a 
blank 5-inch floppy disk, you can stick it into any normal 
5-inch drive, regardless of who manufactured the drive and who 
manufactured the computer. But after you've put information onto 
the disk, that information is understandable only to your kind of 
computer. For example, an Apple 2e cannot understand what an IBM 
PC writes.
                                                     When you go 
into a computer store to buy a disk that contains software, tell 
the salesperson which kind of computer you have, so that the 
salesperson can give you a disk containing information 
understandable to your computer.
                                                     If your 
drive is single-density or double-density, it cannot handle 
high-density disks at all.
                                                     If your 
drive is 5-inch and high-density, it can read single-density and 
double-density disks, but it might have trouble writing new 
information onto them. So when buying blank disks for your 
5-inch high-density drive to write on, avoid buying 
single-density or double-density disks.
                                                     The three 
crummy kinds of 5-inch floppy disks (single-sided 
single-density, single-sided double-density, and double-sided 
double-density) are all manufactured by the same process as each 
other. The only difference is the manufacturer's ``guarantee'': a 
double-sided double-density disk is ``guaranteed'' to work on 
both sides and hold lots of data; a single-sided or 
single-density disk is not. Even if you buy a disk that has a 
poor guarantee (just ``single-sided single-density''), it 
typically works fine even if you use both sides and store lots of 
data. The only difference is that the manufacturer hasn't 
bothered testing the second side and hasn't bothered testing 
double-density data. During the 1970's and 1980's, single-sided 
single-density disks were significantly cheaper than double-sided 
double-density, but now the prices are about the same.
                                                     Formatting 
the disk Before you can use a blank floppy disk, its surface must 
be formatted (divided into tracks and sectors). Buy a disk that's 
been formatted already, or buy an unformatted disk and format it 
by typing a command on your computer's keyboard.
                                                     After the 
disk's been formatted, you can store whatever information you 
wish onto the disk. Do not tell the drive to format that disk 
again. If you accidentally make the drive format the same disk 
again, the drive will create new tracks and sectors on the disk, 
and erase the old tracks and sectors, and therefore erase all 
your old data!
  Remember:
If a disk is blank, format it before you use it.
If a disk already contains info, do not format it; it's been 
formatted already.
  Name brands The most famous manufacturers of floppy disks are 
Verbatim and Maxell. But instead of buying those brands, buy 
generic floppy disks instead. The generics cost less and 
typically work just as well.
  Discount dealers To get the lowest prices on generic floppy 
disks, contact MEI Micro Center (1100 Steelwood Rd., Columbus OH 
43212, 800-634-3478) or Diskettes Unlimited (6206 Long Dr., 
Houston TX 77087, 800-DOG-DISK).
  For example, here are the prices from MEI Micro Center for 
double-sided disks:
Kind of disk      100 disks1000 disks
5-inch double-density, unformatted$19+$1.20$160+$12
5-inch high-density,   unformatted$26+$1.20 $21+$12

3-inch double-density, unformatted$35+$2.40$290+$24
3-inch high-density,   formatted$41+$2.40$350+$24
Add up the prices of what you want, then add the handling charge 
($3.25). For example, for 100 of the best disks (3-inch 
high-density, formatted), MEI charges you $41 (for the disks) + 
$2.40 (shipping) + $3.25 (handling), which is $46.65. That's 
about 47 per disk. For 1000 of the best disks, MEI charges you 
$350 + $24 + $3.25, which is $377.25, which comes to about 38 
per disk. Diskettes Unlimited charges even less but might give 
you slightly lower quality; for details, phone them.
  What's a disk worth? Although you can buy a blank floppy disk 
for under 50, a disk containing information costs much more. The 
price depends on how valuable the information is. A disk that 
explains to the computer how to play a game costs about $40. A 
disk teaching the computer how to handle a general business task 
(such as accounting, filing, or correspondence) usually costs 
about $200.
  A disk containing intimate, personal data about your business's 
customers, suppliers, employees, and methods is worth even more 
___ perhaps thousands of dollars! To compute how much it's worth 
to you, imagine that you've lost it, or that it fell into the 
wrong hands!

         Protect your disks
  Most parts of a computer system are sturdy: even if you bang on 
the keyboard and rap your fist against the screen, you probably 
won't do any harm. Only one part of a computer system is 
delicate: that part is the disk. Unfortunately, the magnetic 
signals on your disk are easy to destroy.
  One way to accidentally destroy them is to put your disk near a 
magnet; so keep your disks away from magnets! For example, keep 
your disk away from paper clips that have been in a magnetized 
paper-clip holder. Keep your disk away from speakers (such as the 
speakers in your stereo, TV, and phone), because all speakers 
contain magnets. Keep your disk away from electric motors, 
because motors generate an electromagnetic field. So to be safe, 
keep your disk at least six inches away from paper clips, 
stereos, TV's, telephones, and motors.
  Keep your disk away from heat, because heat destroys the disk's 
magnetism and ``melts'' your data. So don't leave your disk in 
the hot sun; don't leave it on a sunny windowsill; don't leave it 
in the back of your car on a hot day. If your disk drive or 
computer feels hot, quickly lower the temperature, by getting an 
air conditioner or at least a fan.
  3-inch floppy disks come in strong jackets, but 5-inch and 
8-inch floppy disks come in jackets that are too weak and
thin to protect disks from pressure. Don't squeeze your disk. 
Don't put it under a heavy object, such as a paperweight or a 
book. If you want to write a note on the disk's jacket, don't use 
a ball-point pen (which crushes the disk); use a soft felt-tip 
pen instead.
                                         Keep the disk away from 
dust. For example, don't smoke cigarettes near the disk, because 
the smoke becomes dust that lands on the disk and wrecks the 
data.
                                         Keep the disk dry. If 
you must transport a disk during a rainstorm, put the disk in a 
plastic bag. Never drink coffee or soda near the disk: your drink 
might spill.
                                         To handle the disk, 
touch just the disk's jacket, not the brown disk itself. Holes in 
the jacket let you see the brown disk inside; don't put your 
fingers in the holes.
                                         Power surges in ancient 
computers If your computer is an IBM clone or by Apple, skip 
ahead to the next topic (``Write-protect notch'').
                                         If your computer is made 
by Commodore or Radio Shack and is so ancient that it's not an 
IBM PC clone, be careful: flipping the power switch on your 
ancient computer creates an electrical surge that wrecks the 
disk. On such a computer, don't flip the power switch when the 
drive contains a disk. Flip the power switch just when the 
drive's empty.
                                         To turn such a computer 
on, make sure the drive's empty, then flip the power switch on. 
After the power's come on, insert the disk.
                                         Before turning such a 
computer off, remove the disk from the drive. When the drive's 
empty, turn off the power.
                                         Write-protect notch When 
you buy a blank 5-inch or 8-inch floppy disk, the disk comes in 
a square black jacket. Since the jacket's square, it has four 
sides; but one of the sides has a notch cut into it.
                                         You can cover the notch, 
by sticking a plastic tab over it. The tab has a gummed back, so 
you can stick it on the disk easily and cover the notch. You get 
the tab free when you buy the disk.
                                         (For a 3-inch disk, the 
notch is different: it's a square hole near the jacket's corner 
but not on the jacket's edge. To cover it, you use a black slider 
instead of a tab. On old Apple Mac disks, the slider was red 
instead of black.)
                                         Whenever you ask the 
computer to change the info on the disk, the drive checks whether 
you've covered the notch.
                                         For a 5-inch disk, the 
normal situation is for the notch to be uncovered. For a 3-inch 
or 8-inch disk, the normal situation is for the notch to be 
covered.
                                         If the situation's 
normal, the computer will obey your command: it will change the 
info on the disk as you wish. But if the situation's abnormal 
(because the notch is covered when it should be uncovered, or is 
uncovered when it should be covered), the computer will REFUSE to 
change the disk's info.
                                         Suppose your disk 
contains valuable info, and you're afraid some idiot will 
accidentally erase or alter that info. To prevent such an 
accident, make the situation abnormal (by changing whether the 
notch is covered), so that the computer will refuse to change the 
disk's info. It will refuse to erase the disk; it will refuse to 
add new info to the disk; it will refuse to alter the disk; it 
will refuse to write onto the disk. The disk is protected from 
being changed; it's protected from being written on. The disk is 
write-protected (or locked).
                                         Since the tab affects 
whether the disk is write-protected, the tab is called a 
write-protect tab, and the notch is called a write-protect notch.
  When you buy a disk that already contains info, the disk 
usually comes write-protected, to protect you from accidentally 
erasing the info. So if you buy a 5-inch floppy disk that 
already contains info, it might come with a write-protect tab 
already covering the notch, to write-protect the disk.
  Instead of creating a notch and then covering it with a tab, 
some manufacturers save money by getting special disks that have 
no notch. The computer treats a notchless disk the same way as a 
disk whose notch is covered.
  Backup Even if you handle your disk very carefully, eventually 
something will go wrong, and some of the info on your disk will 
get wrecked accidentally.
  To prepare for that inevitable calamity, tell the computer to 
copy all info from the disk onto a blank disk, so that the blank 
disk becomes an exact copy of the original. Store the copy far 
away from the original: store it in another room, or ___ better 
yet ___ another building, or ___ better yet ___ another city. If 
you're working in a country that's having a war, store the copy 
in another country.
  The copy is called a backup. Use the backup disk when the 
original disk gets wrecked.
  Making a backup disk is like buying an insurance policy: it 
protects you against disasters.
  Every evening, make backup copies of all your disks ___ except 
for disks containing the same info as the day before.
  Each week, I get phone calls from distressed business 
executives whose disks got wrecked and who didn't make backups. 
All I can offer them is sympathy. Their companies are ruined. 
Remember: ``a backup a day keeps disaster away!''
  When you buy a floppy that already contains software, try 
copying the floppy before you begin using it. If you're lucky, 
the computer will make the backup copy without any hassles. If 
you're unlucky, the software company has put instructions on the 
floppy that make the computer refuse to copy the disk, because 
the company fears that you'll illegally give copies to all your 
friends for free. A floppy that the computer refuses to copy, and 
which is therefore protected against illegal copying, is called 
copy-protected. A floppy that you can copy is called copyable (or 
unprotected).
  Short files The information on the disk is divided into files. 
Each file has its own name and its own purpose. For example, one 
file might be named JILL and consist of a memo that you wrote to 
your friend Jill; another file might be named PAYROLL and consist 
of information about your company's payroll. Each file consists 
of many sectors.
  If one of the disk's sectors gets damaged, the computer might 
get so confused that it handles the entire file incorrectly, and 
so the entire file becomes unusable.
  To minimize such damage, avoid creating large files; create 
many small files instead. For example, if you're writing a book 
and want to store the book on your disk, do not make the entire 
book be a single file; instead, split the book into chapters, and 
make each chapter a separate file. That way, a damaged sector 
will hurt at most one chapter, and can't hurt the entire book.
  Drive cleaners Don't bother trying to clean the heads of your 
floppy drive. The heads don't collect much dirt anyway, since the 
floppy disk's jacket has a cloth liner that traps most dirt. If 
your disk ever starts to act unreliable, clean the heads if you 
wish, but the culprit is more likely a misaligned head, a 
brownout, overheating, defective software, or a mistyped command.

             HARD DISKS
                                         Hard disks are better 
than floppy disks in three ways. . . . 
Hard disks are sturdier than floppies.
Hard disks are hard and firm; they don't flop or jiggle.
They're more reliable than floppies.

Hard drives hold more information than floppy drives.
The typical floppy drive holds 360K, 720K, 1.2M, or 1.44M.
The typical hard drive holds 250M, 340M, or 420M.

Hard drives work faster than floppies.
The typical floppy disk rotates between 5 and 10 times per 
second.
The typical hard disk rotates between 60 and 120 times per 
second.
                                         Hard drives are more 
expensive than floppy drives. The typical floppy drive costs 
about $50; the typical hard drive costs about $300.
                                         Unfortunately, the 
typical hard disk can't be removed from its drive: the hard disk 
is non-removable, stuck inside its drive permanently. (Hard disks 
that are removable are rare.)
                                         Since the typical hard 
disk is stuck forever inside its drive, in one fixed place, it's 
called a fixed disk.
                                         Though the typical 
floppy-disk drive holds just one disk at a time, the typical 
hard-disk drive holds a whole stack of disks and handles all the 
stack's disks simultaneously, by using many arms and read-write 
heads. For example, the typical 420M hard drive holds a 
non-removable stack of disks, and the entire stack totals 420M. 
Each disk in the stack is called a platter.
                                         If your hard drive is 
the rare kind that holds a removable stack of disks, the stack 
comes in a cartridge or pack that you can remove from the hard 
drive.
                                         Back in 1977, the 
typical hard disk had a 14-inch diameter and was removable. The 
hard-disk drive was a big cabinet, the size of a top-loading 
washing machine; it cost about $30,000 and held 100M. It required 
a minicomputer or mainframe.
                                         Hard disks, drives, and 
prices have all shrunk since then! Now the typical hard disk has 
a diameter of just 3 inches. The typical hard drive is just 1 
inch tall, costs $279, and holds 420M. It fits in a desktop 
microcomputer.
                                         Some notebook computers 
use tiny hard disks whose diameter is just 2 inches.

                                                 IBM drive letters
                                         The typical 
IBM-compatible computer has both a floppy drive and a hard drive. 
The floppy drive is called drive A; the hard drive is called 
drive C.
                                         If the computer has two 
floppy drives, the main floppy drive is called drive A, and the 
other floppy drive is called drive B. If the computer has two 
hard drives, the main hard drive is called drive C, and the other 
hard drive is called drive D.

                                          Copy from floppy to hard & back
                                         When you buy a program, 
it usually comes on a floppy disk. To use the program, put that 
floppy disk into the floppy drive, then copy the program from the 
floppy disk to the hard disk. (To copy the program onto an 
IBM-compatible hard disk, type the word ``copy'' or ``install'' 
or ``setup''. To find out which of those three words to type and 
when, follow the instructions in the manual that came with the 
program.)
                                         Then use just the copy 
on the hard disk (which is sturdier, holds more info, and works 
faster than the floppy disk).
                                         Like floppy disks, hard 
disks are coated with magnetized iron. Floppy disks and hard 
disks are both called magnetic
disks. Like floppy disks, hard disks are in constant danger of 
losing their magnetic signals ___ and your data!
  Protect yourself! Every day, take any new info that's on your 
hard disk and copy it onto a pile of floppy disks, so that those 
floppy disks contain a backup copy of what was new on your hard 
disk.
  To avoid giant disasters, avoid creating giant files. If you're 
writing a book and want to store it on your hard disk, split the 
book into chapters, and make each chapter a separate file, so 
that if you accidentally say ``delete'' you'll lose just one 
chapter instead of your entire masterpiece.

         How the head works
  In a floppy drive, the read-write head (the ``needle'') touches 
the spinning floppy disk. But in a hard drive, the read-write 
head does not touch the spinning hard disk; instead, it hovers 
over the disk.
  The distance from the read-write head to the hard disk is a 
tiny fraction of an inch, and small enough so that the read-write 
head can detect the disk's magnetism and alter it.
  Since the head doesn't actually touch the disk, there isn't any 
friction, and so the head and the disk don't suffer from any 
wear-and-tear. That's why a hard-disk system lasts longer than a 
floppy-disk system and is more reliable.
  Winchester drives In all modern hard drives, the head acts as a 
miniature airplane: it flies above the disk. It flies at a very 
low altitude: a tiny fraction of an inch. The only thing keeping 
the head off the rotating disk is a tiny cushion of air ___ a 
breeze caused by the disk's motion.
  When you unplug the drive, the disk stops rotating, so the 
breeze stops, and the head comes to rest on a landing strip, 
which is like a miniature airport.
  Such a drive is called a flying-head drive. It's also called a 
Winchester drive, because ``Winchester'' was IBM's secret 
code-name for that technology when IBM was inventing it.
  The head flies at an altitude that's extremely low ___ about a 
ten-thousandth of an inch! That's even smaller than the width of 
a particle of dust or cigarette smoke! So if any dust or smoke 
lands onto the disk, the head will smash against it, and you'll 
have a major disaster.
  To prevent such a disaster, the entire Winchester drive is 
sealed air-tight, to prevent any dust or smoke from entering the 
drive and getting onto the disk. Since the drive is sealed, you 
can't remove the disks (unless you buy an extremely expensive 
Winchester drive that has a flexible seal).

                Speed
  Here's how the computer retrieves data from the drive.
  First, the drive's head moves to the correct track. The time 
that the head spends moving is called the seek time. Since that 
time depends on how far the head is from the correct track, it 
depends on where the correct track is and where the head is 
moving from.
  According to calculus, on the average the head must move across 
a third of the tracks to reach the correct track. The time to 
traverse a third of the tracks is therefore called the average 
seek time.
  A millisecond (ms) is a thousandth of a second. In a typical 
hard drive, the average seek time is 12 milliseconds. (In faster 
hard drives, the average seek time is 9 milliseconds; in slower 
hard drives, the average seek time is 28 milliseconds.)
  After the head reaches the correct track, it must wait for the 
drive to rotate, until the correct sector reaches the head.
That rotation time is called the latency. On the average, the 
head must wait for half a revolution; so the average latency time 
is a half-revolution. The typical hard drive rotates 60 times per 
second, so a half-revolution takes half of a sixtieth of a 
second, so it's a 120th of a second, so it's about .008 seconds, 
which is 8 milliseconds.
                                         If you add the average 
seek time to the average latency time, you get the total average 
access time. So for a typical hard drive, the average access time 
= 12 milliseconds seek + 8 milliseconds latency = 20 
milliseconds.
                                         During the last few 
years, hard drive manufacturers have become dishonest: they say 
the ``average access time'' is 12 milliseconds, when they should 
actually say the ``average seek time'' is 12 milliseconds.
                                         After the head finally 
reaches the correct sector, you must wait for the head to read 
the data. If the data consumes several sectors, you must wait for 
the head to read all those sectors.

                                                   Manufacturers
                                         Most hard drives for 
microcomputers are manufactured by four companies: Seagate 
Technology (ST), Conner Peripherals, Quantum, and Western 
Digital.
                                         Seagate was the first of 
those companies to make hard drives for microcomputers, and it 
set the standard that the other companies had to follow. New 
Seagate drives work fine, though Seagate's older models were 
often noisy and unreliable.
                                         Conner was the first 
company to invent hard drives tiny enough to fit in a laptop or 
notebook computer. Seagate ignored the laptop/notebook 
marketplace too long, and Conner's popularity zoomed up rapidly. 
Conner became the fastest-growing company in the history of 
American industry, though Conner's popular finally started to 
level off.
                                         Quantex became famous by 
manufacturing the hard drives that Apple buys to put in Mac 
computers. Quantex also builds drives for IBM PC clines. Quantex 
drives are excellent.
                                         Western Digital has 
invented hard drives that cost less. They're popular in cheap 
clones and discount computer stores.
                                         When buying a hard 
drive, you might also need to buy a hard-drive controller.

                                                 How many sectors?
                                         Back in the 1980's, the 
typical hard-drive controller for IBM-compatible computers put 17 
sectors on each track. That scheme was called the Seagate 
Technology 506 with Modified Frequency Modulation (ST506 MFM).
                                         An improved scheme, 
which squeezed 26 sectors onto each track, was called the ST506 
with Run Length Limited (ST506 RLL). A further improvement, which 
squeezed 34 sectors onto each track, was called the Enhanced 
Small Device Interface (ESDI).
                                         Squeezing extra sectors 
onto each track increases the drive's capacity (total number of 
megabytes) and also the transfer rate (the number of sectors that 
the head reads per rotation or per second).
                                         All those schemes ___ 
MFM, RLL, and ESDI ___ have become obsolete.
                                         Now the most popular 
scheme is called Integrated Drive Electronics (IDE). Like ESDI, 
it squeezes 34 sectors onto each track; but it uses special 
tricks to transfer data faster. It's used on all popular 
IBM-compatible hard drives under 600M. It's starting to become 
popular in the 600M-1100M range also.
  An even faster scheme is the Small Computer System Interface 
(or SCSI, which is pronounced ``scuzzy''). It's used on all Mac 
hard drives. It's also used on most IBM-compatible hard drives 
over 600M.

               Discounts on drives
  You can buy a hard drive cheaply from a discount dealer called 
Hard Drives International (HDI). It's a division of Insight, 
which is at 1912 W. Fourth St., Tempe AZ 85281; phone 
800-998-8028 or 602-902-1176. You get a 30-day money-back 
guarantee and toll-free technical help. You can call sales and 
technical support anytime (24 hours per day, 365 days per year).
  A smaller dealer, Mega Haus, usually charges even less. But 
Mega Haus doesn't have a true 30-day money-back guarantee (you 
must pay a 15% restocking fee), doesn't stay open late at night, 
and doesn't ship outside the USA. Mega Haus is in Houston at 
800-786-1153 (IBM), 800-786-1173 (Mac), or 713-333-1910.
  IBM-compatible drives For an IBM-compatible hard drive, 
discount dealers such as HDI charge about 50 cents per megabyte, 
plus $75. So here's how to estimate a hard drive's price.
Take the number of megabytes, divide by 2, then add 75. That's 
the price in dollars.
  For example, here's how to find the price of a 540-megabyte 
hard drive.
Take 540, divide by 2 (giving 270), then add 75. That makes 345, 
so the drive's price is $345.
  That formula (price = megabytes/2 + 75) is just an 
approximation. The exact price depends on the dealer, the drive's 
speed, and which models are on sale this month.
  Besides buying the hard drive, you must also buy a card to put 
in the computer's slot. For example, here are HDI's prices:
CapacitySeek timeTypeBrand  Model numberHDI's price
 340M   12 ms   IDE Western DigitalWD2    340 A $229 +  $20 card
 420M   12 ms   IDE Western DigitalWD2    420 A $279 +  $20 card
 540M   12 ms   IDE Western DigitalWD2    540 A $349 +  $20 card
 730M   12 ms   IDE Western DigitalWD2    700 A $469 +  $20 card
1080M   10 ms   IDE Western DigitalWD3   1000 A $679 +  $20 card
1800M   10 ms   SCSIQuantum QUPD  1800 S $939 + $100 card
4294M    8 ms   SCSISeagate ST1   5150 N$2399 + $100 card
9100M   10 ms   SCSIMicropolisMC19    91$4059 + $100 card
  For the IDE drives, the extra $20 is for a paddle board that 
fits in an IBM PC AT slot. For the SCSI drives, the extra $100 is 
for a hard-drive controller card that fits in an IBM PC AT slot.
  At the end of the model number, an A means AT-bus IDE; anything 
else (S, N, or blank) means SCSI.
  For Western Digital and Quantum drives, the main part of the 
model number is the capacity. For Micropolis drives, the main 
part of the model number is the capacity divided by 100. For 
Seagate drives, the main part of the model number is the 
unformatted capacity, which is about 10% bigger than the usable 
(formatted) capacity.
  Each price in that chart is close to the price predicted by the 
formula ``price=megabytes/2+75''. How close? Within 13%.
  Each price in that chart went into effect in July 1994. By the 
time you read this book, prices might be even lower! Prices 
continually drop.
  Mac drives The price of a Mac hard drive depends on whether the 
drive is internal (fits inside the Mac) or external (comes in a 
separate box that you put next to the Mac). Internal drives are 
cheaper; but if your Mac is small or filled up, you must buy an 
external drive instead.
  For Mac drives, Mega Haus charges much less than HDI. Here are 
the Mega Haus prices:
CapacitySeek timeRotationCacheBrandInternalExternal
 170M   17 ms   3600 rpm  32KQuantum $179  $239
 270M   12 ms   4500 rpm 128KQuantum $238  $298
 340M   12 ms   4500 rpm 128KQuantum $275  $335
 540M   12 ms   4500 rpm 128KQuantum $389  $449
1080M   10 ms   5400 rpm 512KQuantum $725  $785
1750M   10 ms   5400 rpm 256KMicropolis $999$1059
2148M    9 ms   5400 rpm 512KSeagate$1429 $1529
3020M   11 ms   5400 rpm 256KMicropolis$2139$2169

                                                     What size 
hard drive to buy Back in the 1980's, a 40-megabyte drive was 
considered ``big''. In the 1990's, a 40-megabyte drive is 
considered ``too small''. Here's why.
                                                     MS-DOS 6.2 
consumes over 5 megabytes. Windows 3.1 consumes over 10 
megabytes. So far, we've consumed over 15 megabytes!
                                                     The typical 
Windows word-processing program (such as such Word Perfect 6 or 
Microsoft Word 6) consumes about 25 megabytes. So altogether, for 
DOS plus Windows plus a word-processing program, we've consumed 
over 40 megabytes already!
                                                     You'll need 
additional megabytes for additional business programs (about 10 
megabytes per program), plus additional megabytes to hold what 
you type.
                                                     After buying 
the computer, you'll probably spend the next several years 
accumulating many programs (a few each year). After a year or 
two, you'll accumulate over 170 megabytes, and you'll wish you'd 
bought a bigger drive instead.
                                                     Buy at least 
a 340-megabyte drive. A 340-megabyte drive costs just slightly 
more than a 170M drive and will last you for many years. You're 
buying peace of mind!
                                                     It's much 
cheaper to buy a 340-megabyte drive now than to buy a 
170-megabyte drive now and another 170-megabyte drives later. 
Another reason for buying a 420-megabyte drive is that it will 
act faster than a 170-megabyte drive.
                                                     For example, 
suppose you want to store 170 megabytes of information, and 
you're debating whether to buy a 170-megabyte drive or a 
340-megabyte drive. Suppose each drive is advertised as having a 
12-millisecond seek time. The 340-megabyte drive will 
nevertheless act faster. Here's why. . . . 
                                                     Suppose you 
buy the 340-megabyte drive and use just the first 170 megabytes 
of it. Since you're using just the first half of the drive, the 
head needs to move just half as far as usual; so over the 
170-megabyte part that you're using, the effective average seek 
time is just half as much as usual: it's 6 milliseconds!

                     CD-ROMS
  Instead of buying a program on a floppy disk, you can buy a 
program on the same kind of compact disk (CD) that holds music. 
Since the CD cannot be erased, it's called a CD read-only memory 
(CD-ROM).
  To make your computer read the CD-ROM disk, put the disk into a 
CD-ROM drive, which is a souped-up version of the kind of CD 
player that plays music.
  Like an ordinary CD player, a CD-ROM drive uses just optics. No 
magnetism is involved. The drive just shines a laser beam at the 
shiny disk and notices, from the reflection, which indentations 
(pits) are on the disk; the pattern of pits is a code that 
represents the data. So a CD-ROM drive is an example of an 
optical disk drive.
  To put the disk into the drive, press a button on the drive. 
That makes the drive stick its tongue out at you! The tongue is 
called a tray. Put the disk onto the tray, so that the disk's 
label is face-up. (If the drive is old-fashioned, you must put 
the disk into a caddy first; but the most modern drives are 
caddyless.) Then push the tray back into the drive. Finally, use 
the keyboard or mouse to give a command that makes the computer 
taste what you've put on its tongue.

                IBM drive letters
  In the most modern kind of IBM-compatible computer, drive A is 
a 3-inch floppy drive (1.44M), drive B is a 5-inch floppy drive 
(1.2M), drive C is a hard drive (holding about 420M), and drive D 
is a CD-ROM drive.
  But if your computer has two hard drives, here's what happens: 
the first hard drive is C, the second hard drive is D, and the 
CD-ROM drive is E.

                      Size
  CD-ROM disks come in two sizes:
The standard size has a diameter of 12 centimeters (which is 
about 5 inches) and holds 540 megabytes.
The miniature size has a diameter of 8 centimeters (which is 
about 3 inches) and holds 180 megabytes.
  Your CD-ROM drive can handle both sizes of CD-ROM disks. Each 
CD-ROM disk is single-sided: all the data is on the disk's bottom 
side ___ the side that doesn't have a label.
  Yes, a standard-size CD-ROM disk holds 540 megabytes, which is 
a lot!
It's more than the typical hard drive.
It's 375 times as much as a high-density 1.44M floppy.
It's 1500 times as much as a 360K floppy.
  Because a CD-ROM disk holds so much, a single CD-ROM can hold a 
whole library (including encyclopedias, dictionaries, other 
reference materials, famous novels, programs, artwork, music, and 
videos). It's the ideal way to distribute massive quantities of 
information! Moreover, a CD-ROM disk costs just $1.50 to 
manufacture (once you've bought the appropriate CD-ROM-making 
equipment, which costs several thousand dollars).

                Speed
  When buying a CD-ROM drive, the most important factor to 
consider is the drive's speed.
  Transfer rate The speed at which the drive spins is called the 
transfer rate. The higher, the better!
On old drives, the transfer rate was 150 kilobytes per second.

Most new drives spin twice as fast: 300K per second.
That's called double spin or double speed or dual speed or 2X.

Some drives spin even faster: 450K per second.
That's called triple spin or triple speed or 3X.

The fastest drives spin at 600K per second.
That's called quad spin or quad speed or 4X.
  Seek time The average time it takes for the head to move to the 
correct track is called the average seek time.
  The lower the average seek time, the better!
Under 200 milliseconds is great.
  200-300 milliseconds is good.
  300-400 milliseconds is typical.
  400-500 milliseconds is poor.
 Over 500 milliseconds is terrible.

           Buying a drive
  If you're looking for an IBM-compatible drive that's reasonably 
fast at a low price, get the Sony CDU-33A or the Mitsumi FX001-D. 
Each of those drives is double-spin.
  The Sony's average seek time is 320 milliseconds. The Mitsumi's 
is better, 250 milliseconds.
  You can buy that Sony drive for $169, the Mitsumi for $139, 
from discount dealers such as USA Flex in Illinois (phone 
800-723-2261 or 708-582-6202).
  When buying those drives, make sure you get the right model! 
For the Sony, make sure you get the CDU-33A, not the CDU-31A 
(which is slower, at 490 milliseconds). For the Mitsumi, make 
sure you get the FX001-D, not the FX001 (which is single-spin 
instead of double-spin).
  Faster drives For even faster drives ___ at higher prices ___ 
consider the NEC 3Xi (triple-spin, 195 milliseconds, $424), the 
Plextor PX-34CH (quadruple-spin, 220 milliseconds, $475), or the 
NEC 4X Pro (quadruple-spin, 180 milliseconds, $929). Those NEC 
prices are from USA Flex; the Plextor's price is from Insight, a 
discount dealer in Arizona (phone 800-927-9935 or 602-902-1176).
  But if you buy one of those faster drives, you'll be 
disappointed: those drives make the typical CD-ROM program run 
just slightly faster. That's because most CD-ROM programs are 
still designed under the assumption you're using a CD-ROM drive 
that's slow. So save your money: buy just a cheap drive (the Sony 
CDU-33A or Mitsumi FX001-D).
  External drives Those prices are for internal drives, which fit 
inside the computer's system unit. If your system unit is filled 
up and doesn't have any room left to insert an internal drive, 
you must buy an external drive instead, which sits outside the 
system unit and costs about $100 more.
  Multimedia kits If you buy a CD-ROM drive, you'll also want a 
sound card, a pair of stereo speakers, and a few sample CD-ROM 
disks (so you can admire all that equipment you bought). That 
combo ___ a CD-ROM drive, sound card, pair of speakers, and 
sample CD-ROM disks ___ is called a multimedia kit.
                                         For example, USA Flex 
sells the Flex CD-Pro Classic, which is a kit including the Sony 
CDU-33A drive and the Sound Blaster 16 sound card. That kit costs 
$249; add $15 for a pair of speakers (batteries not included!), 
plus $49 for a collection of 3 sample CD-ROM disks. To pay $50 
less, get the Flex CD-Pro Value instead, which is similar but 
includes imitations of the Sony and Sound Blaster.
                                         Insight sells the Reveal 
Multimedia FX. It's a multimedia kit that includes the Reveal 
CD-ROM drive (double-spin, 320 milliseconds, internal), sound 
card, pair of speakers, headset (including a microphone), and 
sample disks. . . . 
The model 01, at $299, includes 5 sample disks.

The model 02, at $349, includes 16 sample disks and a second 
microphone (which stands on your desk).

The model 04, at $479, includes 23 sample disks and a second 
microphone.

The model 08, at $599, includes 35 sample disks, second 
microphone, higher-quality speakers, higher-quality sound card, 
and higher-quality headset.
                                         When you buy a new 
computer, you can ask the salesperson to include a multimedia 
kit. The computer, together with the multimedia kit, form a combo 
that's called a multimedia computer system. For example, Quantex 
sells multimedia systems based on the Sony CDU-33A drive; VTech 
sells multimedia computer systems based on the Mitsumi FX001-D 
drive.

                                                       Dirt
                                         A CD-ROM disk's main 
enemy is dirt.
                                         When you buy a CD-ROM 
disk, it comes in a clear square box, called the jewel box. To 
use the CD-ROM disk, remove it from the jewel box and put the 
disk into the drive. When you finish using the disk, put it back 
into the jewel box, which keeps the dust off the disk.
                                         When putting the CD-ROM 
disk into or out of a drive, don't put your fingers on the disk's 
surface: instead, hold the disk by its edge, so your greasy 
fingerprints don't get on the disk's surface.
                                         Once a month, gently 
wipe any dust off the CD-ROM disk's bottom surface (where the 
data is). While wiping, be gentle and don't get your greasy 
fingerprints on the disk. Start in the middle and wipe toward the 
outer edge.
                                         For example, my 
assistant and I were getting lots of error messages when using a 
sample CD-ROM disk we bought from Microsoft. I was going to phone 
Microsoft to complain, but my assistant asked, ``What about 
dust?'' I flipped the CD-ROM disk over and sure enough, a big 
ball of dust was on the disk's bottom side, where the data is 
recorded. I wiped it off. That CD-ROM disk has worked perfectly 
ever since.
                                         I was so embarrassed! If 
my assistant hadn't reminded me to wipe the dust off, I'd have 
wasted hours of Microsoft's time hunting uselessly for a 
high-tech reason my CD-ROM disk wasn't working.

                                                   Other dangers
                                         Don't put any fluids on 
the disk. The fluids that clean phonograph records will wreck 
CD-ROM disks.
                                         If you want to write on 
the disk, use a felt-tipped pen (not a ballpoint or pencil). 
Don't stick any labels on the disk.