Here's part of "The Secret Guide to Computers," copyright by Russ Walter, 27th edition. For newer info, read the 30th edition at www.SecretFun.com.

 


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 (under 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 standard sizes

Floppy disks come in three standard sizes:

The most popular size is called a 3½-inch floppy disk, because it comes in a square jacket that’s about 3½ inches on each side. (Actually, each side of the jacket is slightly more than 3½ inches, and the disk’s diameter is slightly less.)

An older size, used mainly on older computers, is called 5¼-inch. It comes in square jacket that’s exactly 5¼ 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 5¼-inch floppy disk is called a minifloppy.

A 3½-inch floppy disk is called a microfloppy.

Here’s their history:

8-inch floppies were invented in the early 1970’s by IBM.

5¼-inch floppies were invented in the late 1970’s by Shugart Associates, which later became part of Xerox.

3½-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!

Jacket colors

The jacket of a 5¼-inch or 8-inch floppy disk is usually black. The jacket of a 3½-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.

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 3½-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 3½-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 info onto the disk:

By using the computer’s keyboard or mouse, command the computer to use the disk. Then type the info you want to transfer to the disk.

To transfer the info 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 info 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 3½-inch high-density floppy drive. Here’s how it works:

It holds a 3½-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, ½K.

Since the disk has 2 sides, 80 tracks per side, 18 sectors per track, and ½K per sector, the disk’s total capacity is “2 times 80 times 18 times ½K”, 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 3½-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 3½-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 (½K) for bureaucratic overhead. An IBM-compatible computer uses 33 sectors (16½K) for bureaucratic overhead, leaving just 1423½K (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 3½-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 3½-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 3½-inch disk has an extra square hole cut through its jacket.

Old computers use inferior floppy drives, whose capacities are below 1.44M.

A capacity below 150K                        is called single-density (SD).

A capacity above 150M but below 1M is called double-density (DD).

A capacity above 1M                              is called high-density (HD).

Anything below high-density is called low-density.

Although the jacket of a high-density 3½-inch disk has “HD” stamped on it 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 name     Capacity                         Details

5¼-inch double-density   360K                             40 tracks per side,   9 sectors per track

5¼-inch high-density    1200K (which is 1.2M)    80 tracks per side, 15 sectors per track

3½-inch double-density   720K                             80 tracks per side,   9 sectors per track

3½-inch high-density    1440K (which is 1.44M)  80 tracks per side, 18 sectors per track

Each of those IBM-compatible drives is double-sided and has ½K per sector. They’re manufactured by companies such as NEC, Teac, Chinon, Epson, and Alps. The fanciest drives (3½-inch high-density) used to be expensive, but now you can buy them for just $29 from mail-order discount dealers (such as USA Flex at 444 Scott Dr., Bloomingdale IL 60108, phone 800-723-2261 or 708-582-6206).

Mac drives For Mac computers, three kinds of floppy drives have been popular:

Mac drive’s name    Capacity                         Details

1-sided double-density     400K                             1 side,       8-12 sectors per track

2-sided double-density     800K                             2 sides,  8-12 sectors per track

high-density                  1440K (which is 1.44M)  2 sides,  18 sectors per track

Each Mac drive is 3½-inch and has 80 tracks per side, ½K 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.

Ancient computers For ancient computers, many kinds of floppy drives were invented:

Computer                  Drive capacity     Details

Apple 2 family                 140K                     5¼", 1 side,  35 tracks, 16 sectors, ¼K per sector

Tandy Color Computer 157½K                   5¼", 1 side,  35 tracks, 18 sectors, ¼K per sector

Tandy Models 3, 4, 4P  180K                     5¼", 1 side,  40 tracks, 18 sectors, ¼K per sector

Tandy Model 4D           360K                     5¼", 2 sides, 40 tracks, 18 sectors, ¼K per sector

Commodore 64             170¾K                   5¼", 1 side,  35 tracks, 17-21 sectors, ¼K per sector

Commodore Amiga          880K                     3½", 2 sides, 80 tracks, 11 sectors, ½K 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 5¼-inch disks revolve 5 times per second. That makes 300 revolutions per minute, 300 rpm.

8-inch disks and high-density 5¼-inch disks revolve faster: 6 times per second (360 rpm).

3½-inch disks revolve even faster: between 6½ 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 3½-inch disk will not work in a 5¼-inch drive.

If you buy a blank 3½-inch floppy disk, you can stick it into any normal 3½-inch drive, regardless of who manufactured the drive and who manufactured the computer. But after you’ve put info onto the disk, that info is understandable only to your kind of computer. For example, an Apple 2c 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 info understandable to your computer.

If your drive is single-density or double-density, it cannot handle high-density disks at all.

Here are peculiarities about 5¼-inch drives and disks:

If your drive is 5¼-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 5¼-inch high-density drive to write on, avoid buying single-density or double-density disks.

The three crummy kinds of 5¼-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 yourself (by typing a command on your computer’s keyboard or by using the mouse).

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                            100disks    1000

5¼-in. double-density, unformatted   $19+$1.20 $160+$12

5¼-in. high-density, unformatted      $26+$1.20 $210+$12

3½-in. high-density, formatted          $28+$2.40 $250+$24

Add up the prices of what you want, then add the handling charge ($3.25). For example, for 100 of the best disks (3½-inch high-density, formatted), MEI charges you $28 (for the disks) + $2.40 (shipping) + $3.25 (handling), which is $33.65. That’s about 34¢ per disk. For 1000 of the best disks, MEI charges you $250 + $24 + $3.25, which is $277.25, which comes to about 28¢ 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 info costs much more. The price depends on how valuable the info is. A disk that explains to the computer how to play a game costs about $25. A disk teaching the computer how to handle a general business task (such as accounting, filing, or correspondence) usually costs about $100.

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 6 inches away from paper clips, stereos, TV’s, phones, 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.

3½-inch floppy disks come in strong jackets, but 5¼-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’s 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 5¼-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 3½-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 5¼-inch disk, the normal situation is for the notch to be uncovered. For a 3½-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 5¼-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.

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.

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).

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.

Super-capacity floppies

A standard floppy disk holds up to 1.44M. Super-capacity floppy disks can hold even more.

Zip The most popular super-capacity floppy disk is the Zip disk. Slightly bigger than a 3½-inch floppy disk, it’s 4-inch. It holds 100M, which is 70 times as much as a 1.44M floppy!

Zip disks cost $13 each if you buy 2, $12 each if you buy 6, $11 each if you buy 10, $10 each if you buy 20.

To use Zip disks, you must buy a Zip drive. It reads just Zip disks and costs $89. (That price includes one blank Zip disk.)

The Zip drive is made by Iomega. Zip disks are available from many manufacturers, such as Iomega and Sony. You can buy Zip drives and disks at your local computer store.

Zip 250 You can buy a Zip 250 disk, which resembles a Zip disk but holds 250M instead of 100M. Zip 250 disks cost $18 for 1, $17 each if you buy 4. To use them, you must buy a Zip 250 drive, which can also handle traditional Zip disks and costs $187.

LS-120 A pleasant alternative is the laser servo 120M disk (LS-120 disk). Like a 1.44M disk, an LS-120 disk is 3½-inch, but it holds more (120M).

LS-120 disks cost $14 each if you buy 3, $12 each if you buy 5, $10 each if you buy 10. LS-120 disks made by Imation are called SuperDisks.

To use LS-120 disks, you must buy an LS-120 drive. It reads LS-120 disks and 1.44M disks. It costs $100. It’s faster than a Zip drive. You can buy LS-120 drives made by Imation and O.R. Technology.

PD The final step up is the Panasonic disk (PD). It’s 5-inch and holds 650M. It costs $34, but you can pay just $30 each by getting 10 at a time.

To use PD disks, you must buy a PD drive. It reads PD disks and CD-ROM disks. It costs $349. You can buy PD drives made by Panasonic, Toray, and Micro Solutions.


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 1.44 megabytes.

The typical hard drive holds 20 gigabytes (which is about 20,000 megabytes).

Hard drives work faster than floppies.

The typical floppy disk rotates between 5 and 10 times per second.

The typical hard disk rotates between 90 and 167 times per second.

Hard drives cost more than floppy drives. The typical floppy drive costs $29; the typical hard drive costs about $240.

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, a 20-gigabyte hard drive holds a non-removable stack of disks, and the entire stack totals 20 gigabytes. 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 100 megabytes. 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 3½ inches. The typical hard drive is just 1 inch tall, costs about $160, and holds 20,000 megabytes. It fits in a desktop microcomputer.

Some notebook computers use tiny hard disks whose diameter is just 2½ 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; the other floppy drive is called drive B.

If the computer has two hard drives,

the main hard drive is called drive C; 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 or a CD-ROM disk. If it comes on a floppy disk, 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” or use your mouse. To find out which to do 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 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 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, so the head and the disk don’t suffer from any wear-and-tear. A hard-disk system therefore 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 airtight, 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. That’s why the time to traverse a third of the tracks is called the average seek time.

A millisecond (ms) is a thousandth of a second. In a typical hard drive, the average seek time is 10 milliseconds. (In the fastest hard drives, the average seek time is 7½ milliseconds; in the slowest hard drives made today, the average seek time is 14 milliseconds; in older hard drives that are no longer made, the average seek time was 28 milliseconds.)

After the head reaches the correct track, it must wait for the disk 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 90 times per second, so a half-revolution takes half of a 90th of a second, so it’s a 180th of a second, so it’s about .006 seconds, which is 6 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 = 10 milliseconds seek + 6 milliseconds latency = 16 milliseconds.

During the last few years, hard drive manufacturers have become dishonest: they say the “average access time” is 10 milliseconds, when they should actually say the “average seek time” is 10 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 three American companies: Seagate Technology (ST), 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.

Quantum became famous by manufacturing the hard drives that Apple buys to put in Mac computers. Quantum also builds drives for IBM PC clones. Quantum drives are excellent.

Western Digital has invented hard drives that cost less. They’re popular in cheap clones and discount computer stores.

Conner was the first company to invent hard drives tiny enough to fit in a laptop or notebook computer.

Seagate ignored the laptop/notebook market too long, and Conner’s popularity zoomed up fast. Conner became the fastest-growing company in the history of American industry! But then Conner’s competitors caught up and Conner’s popularity sunk back down. In Febuary 1996, Seagate bought Conner.

Other popular manufacturers of hard drives are America’s Maxtor & Micropolis, Japan’s NEC & Fujitsu, and Korea’s Samsung.

When buying a hard drive, you might also need to buy a hard-drive controller.

How many sectors?

How many sectors do you get on a track?

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.

The original version of IDE was limited to small drives: up to 528M.

A new, improved version, called Enhanced IDE (EIDE), can handle bigger drives. It also goes faster: it transfers 16.6 megabytes per second. Enhanced IDE was invented by Western Digital and is also used by Conner and Maxtor. Seagate invented competing methods (called Fast ATA-2 and Fast ATA-3), which also transfer 16.6 megabytes per second; they’re used by Seagate, Quantum, Fujitsu, and Samsung.

Those technologies (Enhanced IDE, Fast ATA-2, and Fast ATA-3) have all being replaced by Ultra, which transfers twice as fast: 33.3 megabytes per second! The Ultra version of EIDE is called Ultra IDE; the Ultra version of Fast ATA is called Ultra ATA.

An extra-fast Ultra ATA has been invented. Called Ultra ATA-66, it transfers 66.6 megeabytes per second instead of 33.3. You can buy Ultra ATA-66 drives holding up to 76.8 gigabytes.

A totally different fast scheme is the Small Computer System Interface (or SCSI, which is pronounced “scuzzy”).

The newest, fastest version of SCSI, called Ultra 160 SCSI, transfers 160 megabytes per second.

During the 1980’s and early 1990’s, SCSI was used on most Mac hard drives and the biggest IBM-compatible hard drives, because IDE drives were too slow and held just a few megabytes. But during the late 1990’s, IDE drives became dramatically faster, bigger and cheaper, so SCSI drives have become unpopular.

Discounts on drives

You can buy hard drives cheaply from these discount dealers:

Dirt Cheap Drives

usually lowest prices; ships just to USA

open weekdays 8AM-8PM, Saturday 9AM-3PM, Central Time

3716 Timber Drive, Dickinson TX 77539

phone 800-473-0960 or 281-534-4140

Megahaus

low prices; ships to USA & Canada

open weekdays 8AM-8PM, Saturday 9AM-3PM, Central Time

2201 Pine Drive, Dickinson TX 77539

phone 800-786-1185 or 281-534-3919

Insight (and its division called Hard Drives International)

slightly higher prices; ships to all countries

open always (every day & night, round-the-clock, 24 hours)

1912 W. Fourth St., Tempe AZ 85281

phone 800-INSIGHT or 602-902-1176

IBM-compatible drives Modern, popular IBM-compatible hard drives are Ultra ATA (or Ultra ATA-66), hold 20 or 30 gigabytes, and cost about $5 per gigabyte, so:

A 20-gigabyte drive costs about $100.

A 30-gigabyte drive costs about $150.

Besides buying the hard drive, you must also buy a card to put in the computer’s slot (unless your computer contains such a card already). For example, here are the prices charged by Dirt Cheap Drives for Ultra ATA (and Ultra ATA-2) drives:

Capacity     Rotation  Cache  Brand                Model number      Price

10.2 G          5400 rpm ½ M       Seagate               ST3          10212   A      $79

15.3 G          5400 rpm ½ M       Maxtor               M3        1536  U2    $85

20.4 G          5400 rpm ½ M       Seagate               ST3          20423   A      $89

30.7 G          5400 rpm ½ M       Maxtor               M3        3073  U4  $129

30.7 G          7200 rpm 2 M       IBM                    07N          3929         $179

40    G          7200 rpm 2 M       Maxtor               M5        4098  U8  $235

46.1 G          7200 rpm 2 M       IBM                    07N          3931         $269

61.4 G          7200 rpm 2 M       IBM                    07N          3933         $454

76.8 G          7200 rpm 2 M       IBM                    07N          3935         $555

In that chart, “G” means “gigabytes”. (When discussing hard drives, a “gigabyte” is defined to mean “1000 megabytes”.)

For Western Digital drives, the model number is 10 times the number of gigs.

For Maxtor drives, the model number’s main part is 100 times the number of gigs.

For Quantum drives, the model number is 1000 times the number of gigs.

For Seagate drives, the model number’s main part is 1000 times the number of gigs.

A cable runs from the drive to a card, which fits into an IBM AT slot. The card costs extra:

For Ultra ATA-66 drives, get an Ultra ATA-66 controller card, which costs $35. For Ultra 160 SCSI drives, get an Ultra 160 SCSI controller card instead, which costs $159.

The drive’s cache (or buffer) is RAM chips holding copies of the sectors you used recently — so if you want to look at those sectors again, you can read from the RAM chips (which are fast) instead of waiting for the disk to spin (which is slow).

Those were the prices when this book went to press in September 2000. By the time you read this book, prices might be even lower.

During the last 10 years, hard-drive prices have dropped — and hard-drive capacities have grown — dramatically! Here’s what size hard drive you could get for about $100, $200, $300, and $1000 each year:

Year  $100                 $200                      $300                    $1000       .

1991                       .04 G (=   40 M)        .08 G (=   80 M)      .34 G (= 340 M)

1992                       .05 G (=   50 M)        .09 G (=   90 M)      .34 G (= 340 M)

1993                       .13 G (= 130 M)        .25 G (= 250 M)    1.0   G

1994                       .34 G (= 340 M)        .42 G (= 420 M)    1.8   G

1995                       .85 G (= 850 M)      1.2   G                     4.2   G

1996                     1.2   G                       2.1   G                     4.2   G

1997    1.2 G        3.5   G                       5.2   G                     9.0   G

1998    2.5 G        8.6   G                     12.7   G

1999    6.4 G      13.0   G                     20.4   G

2000  20.4 G      30.7   G                     46.1   G


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 an external 20.4-gigabyte hard drive that attaches to the iMac’s USB port, Megahaus charges $195.

Buy a big drive Back in the 1980’s, a 40-megabyte drive was considered “big”, and it was the most popular size to buy. In the 1990’s, a 40-megabyte drive is considered too small, because the major programs consume about 40 megabytes each. Ten major programs consume a total of about 400 megabytes — plus about 40 megabytes more for Windows itself.

Buy at least a 10-gigabyte drive. A 10-gigabyte drive costs just slightly more than a 5-gigabyte drive and will last you for many years. You’re buying peace of mind!

It’s much cheaper to buy a 10-gigabyte-megabyte drive now than to buy a 5-gigabyte-megabyte drive now and another 5-gigabyte-megabyte drive later.

Another reason for buying a 10-gigabyte drive is that it will act faster than a 5-gigabyte drive.

For example, suppose you want to store 5 gigabytes of info, and you’re debating whether to buy a 5-gigabyte drive or an 10-gigabyte drive. Suppose each drive is advertised as having a 10-millisecond seek time. The 10-gigabyte drive will nevertheless act faster. Here’s why.…

Suppose you buy the 10-gigabyte drive and use just the first 5 gigabytes 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 5-gigabyte part that you’re using, the effective average seek time is just half as much as usual: it’s 5 milliseconds!

Removable hard disks Instead of buying a super-capacity floppy drive (such as a Zip drive, Zip 250 drive, LS-120 drive, or PD drive), consider buying a hard drive called the Orb, manufactured by Castlewood. It costs $175 and includes a 2.2-gigabyte hard disk that’s removable. You can buy extra 2.2-gigabyte hard disks for just $29 each. Such a hard disk holds much more than a super-capacity floppy disk; it’s a better deal. Get those prices from discount dealers such as Dirt Cheap Drives.

RAID

If you need more than 25 gigabytes, attach several hard drives together, and make the drives all act simultaneously. The group of drives is called a drive array and acts as one huge drive. That technique is called RAID (which originally stood for Redundant Array of Inexpensive Disks but now stands for Redundant Array of Independent Disks).

Here are the most popular versions of RAID:

RAID level 0, called data striping, is the fastest. It divides each long file into several stripes. A stripe’s first part is put onto drive 1, second part onto drive 2, third part onto drive 3, etc., simultaneously, so that the stripe spans across all the drives. Each drive therefore has to handle just part of each stripe and just part of each file and finishes faster.

RAID level 1, called data mirroring, is the safest. It uses just two drives. It puts each file onto drive 1 and simultaneously puts a backup copy of the file onto drive 2, so that drive 2 always contains an exact copy of what’s on drive 1. That way, if drive 1 ever fails, the computer can get the info from drive 2.

RAID level 3, called shared data parity, is more sophisticated: it’s a clever compromise between RAID level 0 and RAID level 1. Like RAID level 0, it divides each long file into stripes, puts a stripe’s first part onto drive 1, second part onto drive 2, third part onto drive 3, etc.; but onto the final drive it puts parity info instead, which is info that the computer uses to double-check the accuracy of the other drives.

RAID level 5, called distributed data parity, is the most sophisticated. It resembles RAID level 3; but instead of putting all the parity info onto the last disk, it puts the first stripe’s parity info onto the first disk, the second stripe’s parity info onto the second disk, etc., so that the parity info is distributed among all the disks, to prevent the last disk from getting overworked and bogging down the whole system.


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.

A CD that holds music is called a music CD (or audio CD).

A CD that holds computer data instead is called a computer CD (or data CD). Since the computer data on it cannot be erased, a computer-data CD is also 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

Here’s how a modern IBM-compatible computer assigns the drives:

Drive A is a 3½-inch floppy drive (1.44M).

Drive B is a 5¼-inch floppy drive (1.2M).

Drive C is a hard drive (about 4G).

Drive D is typically 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 the next letter (E).

If you bought just one hard drive but plan to buy a second hard drive later, you can leave “drive D” empty and make the CD-ROM drive be 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 650 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.

On a standard-size CD-ROM disk, there are 2 billion pits. They’re all arranged into a single spiral (like the groove on a phonograph record). If you were to unravel the spiral, to make it a straight line, it would be 3 miles long!

On a CD, each “song” is called a track; it can hold music or computer data. Each “song” (track) can be as long or as short as you wish.

The standard-size CD can hold 99 tracks, totaling an hour of music (for an audio CD) or 650 megabytes (for a CD-ROM disk).

Yes, a standard-size CD-ROM disk holds 650 megabytes, which is a lot!

It’s about   450 times as much as a high-density 1.44M floppy.

It’s about 1800 times as much as a 360K floppy.

Since 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).

CD-ROM disks store info differently than floppy & hard disks:

On a CD, each track is part of a spiral.

On a floppy disk or hard disk, each track is a circle.

On a CD, different tracks have different lengths and hold a different number of bytes.

On a typical floppy disk or hard disk, all tracks have the same number of bytes as each other.

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 the first CD-ROM drives that were invented, the transfer rate was the same speed as music CD’s: 150 kilobytes per second.

Then came drives that could spin twice   as fast: 300 kilobytes/second. That’s called double speed  or 2X.

Then came drives that could spin thrice  as fast: 450 kilobytes/second. That’s called triple speed or 3X.

Then came drives that spun four times as fast: 600 kilobytes/second. That’s called quad speed     or 4X.

Then came 4½X drives, then 6X, then 8X, then 10X, then 12X. During the summer of 1997, most drives sold were 12X, which transfers 1800 kilobytes/second.

Then came drives that were even faster. For example, you could buy a drive called 24X/12X (or 24X maximum or 24X max), whose outer tracks are read at a maximum speed of 24X, though the inner tracks are read at just 12X.

Now you can buy drives that go even faster: 72X max!

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 100 milliseconds is great.

100-200 milliseconds       is okay.

Over 200 milliseconds  is terrible.

Buying a drive

Here are the cheapest good drives:

Transfer rate      Seek    Buffer  Brand      Model               Price

48X max              65 ms     ¼M    Mitsumi    CRMCFX 48X      $53

62X max              90 ms     2M     Kenwood  UCR 420            $109

72X max            100 ms     2M     Kenwood  UCR 421            $125


Each of those drives is IDE. You can get those prices from these discount dealers:

Dirt Cheap Drives, 3716 Timber Drive, Dickinson TX 77539

phone 800-473-0960 or 281-534-4140

Megahaus, 2201 Pine Dr., Dickinson TX 77539

phone 800-786-1185 or 281-534-3919

Tri State Computer, 650 6th Ave. (at 20th St.), New York NY 10011

phone 800-433-5199 or 212-633-2530

Those prices are for just the bare drive; add $30 for an installation kit.

If you already own a CD-ROM drive that’s at least 2X, don’t bother replacing it by a faster one. Faster drives make most CD-ROM program run just slightly faster, since most CD-ROM programs are still designed under the assumption each CD-ROM drive is just 2X.

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 $30 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.

The most popular 24X-max multimedia kit is the Sound Blaster Discovery AWE64 24X, made by Creative Labs. You can get it for just $139 from discount dealers such as Harmony.

Tough installation

Warning: CD-ROM drives (and multimedia kits) are extremely difficult to install correctly because they tend to conflict with other hardware and software. Even if you follow the instructions in the setup manual, the stuff typically doesn’t work.

If you try to get help by phoning the company that made the multimedia kit (such as Creative Labs), you almost always get a busy signal. Even if you finally get through to a technician, the technician can’t help you much, since the technician doesn’t know enough details about the other hardware and software your computer contains.

Most consumers give up in disgust, return the stuff to the store, and pay the store about $70 to do the installation.

Some stores offer “free” installation — but do so by advertising a higher price for the CD-ROM drive.

When you buy a new computer, you can ask the salesperson to include a multimedia kit and install it. A computer that includes an installed multimedia kit is called a multimedia computer system.

Caring for your CD-ROM disks

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.

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.

The typical CD-ROM disk will last about 12 years. Then the aluminum on its surface will start to oxidize (corrode), and the CD will become unreadable.

CD-R

You can create your own CD’s, in the privacy of your home, if you buy a CD-Recordable drive (CD-R drive).

The cheapest popular CD-R drive is made by Mitsumi. It costs less than $195. That price is for a complete kit that includes the drive, the software, and 1 sample blank disk. Unfortunately, like most CD-R drives, it writes onto the CD slowly (at a speed of 2X) and reads from the CD slowly (8X). It also requires you to buy blank CD-R disks, which cost $1.20 each if you buy 5, $1.10 each if you buy 20, $1 each if you buy 50, 89¢ each if you buy 100. All those prices are from a discount dealer, Dirt Cheap Drives (800-473-0960).

Although a CD-R drive can write onto a disk, it cannot erase or edit what you wrote. For more flexibility, you can buy a CD-ReWritable drive (CD-RW drive), which can write onto a blank CD and then edit what you wrote.

CD-RW drives cost slightly more than CD-R drives. The cheapest CD-RW drive is made by Teac. It costs $199. That price is for a complete kit that includes the drive, the software, and 2 sample blank disk. The drive writes 4X and reads 32X. It uses blank CD-RW disks, which cost $1.60 each if you buy 5, $1.10 each if you buy 20, $1.04 each if you buy 100. It can also act as a plain CD-R drive (using plain CD-R disks), and it can read ordinary CD-ROM disks. All those prices are from Dirt Cheap Drives.

DVD

In 1997, the electronics industry began selling an improved kind of CD, called a Digital Versatile Disk (DVD). It looks like a standard-size CD but holds more info.

Unlike a standard CD, which holds just an hour of music or 650M of data, a standard DVD can hold a 2-hour movie (including the video and sound) or 4.7G of data. Since it can hold a movie, some movie lovers call it a “Digital Video Disk”, but it’s more versatile than just that!

A DVD can be recorded on just the bottom side (like a CD) or on both sides. (To use the second side, you must remove the disk from the drive and flip the disk upside down, like you’d flip a phonograph record.) A dual-sided DVD can therefore hold 9.4G of data.

An improved technology, called dual-layer DVD, puts nearly two layers of data on each side, so you get 8.5G per side, 17G total.

A DVD that contains computer data (instead of a movie or music) is called a DVD-ROM disk. To use it, put it in a DVD-ROM drive, which costs just $105. At that price, you get a drive that can read computer data but not Hollywood movies. To watch Hollywood movies, you’ll also need a Moving Picture Expert Group’s version 2 decoder card (MPEG-2 decoder card), which costs $99.

Every DVD-ROM drive can read DVD-ROM disks and also standard CD-ROM disks. Unfortunately, just modern DVD-ROM drives can also read CD-R and CD-RW disks.

To create your own DVDs in your own home, you can buy a DVD-Recordable drive (DVD-R drive), which is expensive. To create and edit your own DVDs, you must buy a DVD-RAM drive, which costs even more: $279. For a blank DVD-RAM disk holding 5.2G, you pay $37 for 1, $35 each if you buy 5, $33 each if you buy 10.