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.

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.

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".

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 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.

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.

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.

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.

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.

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 3½-inch high-density floppy drive. Here’s how it works.

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!

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.

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.

Popular IBM-compatible drives For IBM-compatible computers, four kinds of floppy drives have been popular:

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:

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.

Drives for other computers For other computers, many kinds of floppy drives have been invented:

Speed In the disk drive, the disk spins quickly. The exact speed depends on what size disk the drive uses.

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.

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).

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 $25. A disk teaching the computer how to handle a general business task (such as accounting, filing, or correspondence) usually costs about $100.

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.

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").

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.

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.

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.

The copy is called a backup. Use the backup disk when the original disk gets wrecked.

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.

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. It looks the same size as a standard floppy disk (3½ inches) but holds 100M, which is 70 times as much as a 1.44M floppy! It costs $18, but you can pay just $11 each by getting 6 at a time.

To use Zip disks, you must buy a Zip drive. It reads just Zip disks and costs $139. (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.

LS-120 The next step up is the laser servo 120M disk (LS-120 disk). Like a 1.44M disk and a Zip disk, an LS-120 disk is 3½-inch, but it holds more (120M). It costs $18, but you can pay just $16 each by getting 5 at a time.

To use LS-120 disks, you must buy an LS-120 drive. It reads LS-120 disks and 1.44M disks. It costs $170. It’s faster than a Zip drive. You can buy LS-120 drives made by O.R. Technology and Imation.

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.

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 4-gigabyte hard drive holds a non-removable stack of disks, and the entire stack totals 4 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.

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.

the main floppy drive is called drive A; the other floppy drive is called drive B.

the main hard drive is called drive C; the other hard drive is called drive D.

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.

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 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 90^th of a second, so it’s a 180^th 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.

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.

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.

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).

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.

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) are 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.

A totally different fast scheme is the Small Computer System Interface (or SCSI, which is pronounced "scuzzy"). It’s used on most Mac hard drives and the biggest IBM-compatible hard drives.

The newest, fastest version of SCSI, called Ultra Wide SCSI, can transfer 40 megabytes per second. You can buy Ultra Wide SCSI drives that hold up to 23.3 gigabytes.

IBM-compatible drives Modern, popular IBM-compatible hard drives are IDE, hold 4, 5, or 6 gigabytes, and cost about $60 per gigabyte. For example:

For a drive that’s Enhanced IDE (or Fast ATA-2 or Fast ATA-3), the best kind of card is an IDE accelerator, which costs $30 ($35 minus $5 discount). For Ultra IDE drives, get an Ultra IDE card instead, which costs $50. For Ultra Wide SCSI drives, get an Ultra Wide SCSI controller card instead, which costs $249. In the table above, the "+$33" or "+$50" or "+$199" is for those cards.

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).

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.

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.

To use modern programs on an IBM-compatible computer, you must make sure the hard disk contains some fundamental software, called MS-DOS and Windows. The newest version of MS-DOS (version 6.22) consumes over 5 megabytes. Windows 3.11 consumes over 10 megabytes. That makes 15 megabytes altogether! (Windows 95 consumes even more: just the "important" parts of Windows 95 consume over 35 megabytes!)

Buy at least a 2-gigabyte drive. A 2-gigabyte drive costs just slightly more than a 1-gigabyte drive and will last you for many years. You’re buying peace of mind!

If you need more than 23.3 gigabytes, attach several hard drives together. 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).

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.

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.

Transfer rate The speed at which the drive spins is called the transfer rate. The higher, the better!

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.

Now most drives are even faster! The fastest drives are called 24X/12X (or 24X maximum or 24X max): their outer tracks are read at a maximum speed of 24X, though their inner tracks are read at just 12X.

Seek time The average time it takes for the head to move to the correct track is called the average seek time.

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 $239 from discount dealers such as Harmony.

Those prices are from a discount dealer called USA Flex (444 Scott Dr., Bloomingdale IL 60108, 800-USA-FLEX or 708-582-6206).

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.

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.

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.

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.

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 the Sure Store CD-Writer, manufactured by Hewlett-Packard. It costs just $380. Unfortunately, like most CD-R drives, it writes onto the CD slowly (at a speed of 2X), reads from the CD slowly (6X), and requires that you buy a SCSI card. It also requires you to buy blank CD-R disks, which are pricey: $3.99 each if you buy 1, $3.49 each if you buy 10, $2.99 each if you buy 30. All those prices are from a discount dealer, USA Flex (800-444-4900).

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.

Unfortunately, CD-RW drives are expensive. The cheapest is made by Ricoh and costs $600. That price includes a SCSI card. The drive writes 2X and reads 6X. It requires you to buy blank CD-RW disks, which are very expensive: $26 each if you buy 1, $24 each if you buy 10, $22 each if you buy 30. Those prices are from USA Flex.

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.

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 about $500.

To create your own DVDs in your own home, you can buy a DVD-Recordable drive (DVD-R drive), which costs about $10,000. To create and edit your own DVDs, you must buy a DVD-RAM drive, which costs even more.