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:

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 info on CD-ROM disks is hard to edit.

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”.

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:

Here’s their history:

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 system unit. If the drive is internal, it’s built into the system unit. If your computer is standard, the drive is internal, but some Macs have external drives instead.

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:

Then 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 info onto the disk.

Here’s how to write new info onto 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 info 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 info 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 so old and primitive that it has just one read-write head, it uses just one side of the disk and is called a single-sided disk drive.

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:

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

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 can lack any distinguishing marks. Too bad!

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.

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.

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, as follows: 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.

Speed In the disk drive, the disk spins quickly.

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 computer cannot understand what an IBM PC writes.

When you go into a computer store to buy a disk containing 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.

If your computer is so old that it uses 5¼-inch disks instead of 3½, you face these headaches:

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 put whatever info 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 & sectors on the disk by erasing all the old tracks & sectors and all your old data!

Remember:

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 Micro Center (1100 Steelwood Rd., Columbus OH 43212, 800-634-3478).

For example, here are the prices from Micro Center for double-sided disks:

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.

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 you’ve lost it or 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: the disk! Unfortunately, the magnetic signals on a disk are easy to destroy.

One way to accidentally destroy them is to put your disk near a magnet; so keep your disk 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 or on a sunny windowsill or 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.

A 3½-inch floppy disk comes in a strong jacket. If you’re using a 5¼-inch or 8-inch floppy disk instead, beware: its jacket is too weak to protect it from pressure; don’t squeeze it; don’t put it under a heavy objects (such as a paperweight or book); to write a note on the disk’s jacket, don’t use a ballpoint 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 so ancient that it’s made by Commodore or Radio Shack and is not an IBM clone, you face this headache:

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.

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.

Hard disks are better than floppy disks in three ways:

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), cost about $30,000, held 100 megabytes, and required a minicomputer or mainframe.

Life has gotten smaller! 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, and fits in a desktop microcomputer. Some notebook computers use even smaller 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.

Copy from floppy to hard & back

When you buy a program, it usually comes on a floppy disk or a CD-ROM disk. Put that floppy disk or CD-ROM disk into its drive, then copy the program from that disk to the hard disk. (To copy by using an IBM-compatible PC, 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 holds more info and works faster than the floppy disk or CD-ROM 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, very close to the disk (just a tiny fraction of an inch above the disk), so close 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.

After the head reaches the correct track, it must wait for the disk to rotate, until the correct sector reaches the head.

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.

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.

How many sectors?

How many sectors do you get on a track?

Early schemes 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.

IDE 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-100, it transfers 100 megeabytes per second instead of 33.3. You can buy Ultra ATA-100 drives holding up to 120 gigabytes.

SCSI 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:

IBM-compatible drives Modern, popular IBM-compatible hard drives are Ultra ATA-100, hold 40, 60, or 80 gigabytes, and cost about $2 per gigabyte, so:

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-100 drives:

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

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

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 July 2002. By the time you read this book, prices might be even lower.

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 Buy at least a 40-gigabyte drive. A 40-gigabyte drive costs just slightly more than a 20-gigabyte drive and will last you for many years. You’re buying peace of mind!

It’s much cheaper to buy a 40-gigabyte-megabyte drive now than to buy a 20-gigabyte-megabyte drive now and another 20-gigabyte-megabyte drive later.

Another reason for buying a 40-gigabyte drive is that it will act faster than a 20-gigabyte drive.

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 $37 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:

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.

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:

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

The standard CD-ROM disk has a diameter of 12 centimeters (which is about 5 inches) and holds 650 megabytes.

The CD-ROM disk is single-sided: all the data is on the disk’s bottom side — the side that doesn’t have a label.

The disk contains 2 billion pits, 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 CD can hold 99 tracks, totaling an hour of music (for an audio CD) or 650 megabytes (for a CD-ROM disk).

650 megabytes is a lot! It’s about 450 times as much as a high-density 1.44M floppy! Yes, a single CD-ROM disk can hold as much info as a stack of 450 high-density 1.44M floppies!

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 info! Moreover, a CD-ROM disk costs less than $1 to manufacture (once you’ve bought the appropriate CD-ROM-making equipment, which costs several hundred dollars).

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

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 a music CD’s: 150 kilobytes per second. That speed is called 1X.

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

Then came 3X drives, then 4X, then 4½X, then 6X, then 8X, then 10X, then 12X. During the summer of 1997, most drives sold were 12X, which transfers “12 times as fast as 150 kilobytes per second”, which is 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! In modern CD-ROM drives, the average seek time is 100 milliseconds or less.

Brands

Here are the cheapest good drives:

Each of those drives is IDE and includes a 128K buffer. You can get those prices from these discount dealers:

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. Standard computers include a multimedia kit, already installed.

Tough installation

Warning: CD-ROM drives (and multimedia kits) are hard to install 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, you usually 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 just 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.

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). It can write onto blank CD-R disks, which used to be expensive but now are cheap.

The cheapest way to get the CD-R disks is to look for sales at chain stores. For example, while I was writing this book in July 2002, Best Buy was having a sale where you get 100 CD-R disks for a total cost of “$30 minus $27 in rebates”, giving a final cost of $3. Yes, that’s just $3 for 100 disks, making the disks cost just 3¢ each!

Although a CD-R drive can write onto a disk, it cannot erase or edit what you wrote.

CD-RW

For more flexibility, you can buy a CD-ReWritable drive (CD-RW drive), which can write onto a blank CD-RW disk and then edit what you wrote. CD-RW drives used to be expensive, but now they’ve become nearly as cheap as CD-R drives, so nobody bothers selling CD-R drives anymore.

The cheapest fast CD-RW drive is made by Memorex.

During some weeks, there are discounts on other CD-RW drives. For example, when I was writing this book in July 2002, Best Buy was selling a Samsung 32x10x40 CD-RW drive for just $40 ($100 minus $60 rebates).

You can get blank CD-RW disks for just 66¢ each if you buy 25 at a time from discount dealers such as Micro Warehouse (800-367-6808). Those disks are rated just for 4X; 10X-rated disks cost more.

Creating your own CD (by using a CD-R or CD-RW drive) is called CD burning (because the data is burned into the CD), so CD-R and CD-RW drives are called CD burners.

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 slightly more than a CD-ROM drive. 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.

Comp-USA sells a DVD-ROM drive made by Hi-Val for $40 ($60 minus $20 rebates). That drive is called “16X” because it rotates 16 times as fast as a plain DVD drive. The drive also acts as a 40X CD-ROM drive. Its seek time is 95-millseconds.

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 $60.

To create and edit your own DVDs in your own home, buy a DVD+RW drive, such as the Sony DRU120A, available for $429 ($479 minus $50 rebate) from PC Connection, which sells blank DVD+RW disks for $8 each. When buying the drive and blank disks, make sure you order DVD+RW (instead of DVD-RW or DVD-RAM, which are incompatible).