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No matter how smart you are, you wouldn't know anything if you couldn't remember. Thoughts and ideas would go in one neuron and out another, forever lost in the entropy of the universe. You know things because you can call back thoughts and ideas, to work on them again or just talk about them. A computer, too, needs some way of retaining its thoughts. Like you, it needs both short-term memory for holding ideas while it works on them and long-term memory to store all the facts and old ideas that, by chance, it might need another day.

The short-term memory of computers is often called simply memory. The long-term memory is often termed mass storage and involves several technologies. Hard disk drives hold the ideas you put into the computer, both commercial programs and your own original data. Floppy disks and optical drives (CDs and DVDs for the most part) store the ideas of others than you want your computer to access. Tape drives provide a safety net, keeping a duplicate copy of your computer's most important ideas.


Just as you need your hands and workbench to hold tools and raw materials to make things, your computer's microprocessor needs a place to hold the data it works on and the tools to do its work. Memory, which is often described by the more specific term RAM (which means Random Access Memory), serves as the microprocessor's workbench. The amount and architecture of the memory of a system determines how it can be programmed and, to some extent, the level of complexity of the problems it can work on. Modern software often requires that you install a specific minimum of memory—a minimum measured in megabytes—to execute properly. With modern operating systems, more memory often equates to faster overall system performance.

In today's computers, memory usually comes in subassemblies called memory modules that plug into special sockets on the main circuit board of your computer. Most computers have three or more of these sockets in a group, one or more of which is filled with a memory module as standard equipment.

Hard Disk Drives

Long-term memory is where you store thoughts and ideas that, although you don't need them immediately, you need to know—stuff like your shoe size, which doesn't come up in everyday conversation (at least not among normal adults) but becomes a handy factoid when musing through a mail-order catalog. Your computer's hard disk holds such factoids along with all the other stuff it needs to know but not at this exact moment—such as the instructions for programs you're not using, financial records you hope the auditor will ignore, term papers you someday hope to publish as best-selling fiction, and even extra designs for wallpaper for your computer screen. Your computer's hard disk lets you call on any of those stored facts on a microsecond's notice.

Most hard disks take the form of a sealed box, typically silver and black with a green circuit board dotted with tiny electrical components on the bottom. A hard disk connects to the main circuit board of your computer through that interface we talked about earlier via a short, wide, and flat set of wires, called a ribbon cable because it looks like a ribbon (although an admittedly strange gray ribbed ribbon).

Floppy Disk Drives

Once upon a time, some computers lacked hard disk drives and instead used floppy disk drives ("once upon a time" being in the unbelievable past, a little before Cinderella cleaned out fireplaces). Inexpensive, exchangeable, and technically unchallenging, the floppy disk served as a data interchange system for years because it was based on well-proven technologies and was mass produced by the millions.

Today, the floppy disk drive is found on nearly every computer, but functionally it's about as useful to your computer as an appendix. (Granted, an appendix won't fit into a drive slot, but you get the idea.) In today's world the floppy disk is slow and holds too little information, so it is gradually disappearing from computers, replaced in function by any of a variety of optical drives.

The computers that still have floppy disk drives usually wear them proudly, out in front. On desktop systems, it's usually the uppermost drive in the case. From the outside you see only a long, black slot about three-and-a-half inches wide with a rectangular button near one corner. Notebook computers put their floppy disk drives, if they have one, wherever they fit—usually hidden in the side of the computer under the keyboard.

Optical Drives

Getting new memories into your computer is the primary job served by optical drives. They store programs and data in a convenient form—small discs—that's standardized so that you can exchange the discs (and memories) between computers. (Note that due to a strange quirk of design and origin, magnetic drives use "disks" whereas optical drives use "discs.")

Optical discs currently come in two flavors: Compact Discs and Digital Versatile Discs. These are the CDs and DVDs you slide into your home entertainment system. In either form, discs are cheap and easy to copy, so software publishers have made the CD-ROM their preferred means of getting their products to you, with DVDs slowly replacing CD-ROMs because of their higher capacity. You can create your own optical disks with a suitable drive to store either data for your computer or music and video for your entertainment systems.

A CD-ROM or DVD drive is usually the other drive on the front of your desktop computer, bigger than the floppy and featuring a volume control and headphone jack (should you want to slide a music CD into the drive). You'll know what it is as soon as you press the eject button and the tray rolls out. On a notebook computer, manufacturers stuff their optical drives wherever they fit, usually on the side near the back of the computer.

Tape Drives

Tape is for backup, pure and simple. It provides an inexpensive place to put your data just in case—just in case some light-fingered freelancer decides to separate your computer from your desktop; just in case the fire department hoses to death everything in your office that the fire and smoke failed to destroy; just in case you empty your Recycle Bin moments before discovering you accidentally deleted all your exculpatory tax records; just in case an errant asteroid ambles through your roof. Having an extra copy of your important data helps you recover from such disasters as well as those that are even less likely to happen.

Tape drives are optional on personal computers. They add enough cost that people would rather risk their data. On larger computers (the servers used in business), tape drives are more common because the cost of restoring data is so high, probably thousands of times the cost of a drive, that their use is justified.

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