Originally created 11/18/96

Computers 101: What's inside that box anyway?

Even if you never plan to open the case of your computer, it's a good idea to know a bit about what goes on inside.

What to buy, when to buy it, when to upgrade and even when to bite the bullet on a hefty repair bill are all decisions that can be helped by having some understanding of how your computer is put together and what the individual parts do.

So, here's a tour of the inside of your computer. Relax: You don't need to be a computer engineer or a certified, card-carrying geek to open up a computer. Just be calm and careful.

The first thing to do is dig out your warranty. Why? You need to make sure that opening the PC doesn't void the warranty. Most manufacturers will allow minor tinkering, but there are things some manufacturers don't want you to touch.

Second, find your manual and make sure your unit isn't one of those one-piece PCs like the all-in-one Compaq Presario and some Macintoshes. With those units, you physically remove the computer's main board with the various option cards attached. If this is the case, we'd suggest you skip this exercise as being unenlightening (and, perhaps, downright dangerous).

Now, with all of that out of the way, let's get to the fun part. We're not actually going to move anything around, mind you; we're just going to look. It's a great little confidence builder, and a neat way to entertain a preteen on a rainy day.

The general procedure is pretty easy: 1. Unplug the computer and remove the cables tying it to the monitor, mouse, etc.; 2. Slide or lift off the cover according to your instruction manual. Read the manual carefully. With standard cases and towers, you usually have to loosen or remove a few screws along the way, and it can be pretty frustrating if you miss just one.

At this point, you'll be peering into what is probably the most complicated thing ever built by the human race. Think of it as a privilege, like exploring King Tut's tomb. Indeed, when I was born, more than 40 years ago, the wonderfully miniaturized electronics you're looking at would have taken up several Tut's tombs' worth of space.

Off to one side, where the electric cord plugs in and where the on/off switch is, there's a metal box about the size of four packs of cigarettes. It might be a cube shape, or it might be long and narrow, but it will certainly have some largish wires running out of it and a round grille on one side. That box is your power supply. It takes standard household current and steps it down to the lower voltages used by the PC.

Behind the little round grille is a fan, which serves both to cool the power supply and to direct air across the rest of the computer.

Be careful here: The power supply isn't something to fool with, since it can hold a hefty electrical charge for some time after you unplug the computer. That's because the power supply is also designed to stabilize the power to your computer. Household voltage can sag from 120 to 90 volts or jump higher, and the power supply will smooth the hills and valleys to deliver a constant voltage to the chips.

Next to the power supply, snug against one of the long sides of the case, is the computer's main board, most often referred to by the wonderfully descriptive (and perhaps sexist) term "motherboard." You can't miss it: It's relatively big; it's usually green or blue, traced with gold or silver lines; and it's studded with little electronic gizmos.

The gold and silver lines are, in effect, the wires that connect the gizmos together. If your computer gets really dusty and dirty, current can leak across these traces and cause malfunctions, which is why you should keep your case closed. If you have erratic problems with the PC, its worth using one of those little cans of air you can buy at computer stores to blow out the innards, removing dust.

The motherboard contains slots, some of which are occupied by expansion cards. These cards may connect your monitor to the rest of the computer and give you a place to plug in speakers. As computers have evolved, more functions of cards tend to be integrated into the motherboard, hence the need for fewer slots. One of the great variations among computers is whether they support functions directly from the motherboard or use cards in the slots. The former is cheaper; the latter, more flexible.

If you take a look at the connector that leads to your monitor, for example, you may see that it is plugged into a card that extends through the back of the computer. Or maybe there's no card, but instead a connector at the edge of the motherboard, which means video functions are integrated there.

The large black squares sprinkled randomly on the motherboard are "chips," or integrated circuits used to control various parts of the computer. The biggest square is usually the computer's microprocessor, sometimes called the CPU, or central processing unit. This is the thing that can be called a Pentium or a Power PC chip.

Among the other squares on the motherboard are ROM-BIOS (read-only memory-basic input-output statement) chips, which contain the rudimentary instructions the computer needs to start up, access its memory, disk drives and so on.

Arranged in four or eight rows of tiny slots, possibly with several slots empty, you'll also see things that look like tiny versions of expansion cards, with little black rectangles on top of them. Those are your memory modules, the part that comprises what's called DRAM (dynamic random access memory) or sometimes just RAM.

Look around a bit and you'll probably find a similar-looking module sitting off by itself somewhere. That's your secondary cache, a specialized type of memory. You may also find one or two of these memory modules mounted on the card that your monitor plugs into - that's video memory, or VRAM.

Finally, you'll probably see a couple of cables that look like big ribbons. Trace out one end of the cable and you'll see that it plugs into the back of a cigarette pack-sized box that's your hard disk, which is where your programs are stored. The other end of the ribbon will be plugged into either the motherboard or into its own expansion card. Another ribbony cable will connect your floppy-disk drive.