...any what does it do?
Well, there's no good name to distinguish the computer part of the computer setup from the whole setup, so we computer people usually call it "just the computer part", or maybe "the box", "the case", or something else, though those refer to specific pieces, also. The hard drive is where the data lives that survives a reboot. The RAM holds the data while it's being manipulated. The CPU (central processing unit) does practically all of the actual work. You might have a floppy drive or a CD-ROM drive. The motherboard is the big circuit board that all of that stuff is attached to. The power supply turns wall electrical current into something the computer can use.
The computer is the part that's not the monitor, mouse, or keyboard.
Here's one like we have on campus, first with the case lid on, then with
the case lid off. (OK, I cheated: the picture with the case on is of
a different computer, but it's more or less the same.)
The naming of parts...
Some of that in better detail...
The motherboard is the flat green thing in the bottom and everything that's permanently attached to it.
The CPU, or Central Processing Unit, is what actually does most of what a computer does. When you run MS-Word, this is where that program is being executed. When you type "decde", this is what runs the spellcheck thingie decides that's not a word; it then instructs the graphics card to underline it in red (or whatever). It's the brain.
In the picture below, the CPU is the little metallic rectangle in
the middle of the big green board. It's about the size of my little
fingernail: it's tiny. CPU manufacturers keep making the connections
inside these things smaller and smaller (they're measured in nanometers!),
so they can fit the millions upon millions of connections needed to make
these things go into things that big. The green card is about 1.5 inches
Below is an image of the CPU removed from its socket. Each dot on the
CPU (left) is a pin that must fit precisely into the hole in the socket
(right) meant for it. One bent pin and it's Game Over. Fortunately,
most folks never have a reason to take this apart.
Absent from these images is the CPU cooler, which is a combination of a heat sink and a fan. It's the black thing labeled "1" in the images at the beginning of this page. Its job, shockingly, is to keep the processor cool, which is a mighty big job. Even at that small size, a CPU can generate enough heat to melt itself, which would, naturally, be bad.
If the computer is working on something, the CPU is doing that work, but it must keep its data somewhere. Persistent data (that which exists between reboots) lives on the hard drive, but data that's in use lives in RAM (Random Access Memory).
Incidentally, it's called RAM because the computer can get at any piece of it without having to wade through all of the data before that piece. Think of it like the difference between audio CDs and tapes: with a CD, you can jump to some track and start playing, but with a tape you have to wind through everything before the song you want. Tapes operate as Sequential Access Memory; CDs are more like Random Access Memory. You may hear the term ROM thrown around as a contrast to RAM, also: ROM means Read Only Memory, and simply indicates that you can't, under normal circumstances, change what that thing knows. Most CDs are ROM-style.
RAM is little: this piece is just bigger than a stick of Big Red
chewing gum. This one holds about 128 megabytes of data.
When computers load programs into memory, this is where they go. Your computer must have at least as much RAM as it has programs to run (and the operating system, Windows for many folks, counts as a program). If you have less RAM than the running programs need, things get slow, because the hard drive is used instead of RAM to hold those programs. Hard drives are very, very slow compared to RAM.
On the left below is a floppy disk drive. On the right is a CD-ROM
drive. The flat grey ribbon cable coming out of these things is for
data transmission; the colorful cables are for electricity. Unplug
either and the item stops working.
Pictured below is a power supply. This thing's job is to take power from
the wall (110 volts AC 60Hz, more or less) and turn it into the sorts of
power the motherboard and drives want to consume, which is DC at 1.5,
3, 5, and 12 volts, most of the time. Each color of wire carries a
different voltage. This power supply ("PSU") is about the size of a
man's fist. Some of them are bigger than the average head.
The hard drive is where the computer keeps (practically) everything that
it remembers between reboots. Your programs, documents, cutesie little
icons, saved email... everything lives here. Lose this and you might
as well have lost the whole thing. (Lose the rest and we can rip out
the hard drive and cram it into another computer, and everything will
be essentially as it was.) Here are two hard drives; each is about
3" wide, 6" long, and 1" deep.
They're called "hard disk drives" because the thing that stores the data
is rigid, which is in contrast to the part of a floppy disk drive that
stores the data (it's flexible, floppy, non-rigid). Next time you have
a floppy disk you don't need anymore, carefully pop off the slide
thing then rip the plastic casing in half: you'll expose a grey thing
that's the magnetic doodad where your data lived before you did this.
(This procedure will destroy the disk, and if you're not very careful
you'll cut yourself, so please be careful.)
In a hard drive, though, the magnetic surface is on a metal platter: it
doesn't bend. It's hard to tell in the photo here, but each platter is a
lot like a metal CD. Each drive might have just one, or it might have as
many as five or six; all are strapped permanently and very tightly to a
central spindle, the shiney disc seen above. The head, which is a tiny
magnetic reader/writer near the open loop on the end of the arm shown in
the picture (between thumb and forefinter), moves around on the platters,
which spin, very much like a record player. Here's that head doing its
thing (with a little help):
Never ever open a hard drive. If dust gets in there, your data is in jeopardy; if you get a fingerprint on the platter (like I did: look closely), Game Over. Data recovery firms that specialize in slurping data from damaged drives have "clean room" facilities that filter out every conceivable speck of dust in the area. Technicians wear full body space-suit sorts of things. Only once all that's in place do they pop open the drives to try to get at your data. (That's part of why it costs so much: the facilities alone are very expensive.)
If you're into physics or mechanics, you might be wondering how they keep the drive heads from hitting the platters without introducing heat, friction, oil, and various other bad things. There's a powerful rare-earth magnet (neodymium, usually) in there. In this picture, it's under the yellow stickie-note under the palm of that guy's (er, "my") hand. Don't blow up your Morehouse hard drive... but if you ever have a dead drive at your disposal, it's fun to dig out that magnet and play with it. It's a lot stronger than you'd expect. Don't lose a finger in the attempt.
And there you have it! Contact the HelpDesk if you have any questions about this or any computing matter at Morehouse. If you want to see computer guts, we often have them sitting around.