At the core of every computer is its capacity to remember things: sets of
instructions, particular files you've created, how much memory is left, where
you put your keys.
Computers store all this memory in two distinct ways. The main memory bank is
called the hard drive. It stores all the files you save on your computer and all
software programs you install. The capacity of a hard drive is usually somewhere
around 50 gigabytes of memory (about 5,000 megagytes); while RAM can only deal
with about 64 megs at a time.
RAM is a repository of all the programs and files you're operating at the
moment. It stands for Random Access Memory, and can't be accessed in the
long-term. As you type up a document, for instance, all the on-screen changes to
make are effected through RAM; but once you hit your "save" button, the file is
physically recorded on your hard drive.
If you were to break through your PC's plastic shell to get a peek at the
actual, physical hard drive, you'd find a flat box about the size of a small
notebook. Inside that box is one (or up to eight) "platters" -- disks that are
slightly smaller than CDs, and a little thicker. They're made of glass or metal,
coated with a magnetic film, and when your computer's on they clock several
thousand revolutions per minute. The data on each platter is gleaned by
"read-write heads," small arms that slide along the disks much like the needles
on record players. Read-write heads scan both sides of each platter, and either
retrieve previously stored information, or record new sets of data as you save
RAM, on the other hand, is constructed of a strip of small, flat chips. The
entire component is no bigger than your toothbrush. As you work on your
computer, these chips access memorized functions to let you, say, italicize a
word or close a window.
Finally, as with all things in life, the hard drive and RAM are best seen in
terms of a food analogy. If the hard drive were your pantry, RAM is the frying
pan. You can't make anything without stirring it around on the stove; but you
can't fry anything that wasn't stored in the pantry first. And when you're done
with it, whatever's left goes back in the pantry. Or the fridge, freezer,
whatever. Anyway, you get the point.