What is a computer?
We have used the word computer many times in the preceding paragraphs, and
although we did not say so explicitly, we used it to mean a mechanism that does
two things: It directs the processing of information and it performs the actual
processing of information. It does both of these things in response to a computer program. When we say "directing the processing of information," we mean figuring out which task should get carried out next. When we say "performing
the actual processing," we mean doing the actual additions, multiplications, and so forth that are necessary to get the job done. A more precise term for this mechanism is a central processing unit (CPU), or simply a processor.
Fig. 1: A processor board, vintage 1980s
Twenty years ago, the processor was constructed out of ten or more 18-inch
electronic boards, each containing 50 or more electronic parts known as integrated circuit packages (see Figure 1). Today, a processor usually consists of a single microprocessor chip, built on a piece of silicon material, measuring less than an inch square, and containing many millions of transistors (see Figure 2).
Fig. 2: A microprocessor, vintage 1998
However, when most people use the word computer, they usually mean more
than the processor. They usually mean the collection of parts that in combination form their computer system (see Figure 3).
Fig. 3: A personal computer
A computer system usually includes,
in addition to the processor, a keyboard for typing commands, a mouse for clicking
on menu entries, a monitor for displaying information that the computer system
has produced, a printer for obtaining paper copies of that information, memory for
temporarily storing information, disks and CD-ROMs of one sort or another for
storing information for a very long time, even after the computer has been turned
off, and the collection of programs (the software) that the user wishes to execute These additional items are useful in helping the computer user do his or her
job. Without a printer, for example, the user would have to copy by hand what
is displayed on the monitor. Without a mouse, the user would have to type each
command, rather than simply clicking on the mouse button.
So, as we begin our journey, which focuses on how we get less than 1 square
inch of silicon to do our bidding, we note that the computer systems we use
contain a lot of other components to make our life more comfortable.