Computers: Not Just a PC on a Desk
by Don Lindsay
Everyone has seen a computer. You probably saw a keyboard, and a
mouse, and a screen. And it's easy to think that all computers look
like that, and that they always did, and always will.
If you've taken a computer course, you may have heard that a
computer contains a microprocessor. And you may know that a processor
works by fetching instructions from a memory. But if you click on
some of the links below, you will see some examples that are just a
Not all computers do just one instruction at a time. Recent microprocessors are "superscalar". This means
that it sometimes executes more than one instruction per tick of the
clock. That was the original DEC Alpha chip, which could execute 2
instructions per clock: its bigger, denser
successor can do 4 per clock. Of course, you can always string
together 6,768 microprocessors when one
Not all electronic computers are
Electronic logic can be built from
vacuum tubes, magnetic amplifiers, magnetic core,
- Not all computers are electronic. Digital logic can be built
from gears, relays, fluidics, LEGO, and a
variety of optical devices. In the future, we hope to compute with
quantum dots, or organic molecules.
- Not all computers sit on desks. Some were quite
And, at that time, a
computer was also pretty large.
- Not all computers plug in to the wall, and some
, with wireless communications.
Computer scientists have paid a lot of attention lately to
the issues of intermittent connection. Also, there have
been discussions of the fundamental incompatibility between
using little electrical power, and delivering high compute power.
(Many computers have used a hundred kilowatts,
and some had to be cooled with liquid nitrogen or liquid helium.)
- Not all computers stay in an office. We can take a computer into
the field , where ever the problem is. We
have computerized everything from subway tires to wildlife . And a few computers have
travelled hundreds of millions of miles.
- Not all computers are controlled from a keyboard: some have
and more recently some have
- Not all computers work on personal problems. Some served
: some study
: though some just play
. (This last is the very first video game, SpaceWar.)
- Not all computers have displays and keyboards, and interact with users.
Rugged "embedded" computers have been in planes and missiles since the
1960's. A program re-trims the control surfaces (or the missile's nozzle attitudes ) at least a dozen times a
second. Recently, we've built stealth bombers
and fighters which have terrible
aerodynamics, and would fall out of the sky if the control computer
failed. A pilot simply wouldn't be able to control them: they are
- Not all computers have their programs in their memory.
and Colossus, the first electronic computers, were programmed by placing patch
wires into plugboards. The tangles of wires in the picture
the program. (Only part of ENIAC is in the picture - it was 100 feet
was "programmed" in the same sense - you adjusted the mechanism.
- Not all computers have a program. In systems analysis,
you do not use a system: you are part of a system. So,
operated because its users were there: its program was its geometry.
(It wasn't the first computer: we have found remnants of a Woodhenge.)
Last modified: 9 July 1997
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