Encyclopedia of Electrical Engineering

The word "computer" comes from the word "compute", which means, "to calculate". Hence, people
usually a computer to be a calculating device that can perform arithmetic operations at high speed. In fact
the original objective for inventing a computer was to create a fast calculating machine. However, more
than 80% of work done by computers today is of non-mathematical or non-numerical nature. Hence, to
define computer merely as a calculating device is to ignore over 80% of its functions.
#### How computer works?

Any computer—regardless of its
type—is controlled by programmed instructions, which give the machine a purpose and tell it what to do.
The computers discussed here and which are everywhere around you—
are *digital computers*. Digital computers are so called because they work “ by the numbers." That
is, they break all types of information into tiny units, and use numbers to represent
those pieces of information. Digital computers also work in very strict sequences of
steps, processing each unit of information individually, according to the highly organized instructions they must follow.
A lesser-known type of computer is the *analog computer*; which works in a very
different way from digital computers. The
earliest computers were analog systems, and
today's digital systems owe a great deal to
their analog ancestors. Analog and digital
computers differ in many respects, but the
most important distinction is the way they
represent data.
Digital systems represent
data as having one distinct value or another;
with no other possibilities. Analog systems,
however represent data as variable points
along a continuous spectrum of values.
This makes analog computers somewhat
more flexible than digital ones, but not necessarily more precise or reliable. Early analog
computers were mechanical
devices, weighing several tons
and using motors and gears to
perform calculations.

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