The
CPU is made up of one or more plastic boards that hold a large
number of electrical connectors and sockets. Attached to the
connectors are cables from other parts of the computer. Plugged
into the sockets are electronic parts called integrated circuits,
also known as IC’s or chips. Beneath protective plastic covers
the chips contain shiny, thin slivers etched with distinctive
patterns. The shiny material is primarily the element silicon,
a major ingredient in common sand.
The
pattern on a chip results from a manufacturing process that
turns ordinary silicon into an extraordinary device containing
hundreds or thousands of small electronic switches, known as
transistors. The microscopic circuit pattern on just one chip
is far more complicated than all the visible electrical connections
on the entire plastic board.
The
complex circuitry of one chip is made up of many repetitions
of just a few basic arrangements of transistors. The two main
arrangements are called bit cells and logic gates. A bit cell,
as the name indicates, can store one bit of information. Memory
chips ate made up mostly of bit cells.
Logic
Gates
Logic
gates are responsible for most of the actual processing of information.
The microprocessor, the most important chip in the computer’s
CPY, is primarily made up of logic gates. It is the chip that
actually carries out the instructions of the program. The logic
gates are the means by which a computer actually process information.
The gates open and close under certain conditions, creating
or breaking tiny electrical circuits.
The
operation of the microprocessor and its logic gates is best
understood by thinking of a bit of computer data not a number,
but as the answer to a true/false question. With numbers you
solve problems by doing arithmetic, but with true/false statements
like those in computers, you solve problems by performing logical
operations.
There
are three basic logical operations, AND, OR, and NOT, and three
corresponding gates. You can think of the gates as doors that
have specific requirements before they will open. When those
requirements are met, the door opens or remains closed, and
a logical operation has been performed. This works as follows.
An
AND gate has two input bits and one output bit. The output bit
us true (represented as 1) only if the first input bit is true
(1) AND the second input bit is true (1). If either or both
inputs are false (represented as 0), its output is false (0).
For example, a person could use and AND gate as a Friday t he
13th tester. One input would be the truth or falsity of the
statement, “Today is Friday.” The other input would be the truth
or falsity of the statement, “Today’s date is the 13th.” The
output of the AND gate will be true (1) only of the first statement
is true and the second statement is true.
An
OR gate also has two input bits and one output bit. A very superstitious
person who fears both Fridays and 13th’s might use it as a Friday
or the 13th tester. The OR gate would warn that person to beware
by giving a true output (1) when either the first statement
is true or the second statement is true.
A
NOT gate has only input and one output bit. They are always
opposite of each other. If its input is true (1), then its output
is false (0), that is, not true. If its input is false (0),
then its output will be true (1).
Logic
gates can do many things that are important to data processing,
such as comparing or adding two bits. In fact, data processing,
at its most fundamental level, consists of a series of AND,
OR, and NOT operations.
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