| Chips
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. |
