(^48) PC Hardware: A Beginner’s Guide
Storing Electricity
Transistors store a bit value as electrical voltage. The amount of electrical power used in a
transistor is not very large. Most of the earliest microprocessors used 5 volts of direct
current (DC), and the newer processors now use as little as 2.2 volts DC (VDC). A transis-
tor stores data by switching between high and low voltage, which represents the binary
1s and 0s, respectively. For example, in a 5 VDC processor, a charge of +5 volts is the high
voltage and represents a binary 1, and a charge of –5 volts is the low voltage and repre-
sents the binary 0.
One problem with using a higher voltage level to store a value in a transistor is that
switching between these two voltage values, as much as 10 volts total, does take a certain
amount of time. By reducing the voltage, to 2.2 VDC for instance, the range of change is
smaller, it takes less time, and the microprocessor can do more.
By decreasing the voltage of a microprocessor from 5 VDC to as low as 2.2 volts, Intel
and other manufacturers were able to dramatically increase the speed of their systems.
Another benefit of reducing the voltage is that it reduces the amount of power needed to
run the computer—very important for portable computers—and reduces the heat generated
by all those transistors.Integrated Circuit
I have used the term integrated circuit a few times in this chapter and it’s time for a brief
description of just what that is. Anintegrated circuit (IC)is a combination of electronic
components, such as transistors, capacitors, and resistors. An IC is designed to fulfill
some logical function and can be built to be a timer, counter, a bank of computer memory,
or even a microprocessor.
The basic building block of an IC is a logic gate. Alogic gateperforms the Boolean algebra
AND operation by testing two input signals (each stored in a transistor). If both are positive
(representing true or 1), it sets the signal of a result value to positive. Otherwise, the value
is set to negative (representing false or 0).The Microprocessor
The microprocessor is a multifunction integrated circuit that is, in essence, the computer.
The processor, which is also called the central processing unit (CPU), is made up of
several parts. These parts work together to carry out the instructions and actions that
translate to a word processing system or a game on your PC.
The primary parts of the CPU, as illustrated in Figure 3-3, are as follows: Control Unit (CU) At the risk of being obvious, the control unitcontrols
the functions of the CPU. It is kind of like the manager who coordinates the