E
verything a computer can do for you, that is, all of its magic, is controlled by its
microprocessor. At the heart of every computer is a microprocessor, which is designed
toperformallofthearithmetic,logic,andotherbasiccomputingstepsthatmakeup
the actions of your PC. What you see as a word processor, a computer game, a World
Wide Web browser, your e-mail, or any of the other software programs you perform on
your PC, are in fact hundreds, even thousands of instructions that the microprocessor
executes one at a time to carry out the actions of each program. Theprocessor, which is
short for both microprocessor andcentral processor unit (CPU), is a piece of electronic
circuitry that uses digital logic to perform the instructions of your software.
In this chapter, you are introduced to the processor and its functions. Included in this
discussion are the following topics: Digital logic
The binary number system
The construction and manufacturing of a microprocessor
The development and evolution of the microprocessorAn Introduction to Digital Logic
Before you get too dee pinto the digital circuits and logic of the processor, you must first
understand some fundamentals that underlie the way the computer and the processor
use electricity. It is perfectly normal for you to think of the computer as just another elec-
trical appliance, like a refrigerator, television, vibrating recliner, and so on. Sure, you
plug it in, turn it on, and it works. What could be simpler? Ah, but there’s a catch: it really
isn’t that simple.Two-State Logic
Like the light switch on the wall, the electricity in the computer is either on or off. Data is
stored in the computer with electrical charges that are either on or off. In the early days of
the computer,vacuum tubes, which were about the size and shape of small light bulbs,
stored data by turning individual tubes on or off. In today’s computers, this same concept
is applied on a much smaller scale with the transistor. Like the vacuum tube, thetransistor
holds an electrical charge that is—yes, you guessed it—on or off.
Actually, the electrical charge in a transistor is one of two distinct electrical voltage
levels. A higher voltage level represents one value, and a lower voltage level represents
another value. Because the computer has only these two electrical states in which to store
data, the data has to be either very simple, or some means must be used to allow multiple
transistors to be grouped to represent more complex data.
If all you ever need to store in the computer is on or off, true or false, yes or no, this or
that, ying or yang—two-state values that can be represented as two voltage levels—then(^40) PC Hardware: A Beginner’s Guide