L
ike a blender or any other electrically powered appliances, the computer runs on
electricity. Without electricity, a computer is just a slick looking collection of rather
expensive chunks of plastic, glass, and metal that have little value beyond keeping
yourdeskfromfloatingaway.However,thecomputeruseselectricity(actually,electrical
charges) in ways the blender can’t—at least not your everyday ordinary blender.
Tostoredata,acomputeralsousesafewnumberingsystems.Numberingsystems,such
as binary and hexadecimal (more on these later in this chapter), allow the computer to take
advantage of the some basic properties of electricity to create, store, and process data. To
understand what makes a computer tick, buzz, whir, and, of course, compute, you should
have a basic understanding of how electricity and the numbering systems are used in the
computer—which is exactly what we provide you in this chapter. It may seem like a math
lesson at times, but it’s painless, and you’ll be better informed for having read it.An Introduction to Digital Logic
You have most likely heard the termdigitalused with watches, clocks, calculators, and
other common items, but have you ever stopped to think about just what that meant?
Digital doesn’t mean that a device displays its information in digits, it means the device
creates, stores, and processes data using the two states of electricity—positive and neg-
ative (technically, it’s nonpositive, but more on that later). In effect, anything digital
uses some form of automated computation to operate. And yes, this definitely includes
the computer.
The opposite of digital is analog. An analog device expresses data as a continuing
electrical wave that usually has a varying frequency or amplitude that is sent over a car-
rier wave. Your home telephone is most likely an analog device that carries the sound of
your voice over the telephone wires with an analog signal wave. Other common analog
devices are radios and televisions (not counting High Definition Television—HDTV,
which is a digital device).
On the other hand, digital devices transmit, store, and process data using the
two-state properties of electricity. There are many digital devices around, such as CD
players, HDTV, and most of the stuff at Radio Shack and the Sharper Image stores.Digital versus Analog
Figure2-1illustratesthedifferencebetweenadigitalsignalandananalogsignal.Thedig-
ital signal is either one value or another; there are no in-between values. The digital signal
shown in Figure 2-1 illustrates this principle. Notice that the horizontal parts of the wave
line are either near the to por near the bottom with the wave line connecting either
straight u por straight down. When one value sto ps, the transition is immediate and the
other begins. As we will be discussing in the next few sections, the computer, because it is an
electricalappliance,iscapableofstoringonlydigitalvalues,andasaresult,isadigitaldevice.(^26) PC Hardware: A Beginner’s Guide