Information Technology Reference
In-Depth Information
cables for computers, we first need to review some basic concepts
of wiring. Our discussion of computer cables follows from those
concepts.
At a minimum, two wires are needed for a complete circuit, just
as with most electrical circuitry. Think of one wire as fulfilling the
role of an electrical faucet, if you will, bringing electricity into the
device while the other wire has the role of the drain pipe and carries
the electricity away from the device. In making connections for
computers, wires usually come packaged as two (or more) metal
wires, each of which is surrounded by insulation. Often, the individ
ually insulated wires are, in turn, surrounded by a wrapper to keep
them together in a convenient package. Usually, the wires that you
plug into a power outlet are reasonably heavy to handle consider
able voltage and electrical current. Such wires, often called a
power
cord
, are usually bulky with a power plug at the end. For other con
nections, signals along the wires can work at low voltages and cur
rents, so the wires need not be heavy or bulky. Even at these low
voltages, however, the wires must channel electricity to the desired
destination without interfering with wires going elsewhere, which is
why all wires are securely covered in protective plastic insulation.
For reference later in this chapter, a few basic types of wiring
are shown in Figure 8.1. The cable on the left in this figure could be
used as a power cord. There are two individually wrapped wires of
moderate diameter, and these provide the basic electrical connec
tions that supply power and return it to a wall plug. The third wire
is a
ground
that provides an additional path for electricity from
your computer to the wall plug. In the cable in Figure 8.1, this third
wire also is wrapped with insulation. In other cables, the ground
may not be individually wrapped with insulation, but may appear
as a bare wire within the overall cable. The motivation for this
ground wire is safety; if something within the computer malfunc
tions, electricity coming in from the wall outlet might not be able to
return along the second wire as planned. The ground provides an al
ternate route, acting something like an overflow drain in your bath
tub or sink. Without this ground, if you inadvertently touched the
computer, the electricity might try to use your fingers and you to
complete the circuit, giving you a dangerous electrical shock. The
ground wire makes this much less likely.
Returning to Figure 8.1, the second cable from the left contains
four wires, arranged largely as a strip. In this flat cable, wires lie
