(^312) PC Hardware: A Beginner’s Guide
E
verything in a computer runs on electricity. Even the data is just positive or negative
electrical values stored in transistors and capacitors. Without electricity, there would
be no computer, or at least as it is known today. It would probably look more like an
abacus. Fortunately, there is electricity and there are computers—but there is a catch.
Electricity as it exists in the everyday world, running appliances, lighting lights, enter
taining the masses, cooking, cooling, and much more, isn’t the kind of electricity that a
computer is designed to use. The computer must convert the electricity that comes for the
wall socket and turn it into the type of electricity it can use. The PC’s power supply is charged
(pardon the pun) with the task of converting electricity for the PC. This chapter is about how
the computer uses electricity and how it gets into the form the computer can use.
Understanding Electricity
Electricity flowing through a circuit is like water flowing through a hose. When the water
faucet is opened, the pressure in the water line forces the water to flow into the hose at
some gallons-per-minute rate. Friction reduces the force and rate of the water before it
exits the hose. When electricity flows into a wire from a source such as a battery or the
wall outlet, some of its pressure is lost to resistance in the wire.
The water in the hose can be measured in terms of its gallons-per-minute and water
pressure. The forces involved with the flow of electricity through a wire or circuit is
measured in volts, amps, and ohms. Table 14-1 compares the measures used in the water
hose to their electrical equivalents.Counting Electrons
As indicated in Table 14-1, electricity can be measured, and this extends to the electricity
inside the computer. Each type of measurement tells you something different about the
circuits in the computer. Here is a brief overview of each of these electrical measures and
how each is used: Amps An amp is a measure of the strength in a circuit or its rate of flow. The
amp rating on a device indicates the amount of current needed to operate the
device. For example, a hard disk drive needs about 2.0 amps to start up, but
only 0.35 amps for its normal operation.
Ohms An ohm measures a conductor’s resistance to electricity. Conductors
are covered later, but for now a conductor is a wire that carries an electrical
flow. For example, if the resistance in a circuit is less than 20 ohms resistance,
then current can flow through it.