22 Computer Service and Repair
Cooling Fan
The cooling fan supplies a constant stream of
air across the computer components. The typical
CPU comes equipped with a fan mounted on the
CPU to assist in the cooling process, as shown in
Figure 1-23C. Electronic components are damaged
by excessive heat.
Cables
There are several types of cables commonly
used inside the PC case. These cables connect the
motherboard to devices such as the hard drive
and optical (CD/DVD) drive.
Figure 1-33 shows two types of cables used
to connect a hard drive and optical drive to the
motherboard: SATA and PATA. The acronym
SATA represents Serial ATA, and the acronym
PATA represents Parallel ATA. Hard drives and
optical drives originally used an ATA cable
which looks similar to the PATA cable in that it
consists of many parallel conductors. Some of the
conductors in an ATA and PATA cable are used to
transfer data. Others are used to transmit control
signals between the motherboard and the device.
The SATA cable uses fewer individual wires
to achieve much higher data rates than PATA.
The individual wires in a SATA cable are twisted
together. This allows the cable to carry higher
frequencies, which results in higher data rates.
The design is based on electronic engineering
principles. A great deal of study is required to
fully understand the principles applied to the
cable design. For now, consider any cable designed
with twists to be able to achieve a higher data rate
than a cable designed without twists.
Electrical power for SATA and PATA devices
can be transmitted through the cable conductors
(wires), but many devices consume more electrical
power than the cables and motherboard are
designed to safely carry. When a large volume of
electrical power is required for a device, a separate
power cable that runs directly from the power
supply is used.
eSATA cables (not shown) connect external
hard drives and optical drives. eSATA technology
is slightly different than SATA. The PATA, SATA,
and eSATA technologies are discussed in detail in
Chapter 9—Storage Devices.
How the Major Parts Work
Together
The following scenario traces how a sequence
of events occurs in a typical PC system. In this
example, a user moves from turning on the
computer through saving text data. Please note
that there are many different PCs. They all have
unique start-up features and program interactions.
1. When the power switch is turned to the on
position, electrical power from the wall outlet
moves through the power supply where it
is converted to a much lower dc voltage (or
voltages). This stepped-down power is used
to run the major components of the computer
system including the motherboard, hard
drive, and expansion cards. The fan starts
up, providing a rush of cool air across the
components.
2. Next, the fi rmware system is activated and
performs a POST. The POST (power-on self-
test) checks the components in the computer
such as RAM, ROM, hard drive, and keyboard
to ensure they are in proper working order.
Information, such as the type and model
number of the fi rmware and the amount of
memory, will fl ash across the computer’s
monitor, providing information.
Figure 1-33. SATA and PATA cables used to connect a hard
drive and optical drive to the motherboard.
PATA
SATA
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