Datasheet

Identifying Motherboards
21
Your PC stores the settings in a special memory chip called the CMOS chip. To retain
these settings, the CMOS chip requires power constantly. To prevent the CMOS chip from
losing its charge, a small battery is located on the motherboard. The CMOS chip holds
the BIOS.
System Board Form Factors
Form factor refers to the size and shape of a component. Most system boards today use
the ATX form factor. Some of its key features are its orientation of the expansion slots
parallel to the narrow edge of the board, a one-piece power connector from the power
supply, the built-in I/O ports on the side, and the orientation of the CPU in such a position
that the power-supply fan helps to cool it.
An older, alternative form factor for a system board is the baby AT style. This type uses
a two-piece power supply connector, uses ribbon cables to connect ports to the board, and
orients the expansion slots parallel to the wide edge of the board.
A case is generally designed to hold one or the other of these motherboard form factors,
and a power supply is designed to work with one or the other; therefore, those three com-
ponents must be chosen as a group.
Jumpers and DIP Switches
Jumpers and DIP switches are used to configure various hardware options on the
motherboard. Processors use different voltages and multipliers to achieve their target
voltage and frequency. You must set these parameters on the motherboard by chang-
ing the jumper or DIP switch settings. Figure 1.9 shows a jumper and two types of DIP
switches. Individual jumpers are often labeled with the moniker JPx (where x is the
number of the jumper). These are far less common than they used to be; many settings
are now congured through the BIOS.
FIGURE 1.9 A jumper set and DIP switches
Jumper "Rocker-type" DIP switch "Slide-type" DIP switch
Cases
The case is the metal or plastic box in which the motherboard, power supply, disk drives,
and other internal components are installed. A case is typically—but not alwayspurchased
with a power supply already installed.
Choosing the right case for the motherboard is important. Recall from the preceding
sections that motherboards come in two form factors: ATX and AT. Each requires a differ-
ent style of case and a different type of power supply.
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