Datasheet

22 Chapter 1
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Hardware
One case may also be distinguished from another in terms of its orientation. A desktop
case lies with its widest side flat on the desk; a tower case stands up on end.
Finally, one case differs from another in terms of the number of drive bays it has. For
example, within the broad category of tower cases are mini-towers (typically with two
large and two small drive bays), mid-towers, and full towers (typically with four large and
three small drive bays). However, there is little standardization of the number of drive bays
that constitute a particular size; one manufacturer’s full tower may have more or fewer
bays than another’s.
Although it isn’t common, you may occasionally encounter a slim-line case, which is
a desktop-orientation case that is shorter and thinner than a normal one—so short that
normal expansion boards won’t fit perpendicular to the motherboard. In such cases a riser
card is installed, which sits perpendicular to the motherboard and contains expansion slots.
The expansion cards can then be oriented parallel to the motherboard when installed.
Shapes
Form factor refers to the size and shape of a component. There are five popular mother-
board form factors for desktop PCs:
AT AT (Advanced Technology) is an older style of motherboard. A slightly more modern
variant of it is the baby AT, which is similar but smaller. Its key features are a two-piece
power-supply connector, ribbon cables that connect the I/O ports to the board, and an
AT-style keyboard connector. The expansion slots are parallel to the wide edge of the
board. See Figure 1.10.
FIGURE 1.10 An AT-style motherboard
CPU
Expansion slots
parallel to wide edge
Power supply
connector
AT-style
keyboard
plug
COM and LPT
ports (require
ribbon cables)
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