Hardware Reference
In-Depth Information
Chapter 4. Motherboards and Buses
Motherboard Form Factors
Without a doubt, the most important component in a PC system is the main board or
motherboard. Virtually every internal component in a PC connects to the motherboard, and
its features largely determine what your computer is capable of, not to mention its over-
all performance. Although I prefer the term
motherboard
, other terms such as
main board
,
system board
, and
planar
are interchangeable. This chapter examines the various types of
motherboards available and those components typically contained on the motherboard and
motherboard interface connectors.
Several common form factors are used for PC motherboards. The
form factor
refers to the
physical dimensions (size and shape) as well as certain connector, screw hole, and other
positions that dictate into which type of case the board will fit. Some are true standards
(meaning that all boards with that form factor are interchangeable), whereas others are not
standardizedenoughtoallowforinterchangeability.Unfortunately,thesenonstandardform
factors preclude any easy upgrade or inexpensive replacement, which generally means you
should avoid them. The more commonly known PC motherboard form factors include the
following:
Obsolete Form Factors
• Baby-AT (PC and XT)
• Full-size AT
• LPX (semiproprietary)
• NLX
• WTX
• BTX, microBTX, picoBTX
Modern Form Factors
• ATX and variants; microATX, FlexATX, DTX/Mini-DTX, and ITX/Mini-ITX
PC motherboard form factors have evolved over the years from the Baby-AT form factor
boardsbasedontheoriginalIBMPCandXT,tothecurrentATXformfactor(andvariants)
used in most desktop and tower systems. ATX has a growing number of variants, mostly
in smaller sizes designed to fit different market segments and applications. The short-lived
BTX form factors relocated major components to improve system cooling and incorporate
a thermal module.
