PC Hardware in a Nutshell, 3rd Edition

Form Factor

Motherboards differ in size, shape, position of mounting holes, power supply connector type, and port types and locations. Together, these differences define the form factor of the motherboard. Form factor is a critical issue when you upgrade a system because the replacement motherboard must physically fit the case and use the existing power supply connectors. Form factor doesn’t matter when you’re building a new PC. You simply select the best motherboard for your needs, and then buy a case that fits it. Many motherboard manufacturers build similar motherboards in different form factors. Here are the form factors you may encounter:

AT, Baby AT (BAT), and LPX

All of these form factors are based on the motherboard used in the original 1984 IBM PC AT and are obsolete. The most recent of these motherboards use chipsets and processors that are two or more generations out of date. Although a few such motherboards remain available, they are suitable only to replace failed motherboards in obsolete systems that for some reason must remain in service. Other than that, there is no good reason to buy one of these obsolete motherboards. A system that uses this form factor is too old to be economically upgradeable.

ATX and variants

Nearly all current motherboards use the ATX form factor, or one of its smaller variants, the miniATX, μATX, FlexATX, and NLX. For a complete discussion of these form factors, including case and power supply issues, see Chapter 25 and Chapter 26.

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