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 overall performance. Although I prefer the term motherboard, other terms such as main board, system board, and planar are interchangeable. This article 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 standardized enough to allow for interchangeability. Unfortunately, these nonstandard form factors preclude any easy upgrade or inexpensive replacement, which generally means they should be avoided. The more commonly known PC motherboard form factors include the following:

Motherboards have evolved over the years from the original Baby-AT form factor boards used in the original IBM PC and XT to the current BTX and ATX boards used in most full-size desktop and tower systems. ATX has a number of variants, including microATX (which is a smaller version of the ATX form factor used in the smaller systems) and FlexATX (an even smaller version for the lowest-cost home PCs and some smallform-factor corporate PCs). The newest form factor, BTX, relocates major components to improve system cooling and incorporates a thermal module. BTX also has smaller microBTX and picoBTX variations. Another small form factor called Mini-ITX is also available; it's really just a minimum-size version of FlexATX designed for very small systems. NLX is designed for corporate desktoptype systems but has largely been replaced by FlexAXT; WTX was designed for workstations and medium-duty servers, but never became popular.

Although the Baby-AT, Full-size AT, and LPX boards were once popular, they have been replaced by more modern and interchangeable form factors. The modern form factors are true standards that provide improved interchangeability within each type. This means one brand of ATX boards can interchange with other brand ATX boards, BTX with other BTX, and so on. The additional features found on these boards as compared to the obsolete form factors, combined with true interchangeability, has made the migration to these newer form factors quick and easy. Today I recommend purchasing only systems with one of the modern industry-standard form factors. Each of these form factors, however, is discussed in more detail in the following sections.

Anything that does not fit into one of the industry-standard form factors should be considered proprietary. Unless there are special circumstances, I do not recommend purchasing systems with proprietary board designs. They will be virtually impossible to upgrade and very expensive to repair later because the motherboard, case, and often power supply will not be interchangeable with other models. I call proprietary form factor systems "disposable" PCs because that's what you must normally do with them when they are too slow or need repair out of warranty.