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Motherboard Form Factors
By Stephen Bucaro
The "form factor" of a motherboard defines its dimensions. You need to make sure that
the computer case that you purchase can accommodate the form factor of the motherboard
that you select. It is also wise to select a motherboard with a commonly available form
factor in case you need to replace it.
The original IBM PC used over a hundred discrete digital circuit chips, so the
motherboard was very large. With greater integration, IBM was able to reduce the size
of the motherboard and released the AT (Advanced technology) form factor. The AT
motherboard was still quite large. Further integration resulted in the release of
the "Baby AT" form factor.
The "Baby AT" form factor was quite popular, but it was designed when keyboard, mouse,
I/O, and video circuitry where contained on circuit boards that where plugged into
"expansion slots" on the motherboard. Manufacturers wanted to put this circuitry
"on-board" to the motherboard to save cost.
In 1995 the ATX form factor was designed to define standard locations for the keyboard,
mouse, I/O, and video connectors to allow for on-board circuitry. The continuing
increased integration of electronics allowed for smaller motherboards, so the Micro
ATX form factor was defined.
Smaller computers use less materials and are cheaper to manufacture. Smaller computers
also cost less to warehouse and to ship. Consumers like smaller computers too, because
they take up less space on the desk top. Manufacturers where able to shrink the size
of the case by putting the expansion slots on a separate circuit board, called a "riser
card", that plugs into the motherboard.
The LPX and Mini LPX form factors where designed for the riser board configuration.
The NLX is an even smaller form factor designed to accommodate a riser board.
Many computer manufactures use proprietary form factor motherboards. If you needed to
replace the motherboard in a computer made by on of these manufacturers, you can not
use a standard form factor replacement. You are forced to pay a high price for the
manufacturers proprietary motherboard. That's one of the many reasons it's better to
build your own than to buy a brand name computer.
The BTX (for "Balance Technology eXtended") form factor was released by Intel to
improve the thermal dissipation of the motherboard and accommodate PCI Express slots
which require a 24-pin power connector (the ATX uses a 20-pin connector). The BTX
format has three sizes:
the BTX is 10 x 12.8 inches,
the microBTX is 10.5 x 10.4 inches, and
the picoBTX is 10.5 x 8 inches.
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