The

form factor is the most used form factor. Because of its popularity,

there are several versions of the ATX form factor. Each version has a different

specification for dimension and number of expansion slots. However, all the

variants share the following characteristics:

Back plate measurements $(($:${6\mathrm{.}25}^{\text{'}\text{'}}{1\mathrm{.}75}^{\text{'}\text{'}}\}$

Power supply specifications:

$24-$pin ATX power connector

On$/$off switch runs from the case to the motherboard

Soft$-$power control $($OS can turn the computer off$)$

Expansion slot locations and spacing $({0\mathrm{.}8}^{\text{'}\text{'}}$ between slots$)$

Mounting hole locations

CPU location $($top of board near power supply$)$

NLX

BTX

ITX

ATX