It specifies the physical dimensions of the motherboard which will fit in the cabinet. Standard form factors ensure that parts are interchangeable across competing vendors and generations of technology.
The form factor drives which type of power supply can be installed in a system. Small form factors have been developed and implemented, but further reduction in overall size is hampered by current power supply technology. Various form factors are
|AT||12″ x 13”||Used till 1997|
|Baby AT||9″ x 10″||Smaller version of AT|
|ATX||12″ x 9.6”||Most popular and had many revisions|