The PC motherboard form factors were: 1981: PC 1983: XT - more slots, closer together 1984: AT - 16 bit slots, taller cards 1985: Baby AT - eliminated the l

The PC motherboard form factors were: 1981: PC 1983: XT - more slots, closer together 1984: AT - 16 bit slots, taller cards 1985: Baby AT - eliminated the large non slot area 1987: PS/2 - changed most things, only keyboard/mouse and VGA connectors were adopted 1995: ATX - rotated Baby AT 90 degrees so tall components wouldn't interfere with cards 1997 and later: many ATX variations, BTX, ITX and so on