Full AT
Commonly referred to as the AT and full-size AT, the Full AT is a motherboard form factor introduced by IBM in August of 1984 and was widely used in the 1980s. The Full AT is 12" wide x 13.8" deep and only fits into a full size AT tower case that support this form factor. Today, this form factor is rarely found or used and has been replaced by ATX and Baby AT. Below is an example of what an early IBM AT motherboard looked like.
Also see: AT, ATX, Baby AT, Form factor, Motherboard definitions, P8 and P9 connector