AT

Form Factor The AT form factor is the oldest and the biggest form factor. It was popular until the Baby AT was released, which was around the time of the 386 processor (1992-93). The reason that prompted the Baby AT was the width of the AT (12") and the fact that the board was difficult to install, service, and upgrade. BABY ATThe Baby AT was the standard in the PC industry from roughly 1993-1997. It is still being used today, usually in Pentium class products. Some issues with the AT and Baby AT design is the location of the features on the board. The CPU socket is placed so that it may interfere with longer bus cards. In some designs the memory sockets are similarly placed. This can limit the amount and selection of peripheral cards you can install. Also the IO ports are separate and mounted on the case and connected to pin-outs on the motherboard. These are usually located near the floppy and IDE pin-outs and can result in quite a jumble of ribbon cables.