What is the difference between AT and ATX motherboards?
All Motherboards used to have the same rear connector layout for the keyboard and the same width from the days of the 286 into the early Pentium days. This is where the term, AT, came from. It was the form factor of the IBM AT PC Motherboard, which was very different from the XT systems. All of the Motherboards had a round, 5 pin DIN connector for the keyboard about 3/8″ in diameter. The keyboard connector was part of the Motherboard. It lined up with a hole in the rear of the PC’s case. The serial and parallel ports came from cables from an add on card. These mounted on the rear slots or knock outs on the rear. Later these ports were on the Motherboard with the IDE and floppy controllers, but they still had cables connecting the ports to the rear of the PC case. When the on board PS/2 mouse port became common, it just was one more cable from the Motherboard to the rear panel. A typical AT type case and Motherboard are shown below. The cards starting from the far right to left are a mo
