CertiGuide to A+ (Core Hardware)  9  Chapter 0001:  Power Supplies - System Board       9  IV  Power Supply Form Factors

IV  Power Supply Form Factors 1 ATX Power Supply

The first common form factor is known as an AT power supply. Two features distinguish the AT power supply from its relative. An AT power supply has a mechanical switch used to control the availability of AC power.

The second feature that makes an AT power supply instantly recognizable has the power connectors for the motherboard, sometimes called a system board. An AT power supply has two power connectors for the motherboard - labeled P8 and P9.

Computer manufacturers faced one challenge when working with the AT power supply. Remember the fact that the AT power supply uses a mechanical switch to supply power. That makes it impossible to turn the computer on remotely. To accomplish remote power-on, a small redesign on the power supply was needed. That redesign is found in the ATX power supply.

IV  Power Supply Form Factors 1 ATX Power Supply