1. +12V: Used for peripherals like floppy drives, hard drives, and fans.
2. +5V: The main power supply for the motherboard and most components.
3. -12V: Used by some older components, though less common in modern systems.
4. -5V: Used by some older components, though less common in modern systems.
5. +3.3V: Used by some components, particularly modern CPUs and other high-speed components.
While +3.3V is less common in the AT standard, it is crucial to remember that it's still produced by most modern power supplies.