AT power supply delivers +5 V, +12 V, -5 V and -12 V voltages using two six-pin connectors. A few newer boards used an aditional connector for +3.3 V. Note, that you must install these connectors to the motherboard in a way that the black wires are placed on the center, or your equipment will be damaged.
P8 AT power supply connector
| Pin | Name | Color | Description | |
|---|---|---|---|---|
| 1 | PG | Orange | Power Good, +5 VDC when all voltages has stabilized. | |
| 2 | +5V | Red | +5 VDC (or n/c) | |
| 3 | +12V | Yellow | +12 VDC | |
| 4 | -12V | Blue | -12 VDC | |
| 5 | GND | Black | Ground | |
| 6 | GND | Black | Ground |
P9 AT power supply connector
| Pin | Name | Color | Description | |
|---|---|---|---|---|
| 1 | GND | Black | Ground | |
| 2 | GND | Black | Ground | |
| 3 | -5V | White or Yellow | -5 VDC | |
| 4 | +5V | Red | +5 VDC | |
| 5 | +5V | Red | +5 VDC | |
| 6 | +5V | Red | +5 VDC |
Cable connector is Molex 90331.
The original PC debuted in 1981 and used two cables to connect the
PSU (power supply) to the motherboard. The two cables plug side by side
into the motherboard connectors. Sometimes they are keyed so they only
plug in one way and sometimes they aren't. Even if they're keyed you can
insert them the wrong way if you put a little effort into it. You
always have to remember to plug them in so the black wires are next to
each other.
In old PCs, almost all of the chips ran directly off of the 5 volt
rail. As a result the PSU delivers most of its wattage at 5 volts. There
are three or four lines dedicated to the 5 volt rail. The other main
rail is 12 volts. That was used primarily to run disk drives, motors,
and fans. The two negative rails are bias supplies which only have to
provide small amounts of current.
P10 AT aux power supply connector (rarely seen)
|
Pin |
Name |
Color | Description | |
| 1 | GND | Black | Ground | |
| 2 | GND | Black | Ground | |
| 3 | GND | Black | Ground | |
| 4 | 3.3v | Green | +3.3 VDC | |
| 5 | 3.3v | Green | +3.3 VDC | |
| 6 | 5v | Green | +5 VDC |
The aux power cable was added to provide extra wattage to motherboards for 3.3 and 5 volts.
