The original ATX 20-pin main power connector used before ATX12V 2.x. Found on motherboards pre-2005. 24-pin PSUs often have a detachable 4-pin extension.
| Pin | Name | Function | Type |
|---|---|---|---|
| 1 | 3.3V | 3.3V power | PWR |
| 2 | 3.3V | 3.3V power | PWR |
| 3 | GND | Ground | GND |
| 4 | 5V | 5V power | PWR |
| 5 | GND | Ground | GND |
| 6 | 5V | 5V power | PWR |
| 7 | GND | Ground | GND |
| 8 | PWR_OK | Power good signal | I/O |
| 9 | 5VSB | 5V standby | PWR |
| 10 | 12V | 12V power | PWR |
| 11 | 3.3V | 3.3V power | PWR |
| 12 | -12V | Negative 12V power | PWR |
| 13 | GND | Ground | GND |
| 14 | PS_ON# | Power on active low | I/O |
| 15 | GND | Ground | GND |
| 16 | GND | Ground | GND |
| 17 | GND | Ground | GND |
| 18 | -5V | Negative 5V often absent | PWR |
| 19 | 5V | 5V power | PWR |
| 20 | 5V | 5V power | PWR |
The original ATX 20-pin main power connector used before ATX12V 2.x. Found on motherboards pre-2005. 24-pin PSUs often have a detachable 4-pin extension.