ATX plug
The ATX connector is a 20- pin plug with reverse polarity protection, which is used to route the supply voltages from the power supply unit to the ATX board.
The connection wires from the power supply unit to the ATX board are color-coded and are used exclusively for the supply with DC voltage. Thus red wires stand for a DC voltage of +5 V, orange for +3.3 V, yellow for +12 V, blue for -12 V and black for ground.
There are also two control lines that transmit the signals for the switched on supply, Power On, and for the correct supply, Power Ok.