P4 may refer to any of the following:
1. The P4 connector is a 12V power supply cable used with motherboards that have an Intel Pentium 4 or later processor. Today, the connector is a standard power connector and is used with both Intel and AMD motherboards. As seen in the picture, the P4 cable has two black wires that serve as a ground and two yellow wires that are +12VDC and connect to a four pin connection on the motherboard.
If you have a new power supply with an 8-pin connector and a motherboard that needs a P4 connector, the 8-pin connector can be made into a p4 connector. All 8-pin connectors are backward compatible and are two 4-pin connectors connected to each other that can be separated.