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 ones that are +12VDC. All of these wires attach to a four pin connection on the motherboard.
If you purchase a new power supply with an 8-pin connector and your motherboard only needs a P4 connector, you can separate the 8-pin into two 4-pin sections.