The P1 power connector is the first ATX power supplies and motherboards used a single power connector. It also has 20 pins.
A P1 connector is a power connector found on ATX power supplies. It is used to provide main power to the motherboard, and to control ACPI functionality (tell the power suppy to turn off and back on).
P1 connector
P1
P1
20 pin P1 connector.
p1
P1
A regular ATX motherboard uses a single 20-pin P1 connector with optional 4-pin auxillary power connector
ATX version 2.2 allowed for 24-pin P1 connector, which is backward compatible with the 20-pin P1 connector.
24
12v, 3.3v 5v
The expansion slot that requires extra power is the PCI Express (PCIe) slot. To accommodate the increased power demands of high-performance graphics cards, the PCIe standard added an additional 4 pins to the older 20-pin P1 power connector, creating the 24-pin ATX power connector. This modification allows the motherboard to supply more power to components like GPUs, which often require significant electricity for optimal performance.