it depends there are both 6pins and 8pins
ATX Ver 1.0 has one 20 pin port ATX Ver 1.1 has one 20 pin port and a 4 pin port ATX Ver 2.0 has one 24 pin port and a 4 pin port
the regular ATX has a 20 pin power connector, while the enhanced ATX power connector has 24 pin power connector.
A regular ATX motherboard uses a single 20-pin P1 connector with optional 4-pin auxillary power connector
24 pins