the regular ATX has a 20 pin power connector, while the enhanced ATX power connector has 24 pin power connector.
ATX version 2.2 allowed for 24-pin P1 connector, which is backward compatible with the 20-pin P1 connector.
24
A regular ATX motherboard uses a single 20-pin P1 connector with optional 4-pin auxillary power connector
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
24 pin
24 pin
24
I think AT used 20 pins, and ATX introduced 24 pins.
enhancer atx motherboard
Enhanced ATX
The P1 power connector is the first ATX power supplies and motherboards used a single power connector. It also has 20 pins.