Originally posted by GuitarFreak1857
that's ATX power. 24 pin is 20 pin + 4 pin. it depends on your motherboard. the newer mobos support 24 pin
one more time, just exactly what he said. older motherboards support 20 pin, some newer mobo's support 24 pin. since PSU's want to stay compatible, some have choosen a 20+4 solution that you can use in either a 20 OR a 24 pin configuration.
Pick your mobo, see what power connector is has either 20 or 24, then choose your PSU based off of that. Well, also taking into consideration amperage, dual 12v rails, and wattage of course.