The 5-pin DIN keyboard connector used with the first IBM PC (1981) and second-generation IBM AT (1984). It was subsequently replaced with the smaller 6-pin Mini-DIN connector on the IBM PS/2 in 1987.

But there’s one thing we’re sure of: if you find yourself reading the original POST code for the PC-XT ... of the old board, [Anders] needed a little IO, specifically video and keyboard.