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.

It was a beautiful unit, but confusing, as this keyboard comes with an 8-pin DIN connector. A 5-pin DIN plug or 6-pin Mini-DIN would be easy to work with, but what was this odd connection?