AT keyboard (DIN5) and PS/2 keyboards are in terms of electrical signals and the low-level framing protocol equivalent. As for the higher protocol level PS/2 is

AT keyboard (DIN5) and PS/2 keyboards are in terms of electrical signals and the low-level framing protocol equivalent. As for the higher protocol level PS/2 is technically an superset of AT keyboard, but when used on PC platforms (or with Linux) the difference does not matter. And in reality most of the cheap keyboards you can buy only implement small subset of the protocol that is used by BIOS and Windows, such keyboards will not work with things like DEC Alpha workstations. (this also leads to somewhat surprising observation that under windows some keyboards work when plugged into mouse port, some do not)