GNU MIX Development Kit (MDK). MIX is Donald Knuth’s mythical computer as described in his monumental work The Art Of Computer Programming. As any of its real counterparts, the MIX features registers, memory cells, an overflow toggle, comparison flags, input-output devices, and a set of binary instructions executable by its virtual CPU. You can program the MIX using an assembly language called MIXAL, the MIX Assembly Language.