MMIX
MMIX (pronounced em-mix) is a 64-bit reduced instruction set computer (RISC) architecture designed by Donald Knuth, with significant contributions by John L. Hennessy (who contributed to the design of the MIPS architecture) and Richard L. Sites (who was an architect of the Alpha architecture). Knuth has said that: "MMIX is a computer intended to illustrate machine-level aspects of programming.