MMIX is a theoretical model of computer, which can be used for different educational purposes: learning of computer principles, explanation of software foundations, exploring the efficacy of algorithms etc. The author of MMIX is the famous scientist Donald Knuth.
MMIX is the second deeply developed Knuth's model: the first one, described nearly 40 years ago in the previous editions of his book "The Art of Computer Programming", was MIX. MMIX will totally replace MIX in future edittions of this book.
MMIX is based on RISC architecture and simulate a complex enough modern 64-bit computer.
D.Knuth wrote:
"How do you pronounce MMIX? I've been saying "em-mix" to myself, because the first "M" represents a new millenium. Therefore I use an article "an" instead of "a" before the name MMIX in English phrases like "an MMIX simulator".
Incidentally, the Dictionary of American Regional English (1996) lists "mommix" as a common dialect word used both as a noun and a verb; to mommix something means to botch it, to bollix it. Only time will tell whether I have mommix the definition of MMIX."
Note that MMIX also means 2009 as the Roman numerals. Probably it's a year when the author plans to complete working at his model.