MMIX was published in 1999, a time when it wasn't decided that x86, and later AMD64 and ARMv7/8 would dominate all platforms. Back then, Alpha had only recentl

MMIX was published in 1999, a time when it wasn't decided that x86, and later AMD64 and ARMv7/8 would dominate all platforms. Back then, Alpha had only recently been killed, and things Itanium were coming up, Apple sold PowerPC computers and Windows devices running ARM, MIPS and SuperH were being widely sold. In the spirit of 1999, a fantasy architecture was not a bad way to gloss over that fragmentation. Also, x86 is not an elegant teaching platform (though I hear AMD64 is much better).