(MMX) (NOT an acronym for "MultiMedia eXtension", according to Intel, but an Intel brand name) A set of 57 extra instructions built into some versions of Intel's Pentium microprocessors for supporting SIMD operations on multimedia and communications data types.

MMX-enhanced processors are due to be released early in 1997. They will be fully compatible with previous Intel processors and software but software will only benefit if it is written to use the new instructions. They can handle many common multimedia operations, such as digital signal processing, normally handled by a separate sound card or video card.