MMX (instruction set)

MMX is a single instruction, multiple data (SIMD) instruction set designed by Intel, introduced in 1997 with its P5-based Pentium line of microprocessors, designated as "Pentium with MMX Technology". It developed out of a similar unit introduced on the Intel i860, and earlier the Intel i750 video pixel processor. MMX is a processor supplementary capability that is supported on recent IA-32 processors by Intel and other vendors.

MMX has subsequently been extended by several programs by Intel and others: 3DNow! and ongoing revisions of Streaming SIMD Extensions (SSE).

MMX is officially a meaningless initialism trademarked by Intel; unofficially, the initials have been variously explained as standing for MultiMedia eXtension, Multiple Math eXtension, or Matrix Math eXtension.

AMD, during one of its numerous court battles with Intel, produced marketing material from Intel indicating that MMX stood for "Matrix Math Extensions". Since an initialism cannot be trademarked, this was an attempt to invalidate Intel's trademark. In 1995, Intel filed suit against AMD and Cyrix Corp. for misuse of its trademark MMX. AMD and Intel settled, with AMD acknowledging MMX as a trademark owned by Intel, and with Intel granting AMD rights to use the MMX trademark as a technology name, but not a processor name.

MMX defines eight registers, called MM0 through MM7, and operations that operate on them. Each register is 64 bits wide and can be used to hold either 64-bit integers, or multiple smaller integers in a "packed" format: a single instruction can then be applied to two 32-bit integers, four 16-bit integers, or eight 8-bit integers at once.

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