Editing MMX

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'''''MMX''''' was a set of [[SIMD]] multimedia instructions developed by [[Intel Corporation]] that enabled enhanced performance for applications coded to support it. It has been implemented in all Intel processors since the [[Intel Pentium MMX|Pentium MMX]], and all [[Advanced Micro Devices|AMD]] processors since the [[AMD K6]].

''MMX'' was initially rumoured to stand for ''MultiMedia eXtensions'' or ''Multiple Math eXtension'', but officially it is a meaningless initialism trademarked by Intel.

To simplify the design, and to avoid modifying the operating system to preserve additional state through context switches, ''MMX'' re-uses the existing eight [[IA-32]] [[FPU]] registers. This made it difficult to work with [[Wikipedia:Floating-point arithmetic|floating-point]] and SIMD data at the same time. To maximize performance, [[programmer]]s must use the [[processor]] exclusively in one mode or the other, deferring the relatively slow switch between them as long as possible.

Another problem for ''MMX'' was that it only provided [[integer]] operations. Each of the eight [[64-bit]] ''MMX'' vector registers, aliased on the eight existing floating point registers, could represent two [[32-bit]] integers, four [[16-bit]] short integers, or eight [[8-bit]] chars. When ''MMX'' was originally developed, the use of vectored-integer operations made sense (both [[2D]] and [[3D]] setup required it), but as systems moved to utilize graphics cards for this work, ''MMX'' fell out of favour and vectored floating-point operations became much more important.

Intel later addressed these shortcomings with [[SSE]], a greatly expanded set of SIMD instructions with 32-bit floating-point support and an additional set of [[128-bit]] vector registers that made it easier to perform SIMD and FPU operations at the same time.

Intel's main competitor, AMD, built upon ''MMX'' with their [[3DNow!]] instruction sets while another competitor, [[Cyrix]], developed their own version of ''MMX''; instead of directly copying Intel's MMX (as AMD were allowed to do due to their cross-license patent agreement with Intel), they reverse-engineered the ''MMX'' instruction set, with the intention of extending it, much like AMD did. The end result was called [[Cyrix MMX]].

Intel's development of [[SSE2]] rendered ''MMX'' effectively obsolete, although MMX continues to still be supported in Intel processors for software specifically optimized for it that do not take advantage of SSE2.

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