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Definition: MMX

(MultiMedia EXtensions) A set of 57 additional instructions built into the Pentium MMX chip in 1996 for improved multimedia and modem performance. MMX included a multiply-add instruction that provided the capabilities of a DSP chip found on sound cards.

MMX CPUs had to be switched into MMX mode, which turned the first 64 bits of the CPU's eight 80-bit floating point registers into MMX registers. When 8, 16 or 32-bit integers were loaded into the registers, they could be added and multiplied simultaneously. Starting with the Pentium III, MMX was superseded by Intel's Streaming SIMD Extensions (SSE), and floating point and multimedia operations were no longer mutually exclusive (see SSE).

MMX Registers
Simultaneous operations were performed when integers were loaded into the MMX registers.