MMX Extensions: A name applied to extensions introduced to the Intel 80x8x instruction set in 1996. These extensions allow 8 byte (4 word, 2 double word) parallel integer operations to be performed using operands stored in the Floating Point (FP) registers. Parallel/Vector operations (which, incidentally have been around since the 1960s) are executed in parallel on multiple operands. The MMX instructions perform rapid integer addition, subtraction or multiplication according to rather complex rules as well as providing for moving, packing and unpacking data. The MMX instructions are hypothesized to have considerable potential utility in providing sound and video processing in low end future "686" class and later computers . Cyrix licensed MMX. AMD eventually developed a similar 3D-Now instruction set.

Basically, MMX put the signal analysis portion of a digital signal processor on the CPU. Unfortunately, signal processing using integer arithmetic requires a great deal of programming skill, and translating between integer and floating point in order to use MMX generally ate up most of the potential time savings even if the MMX operations could be programmed. In retrospect, MMX was not particularly useful although it was a marketing success.

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