MMX is special processing circuitry built into Pentium processors. To a programmer, it appears as 57 special instructions for accelerating multimedia operations and communications within the PC. Benefits include improvements in audio and video playback, image processing, and 3D rendering. Intel has said it will incorporate MMX instructions in all its future processors.
PCs including the MMX technology have begun reaching the market. Typical features include 32 Mbytes of main memory, a 2-Gbyte hard drive, a 6X or better CD-ROM drive, 16-bit sound system, and Super VGA graphics.
Functionally, MMX processing uses single instruction, multiple data (SIMD) techniques to perform one calculation simultaneously on multiple data elements. Making such operations possible is a 64-bit register into which the processor packs multiple operands of 8, 16, or 32 bits each. Mathematical operations can take place simultaneously on each operand occupying this register. To prevent overflow conditions, MMX also uses saturating arithmetic which limits the value of math functions.
MMX instructions are written to help programmers avoid the need to branch to remote sections of the program. This heads off slowdowns resulting when a processor must fetch code from an unexpected memory location.
MMX resembles Risc processing in that most MMX instructions execute during one clock cycle. Many of these are frequently used in graphics and image manipulation. For example, one instruction performs a high-speed multiply- accumulate, computing the sum of a series of products. This is a key operation in digital signal processing as often applied in applications such as telephony and process control.