MMX Primer

The MMX technology is designed to accelerate multimedia and communications applications by including new instructions and data types that allow applications to achieve a new level of performance. It exploits the parallelism inherent in many multimedia and communications algorithms, yet maintains full compatibility with existing operating systems and applications. 
A wide range of software applications, including graphics, MPEG video, music synthesis, speech compression and recognition, image processing, games, video conferencing and more, shows many common, fundamental characteristics: 

  • small integer data types (for example: 8-bit pixels, 16-bit audio samples) 
  • small, highly repetitive loops 
  • frequent multiplies and accumulates 
  • compute-intensive algorithms 
  • highly parallel operations 

The MMX technology is designed as a set of general purpose integer instructions that can be applied to the needs of the wide diversity of multimedia and communications applications. The highlights of the technology are:

  • Single Instruction, Multiple Data (SIMD) technique 
  • 57 new instructions 
  • 8 64-bit wide MMX registers, named mm0 up to mm7
  • 4 new data types 

MMX technology introduces four new data types: three packed data types (bytes, words and doublewords, respectively being 8, 16 and 32 bits wide for each data element) and a new 64-bit entity. Each element within the packed data types is an independent fixed-point integer. The architecture does not specify the place of the fixed point within the elements, because it is up to the developer the control of its place within each element throughout the calculation. This adds a burden on the developer, but it also leaves a large amount of flexibility to choose and change the precision of fixed-point numbers during the course of the application in order to fully control the dynamic range of values.
The four MMX technology data types are: 

  • Packed byte — 8 bytes packed into one 64-bit quantity 
  • Packed word — 4 16-bit words packed into one 64-bit quantity 
  • Packed doubleword

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