2. Features of classic SIMD extensions

2.1 SIMD registers

Defining SIMD instructions on the 32-bit registers of 32-bit processors or the 64-bit registers of 64-bit processors was of limited interest, since it would have been of no real interest for floating-point computing and would have been limited to computing on bytes and 16-bit words for integers. With the exception of the aforementioned MMX extension of IA-32 with 64-bit registers, SIMD extensions took off with special 128-bit registers (SSE and Altivec series), then later with 256-bit registers.

Table 1 shows the number of SIMD registers and their sizes for the various versions of...