Launched in 1998 with the K6-2, AMD intended the 3DNow instruction set to compete with Intel's SSE, which powered the Pentium 3.3DNow! accelerates the calculation of floating point numbers using the FPU, as opposed to MMX which only works for integers using the ALU. Like SSE it is an SIMD (single instruction, multiple data) instruction set allowing the same calculation to be applied to more than one set of data simultaneously.
For Folding@home, 3DNow! was used by the Gromacs cores on CPUs where SSE was not available (typically processors based on K6-2 and -3 and the Athlon series before SSE support was added). As it was slightly less efficient than its Intel-developed rival for Gromacs, it was not selected by default if SSE was available, but the huge boost in performance it provided over unoptimised code justified its inclusion as a fallback for when SSE was not available.
AMD has however announced that it is ending support for 3DNow!, meaning future processor generations may not support it. AMD's decision should not cause problems for many apps, except maybe older ones that are no longer maintained, and AMD provides a guide for programmers on how to convert their 3DNow!-optimised programs to use SSE instead. Support for two 3DNow! instructions will be retained in future generations however: PREFETCH and PREFETCHHW, which allow data to be preloaded into the L1 cache of the processor.
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Source: Tom's Hardware France
jmn
On: 08/28/10
