AMD Athlon

Enhanced 3DNow!

AMD worked very closely with Microsoft as well as graphics card manufacturers to make sure that support for their Athlon was placed in Windows 98 SE and graphics card drivers. The support is not only for optimizing applications for the core of the Athlon, but also for the Athlon's Enhanced 3DNow! instruction set.

If you recall from the discussions earlier, 3DNow! brought SIMD execution to floating point operations that helped mask the weakness of the K6-2 and K6-III FPUs by providing an elegant way of improving performance. Those 21 instructions drew quite a bit of attention since their original implementation in 1998 and now have a very strong following in terms of support in games and in video drivers. The Athlon takes advantage of those 21 original instructions and adds 24 new instructions.

AMD included support for 19 new instructions that mimic the cache and streaming controls of Intel's SSE instructions, even using the same opcodes to maintain a level of compatibility between the two implementations. The cache and streaming controls are designed to help alleviate the effects of memory latency resulting from stalling the CPU pipeline.

The 5 remaining instructions that were added in for the Enhanced 3DNow! of the Athlon are digital signal processing extensions for soft modems, soft ADSL, complex math, MP3 and Dolby Digital decoding. Although the true performance benefits of the DSP extensions cannot be fully seen until implemented, the direction of such a move for AMD is definitely a positive one.

For the K6-2, 3DNow! offered a huge improvement in performance simply due to the lackluster performance of the K6-2's FPU however with the Athlon, this is not the case. The Athlon's FPU is already incredibly advanced and a very strong performer, and the effects of the Enhanced 3DNow! optimizations are essentially equal to the effects of SSE on the Pentium III, meaning that the improvement is there, just not as noticeable as with the K6-2.

As far as software/OS support goes, Microsoft's Windows 98 SE and DirectX 6.2 take advantage of the Athlon specific optimizations, including support for Enhanced 3DNow!