Although the unified shader concept is similar between the two cores, the way they go about presenting this functionality is a bit different. Whereas the G80 has 128 aptly-named “Unified Shaders”, the R600 has 320 “Stream Processors”. Clearly 320 is a bigger number than 128, but as we know in the hardware world, bigger numbers don’t always mean something is better. The fact of the matter is that Stream Processors are different than Unified Shaders. ATI’s Stream Processors are an integral part of the Superscalar architechture implemented on the R600. There are indeed 320 physical processors on the R600 CPU, but some of them are standard ALU’s and some of them are special-function ALU’s. NVIDIA has stated that they do not agree with how ATI counts their processors, proclaiming that they only count standard ALU’s on their G80 core. In any case, the approach to counting and placing these processors on the core differ between the two companies, so unfortunately nobody in their right mind will ever be able to compare these two things directly. That’s OK with us though, because we only really care about how the card performs.
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