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GeForce FX 5800 Ultra (Reference Sample)
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| Mon Mar 03, 2003 | 3:18A| PermaLink |
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Like Radeon 9500 PRO, GeForce FX also uses a 128-bit memory interface, albeit with both the core and memory running at a much higher rate, so we see a similar pattern. Under the single texturing fill-rate test the bus would be unable to facilitate all 8 pixels and any other memory accesses in a single cycle, so the memory bus is flooded and stalls the pipeline, thus reducing the single texture fill-rate to about half its theoretical ability. And, in the case of the multi-texturing test because the 'loopback' texturing is in operation it would able to balance out the resources better. As the texture layers are applied over multiple cycles it means that the memory bus is not flooded all the time -- when a fully textured group of pixels is ready to be passed to the frame buffer the memory bus will not be able to sustain all memory accesses in one cycle, so anything that doesn't occur on the first cycle will stay in the FIFO buffer ready for the next cycle; as the rest of the pipeline is busy applying extra texture layers to the next groups of pixels the memory usage will be low and the rest of the memory accesses can be done then. At least, this is what we had seen with the 9500 PRO, though not with Geforce FX.
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FULL STORY @
BEYOND3D
(http://www.beyond3d.com/previews/nvidia/gffxu/)
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