how come the nvidia card is so much better then the 2900xt when the 2900 has a much higher clock speed, as well as 2x the stream processors? what else tells you which card is better by looking at the specs?
8800 series has more Texture mapping units and Render Output Pipelines
8800GTX has 32 Texture mapping units and 24 Render Output Pipelines
HD2900XT has 16 Texture mapping units and 16 Render Output Pipelines
The Stream processors in 8800GTX runs at 1.35GHz, but the Texture mapping units and Render Output Pipelines runs at 575MHz
In HD2900XT, the stream processor, Texture mapping units and Render Output Pipelines all run at 743MHz
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The more stream processors you have the more Shader Operations you have
The more Texture mapping units you have , more Texture Fill Rate you have
The more Render Output Pipelines you have, the more pixel Fill Rate you have
I hope that it is clear for you