Video Card Specs -- what to look for?
Generally, the biggest factor that determines the performance of a video card is the amount of shaders. But the number itself will not tell you everything, because modern Nvidia cards have scalar processors which work with one data element at a time, while Ati cards have 5-component processors that work with 5 elements at a time. Moreover, Nvidia has their shader units clocked at about 2x the clock frequency of the rest of the gpu, while Ati uses a single clock domain. In addition, Ati's shaders are more sensitive to driver optimizations to extract the most parallelism out of the code. So, the bottom line is the spec numbers aren't a reliable way of comparing video cards anymore, and your best choice is just to look at published benchmarks to determine the overall performance level of new video cards.
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