@princeton Graphics are generally made up by vertices and pixels. Both should be shaded by the graphics chip, with two different mechanisms. These are the vertex pipelines and the pixel pipelines. The operation of these pipelines is controlled by both hardware and software. Regarding the software layer, the possibility to use a common or unified layer to control both vertex and pixel pipelines is feasible. ATI adopted the Unified-Shader architecture in the development of the Xbox 360 GPU, and the stuck with it all later incarnations of Radeon Series. According to the Unified-Shader concept, no distinct dedicated vertex and pixel shader engines are used (which is the case with nVidia). Instead these are replaced by an array of Unified-Shader engines able to execute both kinds of instructions. ATI’s modern architecture lies around big fat units and lot of tiny ones (80+720 in case of Radeon 4800 series), and the clock is much lower than in case with GeForce cards. At the same time, Nvidia went the other route and came up with large number of “fat” units. ATI believes that such an approach offers the best performance and also better allocation of the GPU resources, compared to NVIDIA’s dual shaders. NVIDIA’s answer to these claims is that the Unified-Shader technology could be also a future option for the company, as long as it will be assured that its operation will be smooth, easily controlled and predictable. These two technologies are simply incomparable, as sometimes ATI’s architecture wins while sometimes Nvidia wins; but this differs from case to case.