The more significant changes have to do with the pixel pipeline. Just as with the R8500, the R9000 has four pixel pipelines. Instead of two pixels per cycle, however, these can only calculate 1 texel per cycle. In exchange, the number of textures that comprise the end pixel increases from three to six. What these confusing numbers mean in practice is that the R9000 is considerably slower than the R8500 in games with multitexturing.
The second change has to do with the vertex shader. It wasn't till now that ATI has admitted that the Radeon 8500 contains two vertex shader units, similar to the GeForce4 Ti. The reason for keeping quiet on this was more because of marketing concerns rather than understatement. The R8500 had two shader units more than NVIDIA's GeForce3. With the R9000, these units were re-worked and optimized. If the Canadian PR department is to be believed, then the new vertex shaders contain many optimizations that are also found in the R300 design.
The third and final big change affects the video capabilities. Graphics cards from ATI have the reputation of providing high quality DVD and video playback, and with good reason. As with the R300, ATI does away completely with the circuitry responsible for this and instead uses a new technology called "Videoshader". This allows ATI to combine the optimized calculations in the hardware and the flexibility of a software solution, in the form of special pixel shader programs. During video playback, the pixel shaders remain in 2D mode anyway, so they are available for this purpose. In addition, there are completely new realtime filtering capabilities available that, for example, prevent pixelation in low-resolution videos or allow special optimizations for specific video codecs such as DivX. With simple driver updates, optimizations for new video formats can be implemented. This step lets ATI save on transistors, which, in turn, has a positive effect on the price. However, it still remains to be seen how this solution works in practice.
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With the Radeon 9000 series, ATI offers a very solid 3D performance to a reasonable price, and it also takes the technological lead in the mainstream segment ($100 - $150). It remains to be seen whether NVIDIA will soon be able to hold its own with its GF4 MX (NV17) successor NV18, which stands ready at the starting line. The solution from SiS, whose pixel shader support is supposed to allow it to keep up with the competition, at least on paper, disqualifies itself in practice through the poor performance of the pixel shader unit.
