You need to support Shader model 4.0 to get the stamp of Direct X 10 and that's about it, but this doesn't necessarily mean your Shaders have to be unified.
This confirms Nvidia's theory that you don't need unified shaders, at least for the time being. If the Vole doesn't care about it, why should Nvidia? The big green company decided to do the different approach as its Vertex, Pixel and Geometry Shaders will still be divided in at last two separate function parts and we believe that this will give some additional speed in DirectX 9 games.
That is how Nvidia plans to make its G80 chip and Microsoft doesn't object. Nvidia will be first to launch a DirectX 10 part with ATI to follow roughly two months after Nvidia introduces its G80 baby. µ
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