Ive been thinking about the radical changes coming with DX10 and shader model 4.0. I think that in the long run, this is a good paradigm shift. In the short run though, I get the feeling that the first wave of DX10 video cards will be slower running DX9 code. My reasoning is that the DX10 architecture essentially calls for a fully progammable GPU that runs shader language code and gives the developer complete control of the pipeline. Basically, the rendering process becomes software running on the GPU. The legacy approach under DX9 was dedicated texturing and shader modules directly addressed via a scheduler. For this DX9 code to run on DX10 video hardware, presumably some sort of legacy compatibility virtualization layer will have to run on the DX10 GPU and emulate the presence of some number of dedicated units. The question will be will the first wave of DX10 GPUs have the horsepower to run DX9 in emulation mode faster than the final wave of ultra performance DX9 engines? My guess is no.
UPDATE: My guess was incredibly wrong! And I’m happy about it! (here running dual 8800GTX cards in SLI) Nvidia really created a barn burner with the 8800 and ensured that not only is it the first DX10 card, but it is also UNQUESTIONABLY the performance king in DX9. Kudos to NVidia for bringing out a part that, while expensive, really delivers. ATI, unfortunately, still struggles with the R600 even today.
UPDATE2: My guess was actually not SO wrong! And I’m not happy about it =( The compatibility problems and driver issues that continue to plague the G80 series are becoming legendary. Just do a search for G80 and stuttering or G80 and "texture problems" to see what I mean. Unfortunately, it looks like the transition from dedicated texture/shader units to a programmable stream processor model is actually not going so smoothly. Worse yet is that NVidias "fix" is looking more and more to be like the G90 (and I have my doubts there as well). I suspect the only *real* fix will be time and game devs migrating to native DX10. This will go down as another of those periods where transition to new tech was painful. Ouch.