Performance in Theoretical Tests

Having a higher GPU clock rate, the GeForce 7900 GTX has a higher scene fill rate than the GeForce 7800 GTX 512. We can’t see any anomalies in the new card’s behavior even though the new GPU has got slimmer by 25 million transistors in comparison with the older one. Nvidia’s solution now boasts a higher fill rate than the Radeon X1900 XTX even without texture mapping.

The same is true for the second test which measures the pixel processors performance. The GeForce 7900 GTX behaves identically to the GeForce 7800 GTX 512, the GPU frequency accounting for the difference in their results.

Xbitmark provides us with more detailed results. You can see that the core frequency increase from 550 to 650MHz has a very positive effect on the performance of the GeForce 7900 GTX at executing various pixel shaders. Having two times fewer pixel processors, Nvidia’s new GPU is at least no worse than the Radeon X1900 XTX even when running math1ematics-heavy shaders like Dot Product Bump Mapping + Specular + Reflection, Factored BRDF + HDR or Wood. Some of the pixel processors of the Radeon X1900 XTX must be just idle in Xbitmark because the scenes of this test use no more than 3-5 shaders at a time. As we know already, a GPU with a lot of pixel processors can only show its best when there are multiple math1ematics-heavy shaders to be performed simultaneously.

Having 24 TMUs, the GeForce 7900 GTX enjoys a bigger advantage in tests with pixel shaders that include multiple texture lookups (both the NPR Hatch shaders and Cook-Torrance + Freshnel). The only area ATI’s architecture remains unbeaten in is execution of shaders with dynamic branching. The Radeon X1900 XTX still has no rivals there.

All in all, the GeForce 7900 GTX does somewhat better than the Radeon X1900 XTX. The two graphics cards are roughly equivalent when it comes to executing pixel shaders, but Nvidia’s new solution is better than the senior Radeon at processing textures. The latter is indeed better on shaders with dynamic branching, but such shaders aren’t yet used in games.

And now it’s time to see how well the new family of graphics cards from Nvidia is going to do in real-life conditions that often have very little to do with theory.