We were expecting a reaction from ATI in response to the release of the GeForce 7800 GTX, but NVIDIA made the next move with a new high end graphic card, the GeForce 7800 GT.
The GeForce 7800 GT is based on a G70 chip (same as the 7800 GTX), but with one quad engine (4 pixel shader pipelines) and a vertex engine deactivated. Frequencies are also slightly lower at 430 instead of 600 MHz.
You probably noticed the GPU frequency in quotation marks and there is a reason for that. We didn’t see it in June in the first GeForce 7800 GTX test, but the GeForce 7800 uses quite a complex frequency system. Two different parts of the CPU use different frequencies, one close to the announced figure (but not identical) for pixel shader pipelines and ROPs and a much higher one for the other parts, mainly vertex shaders.
For NVIDIA the release of the 7800 GT is the opportunity to reorganise their high end graphic cards and the GeForce 6800 Ultra will become of lesser interest and eventually disappear. Official prices of the GeForce 6800 GT and 6800 are lower and this corresponds more or less to price cuts applied in June. So, the price of the GeForce 7800 GT should be around $400, $299 for 6800 GT and $199 for 6800.
CineFX 4.0: gains in practice
Overall the GeForce 6800 and 7800 feature quite similar functions: Shader Model 3.0, HDR FP16, and SLI. The power of three as seen by NVIDIA.
We already described in detail the GPU architecture in the 7800 GTX test,
here. We only remind you that with the GeForce 7800, NVIDIA has slightly optimised CineFX architecture to increase efficiency, related to an increase in IPC (number of instructions processed per cycle). This improvement is difficult to measure as it varies from 0 to 100%. We estimate that it’s generally from 5 to 20% and much more in very specific cases. We tried to verify this with the comparison of a 16 pipe GeForce 7800 and a GeForce 6800 GT clocked at the same frequency. The GeForce 7800 with 16 active pipes was clocked at "346 MHz", 351 MHz for pixel shaders and ROPs and 387 MHz for vertex shaders. This difference in vertex shading has no influence on games as they are rarely restricted on this level, and so the comparison is valid.
There are indeed performance gains and they are due to several NVIDIA optimisations. First, antialiasing and anisotropic filtering efficiency have improved (unfortunately with a slightly lower quality for the latter) with performance gains from 6 to 33%.
For Doom3, the gain is almost 30% in 1920x1200, showing an optimisation in management of high resolutions. Some optimisations, which are meant to avoid useless calculations have an integration cost directly related to the higher resolution they accelerate. With the 7800, NVIDIA extended some of these optimisations beyond 1600x1200, which explains this type of gain.
The HDR mode is still costly to performance, but is slightly more efficient with the 7800. The gain due to the architecture is 16% in Farcry.
Finally, you will see that there has been an amazing progression in performance in Colin McRae 05. It’s hard to explain and is probably due more to a software optimisation rather than architectural modifications.
