PCI Express Interface Performance

Although the high end NV4x series didn't implement a PCI Express interface at the high end, the mainstream and entry level boards did, however G70 will represent a second generation of PCI Express for NVIDIA so we can take a look at the performance to see if there have been any changes.

For the first test we'll take a look at TexBench, using up to 100 textures at 1024x1024 which requires 400MB of texture space, greater than the local frame buffer space on the boards here so that some texture information will need to be addressed from system RAM.

Tex Bench Texture Size Download (MB/s) 64x64 128x128 256x256 512x512 1024x1024
7800 GTX 332.5 500.0 516.5 441.3 18.6
6800 Ultra 339.7 500.0 470.8 438.4 21.7

64x64 128x128 256x256 512x512 1024x1024
7800 GTX % Faster than 6800 Ultra -2.1% 0.0% 9.7% 0.7% -14.0%

The results are somewhat variable here, so its difficult to spot a trend, other than to say that where most texture information is going to be drawn from system RAM the 6800 Ultra has the higher download performance.

The Serious Magic test renders an image then reads that back from the graphics chip to the system, we can assess the upstream PCI Express performance

Serious Magic Image Download (MB/s) 640x480 800x600 1024x768 1280x1024 1600x1200
7800 GTX 646.0 652.0 653.0 663.0 665.0
6800 Ultra 628.0 638.0 642.0 653.0 656.0

640x480 800x600 1024x768 1280x1024 1600x1200
7800 GTX % Faster than 6800 Ultra 2.9% 2.2% 1.7% 1.5% 1.4%

This test shows a slightly more consistent result with the 7800 GTX displaying a slightly greater upload performance then the 6800 Ultra.