X-bit labs

NVIDIA GeForce 7800 GTX: New Architecture Exposed (page 13)

Category: Video

by Alexey Stepin

[ 06/22/2005 | 12:52 PM ]

Pixel Shader Performance

Marko Dolenc’s Fillrate Taster can also benchmark the performance of a graphics processor with pixel shaders of versions 1.1 and 2.0:

NVIDIA has really managed to achieve a considerable increase in the pixel shader performance. The G70 is about 1.5 times faster than the NV40 with complex pixel shaders that create per-pixel lighting. The gap becomes even wider on simpler shaders, yet does not become twofold. The RADEON X850 XT Platinum Edition outperforms the GeForce 6800 Ultra on simple shaders but the GeForce 7800 GTX with its 24 pixel processors gives no chance to the ATI card. Note also that even the new pixel processors from NVIDIA profit from using the half precision in version 2.0 pixel shaders.

The situation doesn’t change when we disable Z writes.

We get a most curious picture after we disable color writes: the GeForce 7800 GTX is more than 1.5 times faster than the GeForce 6800 on complex pixel shaders, but the gap is much smaller with simple shaders. This must be due to the architectural features of the GeForce 7800 GTX which has 24 pixel processors, but only 16 ROP units.

So, the new graphics processor from NVIDIA shows its best qualities in doing complex mathematical commutations, and shaders that create per-pixel lighting are exactly an example of such a task.

The GeForce 7800 GTX crunches through complex pixel shaders at a tremendous speed as the results of the shader performance section of the new version of Xbitmark confirm. As expected, the new graphics card enjoys a big advantage over its opponents in subtests that involve complex mathematical computations: in the shaders Dot Product Bump Mapping + Specular + Reflection, Factored BRDF + HDR, Metal + Phong, Wood and especially in both Dynamic Branching. The latter two are very difficult since they consist of more than 170 instructions, but the GeForce 7800 GTX maintains a frame rate above 90fps even on these shaders. By the way, these two shaders and NPR hatch 10textures PS3 are written in Model 3.0, so they don’t launch on ATI’s cards.

The advantage of the GeForce 7800 GTX over the GeForce 6800 Ultra is smaller on textures-heavy shaders like Cook Torrance + Texture + Fresnel or 27-Pass Fur, which is performed in 27 passes as its name suggests. This is the consequence of having 16 ROP units and 24 pixel processors. Anyway, the overall performance of the new product from NVIDIA is very high, and it is really the fastest consumer graphics card today.

This test is not the most complex possible. It uses only version 1.1 pixel shaders. The results of the two GeForces differ much only in 1600x1200 resolution.

The pixel shaders from the Advanced Pixel Shader test are more complex and the GeForce 7800 GTX is 1.5 times faster than its opponents here.

The GeForce 7800 GTX enjoys an even greater advantage over the previous-generation solutions in the analogous test from 3DMark03: up to 100% more speed in high resolutions! NVIDIA’s claims about a twofold advantage of the GeForce 7800 GTX at executing pixel shaders seems to be true to life.

The advantage of NVIDIA’s new architecture is also conspicuous in 3DMark05, in all resolutions. The pixel shaders from this test are mathematically difficult, but it is here that the G70 shows its best qualities.