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Pixel Pipelines: Fillrate, Pixel Shaders

As usual we will begin with the polygon fillrate. The first test is the Fill Rate test from 3DMark2001 SE package. The test displays 64 semi-transparent surfaces wit one texture on each:

To estimate the efficiency of caching systems and the efficiency of frame buffer and Z-buffer compression, we forced FSAA 2x and 4x during the tests.

The results show that ATI RADEON 9700 Pro and RADEON 9800 Pro do not react so strongly to the enabled full-screen anti-aliasing as NVIDIA GeForce FX 5800 Ultra and 5900 Ultra.

To draw each pixel the chips have to read the old color value from the frame buffer and write the new one into it. Of course, the situation may change in real applications, but in this synthetic benchmark ATI chips appeared better prepared.

Another interesting observation: despite lower core frequency, NVIDIA GeForce FX 5900 Ultra proves faster than GeForce FX 5800 Ultra. It should be the enhanced caching algorithms and higher memory bus bandwidth that help NVIDIA GeForce FX 5900 Ultra to beat the predecessor here.

During multi-texturing NVIDIA chips show higher results due to their ability to lay two textures per clock. ATI RADEON 9700 Pro and RADEON 9800 Pro feature 8 pixel pipelines but both of them need an extra clock to lay each texture. As a result, all four chips appear in equal conditions: in this benchmark they lay maximum 8 textures per single surface. NVIDIA chips using 4 pixel “pipelines” configuration process 4 pixels every 4 clocks, while 8-pipeline chips from ATI – 8 pixels every 8 clocks. In the long run, NVIDIA GeForce FX 5900 Ultra and NVIDIA GeForce FX 5800 Ultra win here due to their higher clock frequencies: 450MHz and 500MHz against 380MHz and 325MHz respectively.

Here the memory bus is not loaded too much, because the chips lay not one but 8 textures over a single semi-transparent surface that is why the frame buffer values should be read/written 8 times more rarely. As a result, higher working frequency of NV30 compared with NV35 played a crucial role here and NVIDIA GeForce FX 5800 Ultra outperformed the newcomer.

The next test displays a polygon “covering” the entire screen. There are from 0 (no texture, pixel color is obtained as an interpolation of polygon vertex colors) to 4 textures sized as 512x512 superposed over this polygon. This benchmark allows estimating which pixel “pipelines” configuration NVIDIA chips use in every case:

Both: GeForce FX 5800 Ultra and GeForce FX 5900 Ultra behave the same way: as graphics accelerators using 4 classical pixel pipelines with 2 TMUs per each.

It is remarkable that higher core frequency of GeForce FX 5800 Ultra allows it to outpace the newcomer only when there are no textures to be laid. In all other cases enhanced caches help NV35 to beat the predecessor.

Now let’s move to the most exciting part of this section: pixel shaders performance. First comes Pixel Shader Speed test from 3Dmark2001 SE package:

NVIDIA GeForce FX 5900 Ultra is faster than the predecessor here, however, there are no pixel processor enhancements to thank for that: the card owes its victory to higher memory bus bandwidth and more efficient caches.

The situation remains unchanged even with a more complex pixel shader: NVIDIA GeForce FX 5900 Ultra is slightly ahead of NVIDIA GeForce FX 5800 Ultra.

However, if ATI graphics cards were just a little ahead of NVIDIA’s competitors in the first test, then here RADEON 9800 Pro and RADEON 9700 Pro are much farther ahead. This situation has already been describe in our NVIDIA GeForce FX 5800 Ultra Review.

So, the DirectX8 Pixel Shaders performance tested with 3DMark2001 SE do not indicate that there have been any changes made to the integer unit of the NV35 pixel processor compared with NV30.

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