X-bit labs

The Fast and Furious: ATI Radeon X1900 XTX Review (page 11)

Category: Video

by Anton Shilov , Alexey Stepin

[ 01/24/2006 | 08:28 PM ]

There is hardly a point to talk about performance in pixel shaders 1.1 where memory bandwidth and cache efficiency play the most significant roles today. This is the last time when we publish high-end GPU results in pixel shader 1.1 test from the 3DMark 2001 SE which was released slightly less than 5 years ago.

In case of pixel shaders 1.4 the GeForce 7800 GTX 512 has the considerable lead over the Radeon X1900 XTX, but the framerate is so high that nobody is likely to see any difference.

The pixel shader 2.0 test from the 3DMark03 package contains neither high-resolution textures nor tough pixel shaders. We cannot explain why the Radeon X1900 XTX is outperformed by the GeForce 7800 GTX 512 by about 100%, nor can ATI.

Pixel shader 2.0 test from the 3DMark05 and 3DMark06 benchmarks shows a light moving on the rough surface. Generally speaking, the test is not mathematically heavy, but it is dependant on texture fetches, thus, on memory bandwidth.

The Radeon X1900 XTX is virtually two times faster compared to the Radeon X1800 XT, but the GeForce 7800 GTX 512 manages to come to the leader very close.

Surprisingly, the same shader from the 3DMark06 package performs differently compared to the case of the 3DMark05.

The Perlin Noise pixel shader 3.0 test of the 3DMark06 computes six octaves of 3-dimensional Perlin simplex noise using a combination of arithmetic instructions and texture lookups. The pixel shader used in this test consists of a total of 48 texture lookups and 447 arithmetic instructions, resulting in a total of 495 instructions and around 9:1 ratio of arithmetic instructions to texture instructions. All texture lookups are made into a single 32 bit 256x256 texture (64KB), which keeps the memory bandwidth requirement reasonably low despite the large number of lookups.

Needless to say that the amount of the arithmetic instructions means that the graphics card with the highest math power will claim performance lead.  Judging by the results memory bandwidth still influences the benchmark results, however, it is obvious that 48 pixel shader processors allow the Radeon X1900 XTX to leave the GeForce 7800 GTX 512 far behind, while the latter leaves the Radeon X1800 XT in the dust because of higher amount of pixel processors and higher memory bandwidth.