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ATI RADEON HD 4870 X2 2x1024MB

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DX10: Vertex texture fetch rate

Vertex Texture Fetch tests measure the speed of many vertex texture fetches. These tests are essentially similar, and the correlation of their results in Earth and Waves tests must also be similar. Both tests use displacement mapping based on texture fetches. The only major difference is that the Waves test uses conditional branches, while the Earth test does not.

Let's analyze the first test (Earth) in Effect detail Low mode:

Judging by our previous reviews, this test is affected not only by texturing speed, but also by ROP performance and memory bandwidth -- the easier the mode, the stronger their effect on performance. The dual-GPU card from the RADEON HD 4800 family is the leader in all modes. But, it's apparently affected by memory bandwidth, which limits performance, especially in the Low mode. Multi-GPU rendering is also doing well. Let's have a look at results of this test with more texture lookups:

The situation hasn't changed much, but texturing affects performance to a higher degree, judging by previous tests. Dual-GPU rendering is still highly efficient. So even though HD 4870 is outperformed by NVIDIA solutions, HD 4870 X2 is still the leader. Both GeForces come close to it in Low modes, as performance is limited by memory bandwidth in this case.

Let's have a look at results of the second vertex texture fetch test. The Waves test executes fewer texture lookups, but it uses conditional branches. The number of bilinear texture lookups in this case reaches 14 (Effect detail Low) or 24 (Effect detail High) per each vertex. Geometry complexity changes just like in the previous test.

The second test, Waves, is disposed to AMD products better, new RADEON HD 4800 cards look very good here. The single-GPU card performs on a par with the dual-GPU predecessor, outperforming NVIDIA cards, except for the simplest mode affected by memory bandwidth. And the dual-GPU card is a perfect leader in this test. It seems that TMUs in RV770 are more efficient than those in GT200 in these conditions. Let's analyze the second modification of the test:

Almost the same situation again. Although AMD cards improve their results versus NVIDIA cards as test complexity grows, the latter lose more speed to the new test conditions. HD 4870 X2 is the leader in all modes, it's almost twice as fast as its single-GPU modification (HD 4870). By the way, the latter is the best single-GPU solution.

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