7900GT and 7900GTX in the SLI mode
Acknowledgements
The editorial board appreciates Meijin for the GeForce 7900GT/GTX video cards presented for tests.
Preface
We already got acquainted with NVIDIA's latest video cards - 7900GT and 7900GTX, but that time no word was spoken about performance of these cards when operated in combination, that is, in the SLI mode. Today, we are rectifying this error and are introducing you, dear readers, to the data on performance of NVIDIA's novelties in the combined performance mode.
I hope our permanent readers guessed that the news "SLI performance attaining 97%!" was a 1st April joke. The described methodology for plugging in a second video card using a piece of polyethylene was no more than fantasy. In fact, such a high speed boost gained from merging two video cards is not yet encountered in reality. Nevertheless, "every joke has merely a portion of joke, the remaining part is truth". The speed boost gained from plugging in a second video card is there - it is even more than noticeable. But - all in good time.
Our test configuration is very well known to you. This time it hasn't undergone any changes. Due to that we can make an adequate comparison of operation results for single 7900GT and 7900GTX video cards versus the same in the SLI mode.
Test setup
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WinXP + SP2 + DirectX 9.0c
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NVIDIA video cards were tested with NVIDIA version 84.20 drivers.
This is how our test bench looks with the two 7900GTX video cards fitted in place.
Preliminary Notes
Unfortunately, for now we can't run tests of two latest video cards in the CrossFire mode. So, to make a comparison versus the results for GeForce 7900GT/GTX in the SLI mode, we made use of the results available at our disposal. Certainly, such a comparison is not quite correct - it would be correct to test X1900 CrossFire with the latest drivers. Nevertheless, I presume we can use these results as approximate estimate for X1900 CrossFire acceptable enough.
All the tests were run without overclocking. That is, the video cards were running in the nominal modes. As regards testing in the SLI mode, in one of the test series we wanted to depart from canons somehow and find out how SLI-enabled video cards operate without using a V-Link bridge (which is put on top of the video card). Such operation is allowed by the latest ForceWare drivers albeit a warning is displayed saying that the SLI performance without the V-Link bridge will be lower than expected. That is indeed so. But how lower - we'll see from the tests.
Benchmarking
The diagrams are built in a way that the absolute value in "marks" or FPS are shown in the middle of the results bar. To the right of the bar, there is a percentage of performance change for the SLI combination versus a similar but single video card. That is, for 7900GTX-SLI displayed is the percentage of boost versus a similar single 7900GTX video card. For 7900GT-SLI - as compared to the single 7900GT, and finally for X1900 CF - boost percentage versus the single X1900XTX. We should be aware regarding the latter comparative pair X1900CF/X1900XTX that their operating frequencies are somehow different. X1900 CrossFire Edition offers operating frequencies of GPU/memory which are somehow lower than in X1900XTX, so the overall performance boost produced from merging X1900 CF Edition + X1900XTX is less than it could be with two X1900XTX at the nominal frequencies.
Let's start with the synthetic benchmarks.
We see that the results for 7900GTX-SLI at 3DMark'06 are practically identical as those for X1900CF, which is evidently caused by the CPU performance. Interestingly, the lack of the V-Link bridge does not strongly affect the results in the SLI mode.
Despite that 3DMark'05 is more "favorable" to ATI's video cards, the CrossFire combination here loses to 7900GTX-SLI. And again - the lack of the V-Link does not affect in any way the performance of video cards in the SLI mode. As regards the pure boost, then the "weaker" video card will offer higher boost if the results are CPU-bounded. That is what we see on the example of 7900GT-SLI.
3DMark'03, because of its venerable age, is more sensitive to the "pure speed" of the GPU and is highly responsive to merging two video cards. At this test, NVIDIA video cards have been traditional leaders, and this time the situation hasn't changed. However, it is interesting that the boost for X1900 in CrossFire is a little bit higher than for 7900GTX-SLI. At the same time, the maximum boost - over 60% - is of course attained on 7900GT-SLI.
As we can see, all is remarkable at the synthetic benchmarks, but what will the games show? OK. Going on.
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