Performance: x16 vs. x16/x2 vs. x8/x8 (SLI)

The best way to verify the success of the mod was to run benchmarks. We had already done extensive testing of SLI performance in Anand's NVIDIA's GeForce 6 SLI: Demolishing Performance Barriers. To get right to the point, we tested the Ultra modded to SLI with Half Life 2, Doom 3, and Far Cry at both 1280x1024 and 1600x1200. We also benchmarked at both settings with and without the eye candy - since Anti-Aliasing and Anisotropic Filtering can exact a large hit on a single GPU.

We were interested to see exactly what performance you could get with two video cards on the Ultra board before the mod to SLI, so we also ran benchmarks of the performance of x16/X2 Ultra dual-video card mode.

All tests were run on a DFI LANParty UT nF4 Ultra-D and a DFI LANParty nF4 SLI-DR. We first confirmed that test results were the same on the LANParty UT modified to SLI and the LANParty nF4 SLI, which is a native SLI chipset board. There was no difference in performance after the SLI modification to the Ultra chipset, so results are reported as SLI and relevant to either SLI or Ultra modified to SLI.

Video cards were a single MSI 6800 Ultra PCIe or a matched pair of MSI 6800 Ultra in SLI and x16/x2 modes. Memory in all benchmarks was OCZ 3200 Platinum Rev. 2 (Samsung TCCD) at 2-2-2-10 timings. The CPU was an Athlon 64 4000+, and the power supply was an OCZ PowerStream 600.

In the course of testing, we found that we could actually run the x16/x2 mode on either the SLI board or the Ultra board by leaving the jumpers in normal mode, using an SLI bridge across the two video cards, and enabling SLI in the nVidia driver. Results on the SLI board in x16/x2 mode were, as expected, the same on the nF4 Ultra board as shipped or the Ultra after SLI modification. The one huge advantage of the SLI-mod was that once we had SLI-modded the Ultra chip, we could run x16/x2 mode with any nVidia Forceware driver up to 70.xx. The 70.90 driver was the highest driver to support x16/x2 mode even with an SLI chip. x16/x2 would not run, however, with the most recent 71.xx drivers. 71.xx drivers report the board to be SLI-capable, but it does not recognize the second card as an appropriate card for SLI. Clearly, nVidia must have turned off x16/x2 support in the most recent driver as well, only allowing their specified x8/x8 mode to work. We suspect that enthusiasts will find a way to correct this very quickly.

UPDATE: The Gigabyte 3D1 is a single video card with two 6600GT GPUs. It will only work in x8/x8 (nVidia) SLI mode on a Gigabyte SLI board. However, we did find the 3D1 will operate in x16/x2 mode on both DFI boards with jumpers in "normal" position. We have added test results to our charts with both single 6600GT and x16/x2 dual video mode with the 3D1. The Gigabyte 3D1 provides the interesting possibility of a form of SLI performance on single x16-slot Ultra boards with the SLI mod.

Breaking the SLI "Code" Half Life 2: x16 vs. x16/x2 vs. x8/x8 (nVidia SLI)
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  • HystericPoison - Thursday, October 13, 2005 - link

    i did the mod last night. it took me 2 tries, because i guess on the newer boards they have a dot of glue over the resistors that i had to scrape off with a knife. a dot of conductive pen (purchased at radio shack for $13 and change) was all it took.
  • rancidmonkey - Saturday, February 26, 2005 - link

    This is my first post to Anandtech. :) I have ordered a DFI LanParty NF4 Ultra-D from Newegg, and this "SLI-enable" mod is exciting, mostly because of the "budget-minded gamer future upgrade" benefit mentioned by a couple others here. However, what do you all think of possible compatibility issues arising from attempting to pair a 6600GT purchased this month with one purchased 10 or 11 months from now? Could imperceptible changes in the manufacturing process make two seemingly identical cards not work together in SLI mode? I suppose if you really are budget-minded, you could scour ebay for a second-hand card purchased around the same time as yours.
    What do you think?
  • cyburzaki - Thursday, February 24, 2005 - link

    please forgive me if my above comment about PCCaseGear and the bridge was already covered here. I am in a rush and only read the last fourth of posts...
  • cyburzaki - Thursday, February 24, 2005 - link

    DFI sized bridges are definitely being made by at least one third-party, since PCCaseGear in Australia includes with their Ultra-D boards an SLI bridge. But I emailed them and asked them the name of the German company that makes them, and they refused to tell me.
  • cyburzaki - Thursday, February 24, 2005 - link

  • LX - Friday, February 11, 2005 - link

    Wesley (or anyone else, for that matter),

    Where can one get the SLI bridge to use with this mod?

    Thank you!
  • ImJacksAmygdala - Monday, January 24, 2005 - link

    I bet it is easier to get the SLI bridge for this mod than it is to get an Nforce4 Ultra to try it.
  • Wesley Fink - Saturday, January 22, 2005 - link

    #77 - DFI tells us all boards that will reach the retail market will have the modifications we are expecting. There is a new BIOS and several updates of components to improve performance and memory compatability. These changes have been made to production boards and the first boards off the line are also being updated post-production before release to the retail market.
  • ChineseDemocracyGNR - Saturday, January 22, 2005 - link

    By post-production modifications, do you mean that the first boards to hit the market will not have these improvements?
  • Wesley Fink - Saturday, January 22, 2005 - link

    ALL -
    As a result of feedback to DFI on the initial testing, DFI is making a few post-production modifications to the board and BIOS to further improve memory compatability and overclocking. There is nothing wrong with current overclocking performance, but we want to bring you a review of the final production board, so we are waiting for the boards with modifiactaions to arrive. Those are expected by the middle of next week. We should have a review of both the DFI boards around the end of next week unless there are further delays.

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