If you have been following the news, some very strange things are going on with the nVidia nForce4 chipsets. About six weeks ago, MSI showed an nForce4 ULTRA motherboard with a regular x16 PCIe slot, plus an open-ended x4 PCIe slot. Those who saw the demos said that MSI was running two matched video cards in what they called a "semi-SLI mode", which ran at about 90% of the performance of normal nVidia SLI. This was an interesting development because nF4 Ultra chipsets are cheaper than nF4 SLI chipsets. The boards based on the Ultra chipset are, therefore, much cheaper than the high-end SLI parts that we are seeing in the market. An arrangement like this would be a god-send for computer enthusiasts who watch their budget, yet still like to enjoy most of the benefits of SLI dual video-card performance.

Just as quickly, we learned that nVidia was not happy with this "SLI hack" and they changed their drivers quickly so that "semi-SLI would not work with current and later Forceware drivers." It appears that the later Forceware drivers check the chipset ID and if the driver sees "Ultra", then SLI is not enabled. MSI decided to kill the "semi-SLI" board because it would be a nightmare supporting a board that would only run with older nVidia SLI drivers.

Then, at CES, DFI was displaying both nForce4 SLI and nForce4 Ultra motherboards with two x16 PCIe slots. We were told that Epox also had an nForce4 Ultra motherboard with another semi-SLI solution based on the cheaper Ultra chipset. DFI told us that they used the same PCB for both versions of the nForce4 boards for economy, and that in fact, the nForce4 Ultra board could run a dual x2 video mode with earlier nVidia Forceware drivers in addition to standard single x16 video mode. Given AnandTech's close working relationship with DFI, we had arranged an exclusive look at both DFI boards. When the boards arrived, we were indeed able to run an x16/x2 dual video mode on the nForce4 Ultra with driver version 66.75 - a very early nVidia SLI driver. We tried many, many Forceware versions and also found that 70.41 also worked by adding one line to the registry. However, like MSI, the Ultra dual-video only worked on very old SLI drivers or on drivers with a Registry mod.

It was clear at this point that this Ultra dual-video solution did work, but that nVidia had turned it off in recent drivers. This caused us to wonder what was really going on with nForce4 chipsets. If nVidia could enable/disable this Ultra SLI in drivers, then the base chips must be very, very similar. In fact, it would be logical if the nF4 Ultra and nF4 SLI were exactly the same chip with some modification, making the chip an Ultra in one case and an SLI in another. The pin-out configurations are, after all, exactly the same with both chipsets.

It was with this idea that we took a closer look into the possibilities, and what we found will surprise you! It turns out that the nForce4 Ultra is apparently just an nForce4 SLI with SLI turned off. What is even more important is that we also found a way to turn on the disabled SLI!

Breaking the SLI "Code"
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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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