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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  • Wesley Fink - Tuesday, January 18, 2005 - link

    #40 and #44 -
    When the pads are closed on the nF4 Ultra chipset the chipset is then identified as SLI by the system and OS and performs the same as SLI. The x8/x8 is the nVidia defined SLI mode that works after the mod. The board can also - in addition - perform in x16/x2 mode.
  • icarus4586 - Tuesday, January 18, 2005 - link

    When the Ultra is modded to by closing the resistor pads, can it function in 8x/8x mode? At some points in this review I wasn't sure whether the modification allowed 8x/8x or just 16x/2x. Will 8x/8x work on a modified Ultra motherboard, as long as (like DFI's) it has 2 full length slots?
  • KristopherKubicki - Tuesday, January 18, 2005 - link

    Googer: Wesley is correct. The MSI "DBS" board had an open ended 4 lane slot with a full 16 lane slot. The DFI board runs on two 2 lane slots.

  • archcommus87 - Tuesday, January 18, 2005 - link

    Does even a simple pencil mod like this void any warranty on any board?
  • Cygni - Tuesday, January 18, 2005 - link

    I honestly dont really see the point of the Ultra to SLI conversion. You are now paying an extra $400+ dollars for the second video card for 50% over the performance of one video card... it doesnt make sense. The 8x/8x SLI made the performance for the expendature much more attractive.

    The whole process of changing the Ultra to SLI is very cool, however, haha. Personally, I still see the extra $100 for a true SLI as worth it when you are already shelling out $800 for video cards (assuming 6800U's).
  • Zebo - Tuesday, January 18, 2005 - link

    I just don't see the attraction. It's slower obviously and anyone doing sli can afford a non-hacked solution like real live sli.

    Right now you can get SLI boards for $200. Thats insignifigant premium compared to two GT's @$500 a each. And especially after this flood of new boards price will come down on the real sli boards.

  • bob661 - Tuesday, January 18, 2005 - link

    I said "cheaper" not cheap. Maybe you need to bone up on your reading comprehension skills.
  • Crassus - Tuesday, January 18, 2005 - link

    Wesley, thank you for following up on my comment.
  • Googer - Tuesday, January 18, 2005 - link

    By the way SLI offers a poor price to performance ratio, IN some games the performance is 10-15% or less and in others there is none. A single 6800ultra
    can beat a 6600 sli setup in MOST games.
  • Googer - Tuesday, January 18, 2005 - link

    Wesley are you sure it was MSI that had the x4 slot and an sli mode for the nFORCE4 ultra, because that discriptrion sounds more like DFI than any MSI beta board that I have seen lately.

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