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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  • Klaasman - Tuesday, January 18, 2005 - link

    What would be sweet is TWO Gigabyte 3D1 for a total of four GPU's.
  • mclearn - Tuesday, January 18, 2005 - link

    Are there any visible differences in the DFI Ultra and SLI boards? Maybe the fix for this is as simple as the chipset's "upgrade"
  • Deucer - Tuesday, January 18, 2005 - link

  • cnq - Tuesday, January 18, 2005 - link

    Nice article, and thanks for switching your SLI measurements to 12x10 & 16x12 (I savaged you for including 10x7 in a prev review, which probably no SLI user will both with).

    One suggestion for future FarCry runs on SLI: please try with the magnificent eye candy setting "HDR" enabled (new with FC v1.3). It looks great, but is a graphics card crippler -- and thus the **perfect** test for a 2x6800U SLI system.
  • Wesley Fink - Tuesday, January 18, 2005 - link

    Unfortunately the Gigabyte 3D1 dual-gpu 6600GT does NOT work on the DFI when trhe jumpers are switched to SLI mode. The nVidia driver sees that the system is SLI-capble, but it does not recognize the 2nd GPU as there for SLI. This is true with 66.93, 70.90 and 71.40 drivers. If the Gigabyte single-slot dual-GPU would work with more boards they would sell a lot more of them.

    However, the Gigabyte 3D1 in x16/x2 mode performs quite well when jumpers are left in normal mode. After the mod to SLI it works fine with drivers to 70.xx.
  • crazyeddie - Tuesday, January 18, 2005 - link

    It would be a little late in the game for Nvidia to go back and do a whole lot of reverse engineering to the NF4 SLI chipset to make it less moddable (new word?). Nvidia will:

    A) Let the NF4 Ultra out the door as is, eat the lost sales of more profitable SLI chipsets, and take solice that their graphic card sales will be quite brisk. This presumes they can actually ship enough video chips to take advantage of the increased demand.

    B) Dry up the current supply of Ultra chipsets and go back to the drawing board to disable them more thoroughly. They will miss out on shipping Ultra chipsets to motherboard manufacturers, which may or may not cause contract problems. It would ensure the continued desirability of the SLI chipset at higher margins, however.

    I've personally been hoping for an inexpensive PCI-E board for the 939 Athlon 64 platform that I can pair with a Radeon X800XL solution. This news story jeapordizes the shipment of the NF4 Ultra if Nvidia is determined to protect margins for the sake of overall volume. I guess it's no loss to me, because I couldn't buy an X800XL right now anyway.

    I guess we'll have to wait and see whether Nvidia wants to focus on volume or margin-per-unit.
  • Wesley Fink - Tuesday, January 18, 2005 - link

    #22 - Your idea was so intriguing I had to give it a try. With the DFI UT Ultra modded to SLI, jumpers in normal (non-SLI) position and the Gigabyte 2 gpu 3D1 I was able to run SLI fine with drivers up to 70.xx. This suggests that the Gigabyte Dual 6600GT might run in the single slot of any nF4 Ultra motherboard in a "semi-SLI" mode. That means 2 video cards are potentially NOT required. Modding to SLI woujld enable a wider range of working drivers. More testing needs to be done before reaching any conclusions.

    I am getting ready to try the Gigabyte 3D1 now in full SLI (x8/x8) mode to see if that works on the DFI.
  • ChiefNutz - Tuesday, January 18, 2005 - link

    #23, #27 I dunno, when you go to the DFI website, it shows a picture with the link in the box contents on the ultra for the box contents, and
    for the main product page. It's sitting right there in 3 of the 4 pictures right below the Package listing? What gives?
  • adnauseam - Tuesday, January 18, 2005 - link

    the one I think everyone is missing is....where do you get a SLI bridge, without purchasing an actual SLI board. Remember the bridges ship with the boards not the cards, because the spacing between the PCIe slots could be different on each maufacturers board. It seems the only way to get one would be to wait until someone who doesnt plan on using it sells one on ebay. unless........there is a way to purchase a replacement....Ill have to check that out actually.............
  • razor2025 - Tuesday, January 18, 2005 - link

    This is awesome find. It gives us more choices. I was planning to buy a NF4 board, so I can use the X800XL I have in pre-order. I didn't want a SLI-ready setup, because the cost is too much. However, if I can get a SLI-capable board (after hack) like the DFI UT for around $130-140, I'll definitely go for them. Most single SLI NF4 boards are fetching around $130-140, and if DFI UT and the Epox board retails for around the same price, everyone who wanted a single SLI NF4 will changed their decision to these awesome boards. Even though I won't be doing SLI anytime soon, I'm sure there will be capable and cheaper cards that can run SLI on these boards down the road. If that doesn't happen, oh well, I still needed a PCI-E board that use Athlon64.

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