SLI – The Requirements

There’s been a lot of confusion as to what is required to run a SLI configuration, so we put together a quick list of the things you’ll need:

  • Everything necessary to put together a working system, including SLI motherboard
  • Two graphics cards with identical GPUs from the same manufacturer.  Video BIOS revisions must also be identical. Note that if the cards run at different clock speeds, the driver will run both cards at the lower clock speed of the two.  NVIDIA has announced their SLI certification program, which means that two SLI certified cards should have no problems working in tandem. Currently only NVIDIA cards will work in SLI mode although ATI plans on introducing SLI technology in 2005.
  • A power supply capable of supplying adequate power to the system as well as both graphics cards.  Note: you may need one or two 2 x 4-pin to 1 x 6-pin PCI Express power adapters if you are using two 6800GT or 6800 Ultra graphics card with a power supply that either has no or only one 6-pin PCI Express power connector.
  • A SLI video bridge connector.  This connector should be provided with your nForce4 SLI motherboard. 
  • NVIDIA drivers with SLI support.  Currently the 66.93s are the only NVIDIA sanctioned drivers with SLI support, however NVIDIA is working on rolling in SLI support to all of their drivers, including the newly released 67.02 driver. 

It’s no big surprise that you can’t use different, GPUs; in our tests we tried combining a 6800 Ultra with a 6600GT, but NVIDIA’s driver wouldn’t even let us enable SLI on the combination.  When we tried to combine two different 6600GTs (non SLI certified) we could enable SLI through the driver, but there were tons of stability problems.  Accessing the NVIDIA Control Panel would cause the system to lock up, presumably because the control panel had issues reading from two different video BIOSes.  If we didn’t bother with the NVIDIA Control Panel and just tried to run a game we were met with video corruption issues and lockups.  Right now it seems like the only option for SLI is to have two identical cards; in theory they can be from different manufacturers as long as the video BIOSes and all of the hardware specifications are identical.  In order to make upgrading easier, NVIDIA introduced their SLI certification program which is designed to ensure compatibility between all identical-GPU cards going forward.  Only time will tell whether or not this actually pans out to make upgrading to a SLI configuration easy.

One thing to make sure you have are sufficient power connectors coming off of your power supply.  If you are using two 6600GTs then it’s not a big deal, since the cards themselves don’t require any external power.  However, with two 6800GTs, each card is outfitted with a 6-pin PCI Express power connector, which must be used for proper/stable SLI operation.  Since most power supplies only include one (or no) PCI Express power connectors, chances are that you’ll have to use a 4-pin molex to 6-pin PCI Express power adapter, which takes two regular 4-pin power connectors and combines them into a single 6-pin PCI Express connector.  You should, in theory, use two separate power cables with the adapter (in order to avoid pulling too much current off of a single cable and violating the ATX spec) but in practice we had no issues with using two connectors off of a single cable to power one of the graphics cards.  If you have no PCI Express power connectors on your power supply then you’d need four separate power connectors just to power your graphics cards, add another one for ASUS EZ-PLUG and then you can start thinking about powering up things like your hard drive and DVD drive.  While purchasing a SLI motherboard will pave a nice upgrade path for you in the future, you may need to enable that future by upgrading your power supply as well.

ASUS’ A8N-SLI Deluxe Enabling SLI
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  • glennpratt - Wednesday, November 24, 2004 - link

    51 - Yeah, and the Voodoo 2 used analog to pass the signal from one card to the other externally. What would you suggest, nVidia make a card that is PCI and combines the signal using analog cables degrading your video quality? Idiocy.

    How many people owned V2 SLI setup and ran it on a crappy computer anyway?
    Reply
  • bob661 - Wednesday, November 24, 2004 - link

    You guys could buy a cheaper CPU and do a mild overclock to get the performance needed. I have a 3500 and I still plan on getting SLI. There's ways to get around the price issue. If I was buying a new system right now I would've gotten a 3200 "winnie" and OC'd it to 2.6GHz. That would put you at FX-55 speeds. If you're lucky you could hit 2.8 to 2.9GHz. Reply
  • bob661 - Wednesday, November 24, 2004 - link

    #49
    You don't need an extravagent budget to afford a monitor that can handle 1600x1200. The Samsung SyncMaster 997DF-T/T 19" CRT can do that for $209 on Newegg.com. I have the older 955DF version which does it too.
    Reply
  • nserra - Wednesday, November 24, 2004 - link

    VOODOO2 didnt NEED any of this, it worked on any MOBO, any monitor, any CARD, any ...... Reply
  • nserra - Wednesday, November 24, 2004 - link

    Buy Monitor.
    Buy PSU.
    Buy MOBO.
    Buy 2 graphics cards.
    Buy good CASE.
    Buy the top of the line processor.


    Too much buys, And all of these itens ALL HAVE TO BE TOP ($$$) OF THE LINE!!!

    I dont have the money, sorry not for me.
    Reply
  • Gundamit - Wednesday, November 24, 2004 - link

    It sounds like if you don't already have a monitor that supports at 1600x1200 you'll have a hard time justifying the SLI expense since you won't see nearly as much performance gain over the single card set-ups at lower resolutions. Just one more expense to consider. Thank goodness LCD panel prices seem to be dropping. I'm onboard for SLI with 6800GTs late Q1 '05. Should be plenty of info and mobo selections out by then. Reply
  • AtaStrumf - Wednesday, November 24, 2004 - link

    I said it before and it looks like I need to say it again:

    SLI like performance improvement (40 - 70% where it counts) in a single GPU over the previous generation single GPU isn't going to happen for AT LEAST 2 years! Example 9700 Pro (2002)/X800XT (2004)

    The other benefit is obviously MUCH lower upgrade cost. Theoretical example: an new $200 9800 Pro or $400 GF 6800 GT and this is really the worst case scenario for SLI -- it would have a lot of performance to make up; but I think that won't happen for a long time.

    And don't forget that we are hitting walls with current technologies, so future generation cards may take much longer than 2 years to bring the 9700/X800 like performance improvement.

    Just look at what ATi is doing. They're going for SLI as well, because there is no way in hell they can compete with it with a single GPU or any kind of single card design that woudn't require it's own power supply and air conditioning unit.

    SLI and dual core is the future; just not for me :-( TOO EXPENSIVE!
    Reply
  • SignalPST - Wednesday, November 24, 2004 - link

    Thank you for the article, Anand. It was very informative and exciting.

    I would like to make a suggestion. Since SLI configurations, as everyone knows, is targeted towards the very top notch enthusiasts, I think it would make a lot of sense to include benchmarks using HDTV(1920x1080) resolutions and the 2048x1536 resolution. A lot of high end 22" CRT monitors as well as high end 23" widescreen LCD's support these resolutions. I imagine these enthusiasts looking for SLI solutions would also be using those types of displays and wondering what kind of performance they would get with their dual video card setup.

    -SignalPST
    Reply
  • SuperStrokey - Wednesday, November 24, 2004 - link

    I wish this would work with 2 agp cards too, would be nice if i could upgrade my bfg6800 gt to a secong one on teh cheap when the new cards come out rather than having to buy a new card. Reply
  • kongming - Wednesday, November 24, 2004 - link

    Nevermind, the V9999 is still just AGP for the time being. Hopefully, they will offer this card in PCI-e in the future. Reply

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