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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  • CrystalBay - Wednesday, November 24, 2004 - link

    #61 good point, I also wonder how well it runs at super high resolutions... Reply
  • PrinceGaz - Wednesday, November 24, 2004 - link

    We've seen profiles for many games in nVidia drivers since the 5x.xx series, I expect the SLI mode is just something they've added to it for when the card is running in an SLI mode. If in doubt, I'd have thought SLI AFR will be fine for most games that don't have a profile defined (assuming you can choose SLI mode), or SFR for those games that use motion-blurring (usually certain types of racing games). Reply
  • Pampero - Wednesday, November 24, 2004 - link

    where in the review talk about the profiles?
    Is there a list of the games that can enable SLI?

    Reply
  • Gatak - Wednesday, November 24, 2004 - link

    Where is the 2048x1536 tests? It is clear that 1600x1200 is no match for the SLI setup in most games. Why not do testing at higher resolution.

    If 2048x1536 ran smoothly, Then the demand for better monitors would be stronger - giving manufacturers reason to make better monitors for us =).
    Reply
  • PrinceGaz - Wednesday, November 24, 2004 - link

    #55- If SLI is only able to be used on games nVidia have profiled like you say, and that the user cannot themselves force it to run in SLI AFR or SFR mode, then that's a serious problem for people who play non-mainstream games who might be considering SLI.

    After reading this article, I now believe more than ever that the only people who should be seriously considering SLI are those who are willing to buy two 6800GT or 6800 Ultra cards in one go, in order to have a top of the range system. The upgrade option doesn't make sense.

    Anand didn't compare the costs of an SLI upgrade against a non-SLI upgrade; instead he compared buying a second 6600GT later on when they're cheaper, to buying a high-end card initially and *not* doing any upgrade. Of course it's going to be more expensive if you buy a high-end card from the outset.

    The true upgrade alternative is that instead of buying a second (now cheaper) 6600GT to achieve roughly 6800GT performance, you would sell your 6600GT while it can still fetch a good price and put the money towards a (now also cheaper) 6800GT or maybe a mid-range next-generation card that has the required performance. When you look at how much prices fall on high-end cards when something even a little faster comes out, pushing them nearer to mid-range cards; it should be obvious that replacing the card with a faster one is a more cost-effective option for anyone considering an upgrade at a later date, than buying a second identical card on top of the one you already have.

    Yes there's the hassle of selling your first card, but not only do you have total flexibility over what you upgrade to (with SLI you have none); you also don't need an SLI mobo, you won't have two graphics-cards generating excess noise, and you'll have a lot more PCI/PCI-e slots left free for other cards.
    Reply
  • bob661 - Wednesday, November 24, 2004 - link

    IMHO, SLI is for people like me and also for people that need to have the latest and greatest. People like me don't upgrade every 3 months, 6 months, or even a year. I upgrade every 2.5 to 3 years. It would be nice to be able to run 2006 or 2007 games on 2004 technology. Who knows, this might extend my upgrades to 4 years. ;-) Reply
  • Momental - Wednesday, November 24, 2004 - link

    #56 I would imagine that nVidia is aware of this and who knows, they may implement a utility within their driver that automatically flashes the BIOS of the "older" card, if one is detected. Either that, or they could write something into the driver to search for another GPU and once it's found, ask you if you would like to flash its BIOS upon restart. And voila!

    The fact of the matter is that it's way too early to speculate as to whether or not SLI is a viable and cost-effective solution. Something tells me that it will be because it's not like the "next big thing" ie: cards that are twice as fast, are right around the corner. If they were, then I'd say 'no'. It isn't worth it for reasons stated by #42.
    Reply
  • nserra - Wednesday, November 24, 2004 - link

    I think the issue of the card to MUST have the same bios is ENORMOUS. So the buy one now and buy the other LATER will "not" be possible. I doubt that a year old card has the same BIOS of brand new one.

    Too much “issues”…
    Reply
  • nserra - Wednesday, November 24, 2004 - link

    I think the issue of the card to MUST have the same bios is ENORMOUS. So the buy one now and buy the other lather will "not" be possible. I doubt that a year old card has the same BIOS of brand new one.

    Too much “issues”…
    Reply
  • Elliot - Wednesday, November 24, 2004 - link

    I want one of this SLI boards but the article said that you can force the driver to enable SLI on games without profiles on Nvidia drivers but this is not real.

    If no SLI profile exists for a game, there is no SLI rendering. It is not possible to force SLI mode or generate your own profile. According to NVIDIA however the driver already contains over 50 profiles for games running with SLI. For newer titles this therefore means that SLI system owners have to wait for a new driver. But even then there is no guarantee that SLI will be possible with a particular game. So this is not very good news.
    Reply

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