How do you enable SLI on two cards that are not the same but are very similar?

by on April 18, 2009

Q: I recently installed two GPU’s in my computer running 64 bit XP and was hoping to run them in SLI configuration. One is a GeForce 8600GT 512MB manufactured by KFA2 and the other is a GeForce 8600GT manufactured by Nvidia. After hooking everything up I found there was no SLI options or multi-GPU settings at all in the Nvidia control panel. My computer has detected both GPU’s so there’s no hardware problem and all the latest drivers have been installed. After digging around for hours in the control panel I found the system information, which told me that my two cards have slightly different clock speeds and various other technical differences. Is this the reason I am not able to enable SLI? Is there any way around this?

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11 Responses to “How do you enable SLI on two cards that are not the same but are very similar?”

    Did you install an SLI bridge connector? One or both of the cards should have come with one.

    Looks kind of like this little piece connecting the top of these two cards here:


    Although I am a n00b I still believe I set up the cards correctly. The SLI bridge is connected properly, as are both the cards, I’m fairly sure.


    here are the specific differences between the two cards:
    On card 1 we have:
    32 stream processors, core clock 600MHz, shader clock 1320 MHz, memory clock 400 MHz, memory interface 128-bit, and video BIOS version

    On card 2 it’s a little different:
    16 stream processors, core clock 540MHz, shader clock 1188MHz, memory clock 300MHz, memory interface 64-bit, and video BIOS version

    Other than that, the cards are the same, and Nvidia control panel recognizes both cards, just no option to SLI. Are these differences too much?


      I’m not sure what that menu is, or how to get to it. I’ve only been looking at the nvidia control panel. Could you tell me where that menu is?

      I’m not being much help here, am I?


    Check your motherboard manual as well, some models require a bios setting be changed to allow SLI mode.


    Are you 100% sure those are both 8600GT cards, and not an 8600GT and an 8500GT? The 8600 should have 32 stream processors, but the 8500 only has 16.

    If you still think these are both 8600GT cards the next step would be for me to take a look at your dxdiag to see your system configuration.

    * On XP: Click Start > Run > Type dxdiag > Click Save all information > Save the text file.
    * On Vista: Click Start(Windows Logo) > In the search bar type dxdiag > Save all information > Save the text file.

    You can e-mail the dxdiag.txt text file to mark(at)


    The vendor sold it as an 8600gt, the box says 8600gt, and the nvidia control panel says 8600gt, but 16 stream processors…


    Yeah, I’m really suspicious about that second card. I think it’s simply too different, and you might have gotten screwed by that vendor. Maybe try ?

    1) 8600GT should have 32 stream processors
    2) nVidia doesn’t sell any video cards directly

    So a few things to try
    Try running GPU-z and see if it shows both cards, do the ‘validation’ step and it will upload your video card specs to the web so I can see them. (just send me the link)

    The directx diag is only showing the one 8600GT card for whatever reason, so maybe GPU-z will have better luck seeing both cards.

    Now, it does look like you’re trying to run a serious setup for gaming. You also might want to consider flipping the two cards you have and swapping in something else. Even a single 8800GT is faster than two 8600GT cards. Here is a great chart from Tom’s hardware that you can mess with to get an idea how different cards and their SLI setups run:,794.html


    Well the vendor had posted the specs of the card before I bought it, so I can’t complain, and supposedly it’s an 8600gt (though maybe a special extra-crappy model or something). As for my setup, I’m not too serious about gaming, and I don’t like to fork out money upgrading graphics cards. I was hoping just for an incremental upgrade, but it looks like the money might go to waste. I don’t think I’ll bother buying an 8800gt, even as cheap as they are now.

    Picked as best answer

    Regarding your link to the GPU-Z data:

    The card has the correct GPU for an 8600GT in it, but still it is a 128meg card, so it’s a very stripped down extra crappy model. So I’m willing to bet that is your problem.

    I’d suggest hitting up someplace with a better reputation (newegg, etc.) in the future to keep from getting burned.