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I have seen lots of different posts on this issue, but I cannot figure out what to do. I hope we can collect the available information in one place, so that they can be useful for others.

Is it possible to have multiple (3+) monitors running on two different graphics cards?

I have

  • 1x nVidia GeForce GTX 550 with 2 DVI ports and
  • 1x Intel integrated graphics, with 2 DVI ports.

I understand that they would be running on different instances of X servers. Is that correct? Could someone point me in the right direction to start?

On Windows it's so simple, there is no additional thing to do other than going in display preferences and activating all 3+ monitors. They can even be laid out alternating one monitor from one graphics card with another monitor from the other card.

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2 Answers 2

In my experience this just does not effing work in Ubuntu currently. I will say that if you have to edit xorg.conf in a reasonably current version of Ubuntu (anything post-Unity), you're doing it wrong -- XRANDR does much better on its own. It's a shame, because the Intel graphics these days are so good, I don't want the adapter to go to waste, but X doesn't know how to use two different GPUs simultaneously.

This may have something to do with the fact that the Intel adapter doesn't actually show up as "VGA compatible" in lspci when you've got a discrete card connected -- but that's all the sleuthing I managed. You should file a bug report; I keep meaning to get around to it.

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Thanks for your help. I'll try to file the bug and post the link here when it's done. –  gozzilli Oct 8 '12 at 14:05
    
Sounds good! I believe that when Windows does this, the primary (discrete) card just winds up rendering to a framebuffer the size of all 3+ screens in 2D mode (something that modern discrete cards can handle no problem). Monitors are only tied to the GPU they're actually connected to in 3D modes -- though there are also proprietary tools like Virtu to offload lesser hardware-accelerated tasks like video decoding to the integrated GPU. Not sure how incompatible this is with the way X does things, but I do think that lspci issue is a good place to start. –  serilain Oct 16 '12 at 16:29
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Since 13.04 or kernel 3.8 the intel-driver can handle this! (before, the 3. monitor only shows crap, but was activatable) So using the open-source-nvidia-drivers together with the newest kernel should work. It does for me with the actual daily build of 13.04.

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Does it only work with the open source nvidia drivers? –  gozzilli Mar 25 '13 at 14:49
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