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My PC (Compaq Presario) has an onboard Intel 3100 which is pretty lame wbut would be useful for testing on, or a 3rd monitor. I've then got a nVidia PCIx card installed. I can't seem to find a way to turn both on at once... is it likely this is a BIOS limitation?

Running Windows 7.

The official page suggests I can't do this but I wondered if there is a way?

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On some systems it will work OK. – user84069 Jun 1 '11 at 23:00
indeed, i have seen this done, but it didnt work for me on a similar system with a slightly differing motherboard. – Sirex Jul 11 '11 at 14:26
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To flesh out Sathya's answer a bit: In most systems, the same PCIe lanes are used for both the IGP and the PCIe-x16 slot for the video card. So either the slot can be used or the IGP. This means you can't even put non-video card devices (e.g. RAID controllers) into the x16 slot without losing access to the IGP -- you'd still have to install a video card in a different slot!

Late Edit: It appears that on Sandy Bridge systems with an H67 (and probably Z68, when they launch) chipsets, it's possible to run both the onboard GPU and an add-on graphics card at the same time. Other 6-series (and later) chipsets may work as long as both the CPU & MB Chipset support Intel's Flexible Display Interface, a DisplayPort-based standard that gives the integrated GPU a direct connection to the onboard video connectors.

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Annoying but thanks for explaining why the limitation exists, at least I can reboot and toggle through BIOS fairly easily. – John Feb 3 '11 at 14:34
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You say that "It appears" this is possible on Sandy Bridge systems. Do you have any documentation or reference that confirms this? Have you done it personally? I notice that this question was closed as a duplicate of this one, but it's clearly not... Your latest edit makes it appear that the answer is quite different in the case of Sandy Bridge. – Cody Gray Jul 11 '11 at 10:49
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@Cody: I think the key is that the CPU & Chipset must support Intel's Flexible Display Interface in order to work alongside a discrete GPU. That's what gives the system a direct connection from the integrated GPU to the onboard video connectors instead of sharing PCIe lanes. I don't have direct experience myself though, so I can't give you a definitive answer. – afrazier Jul 11 '11 at 13:11
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up vote 2 down vote

Unfortunately, there's no way around this limitation - using an external card automatically turns off the IGP.

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Just for clarity, this is true for many, but not all motherboards. I have personally run both an AGP card and the onboard to support two monitors on an older system. I have also heard of systems which will permit running the onbaord alongside a PCIe based card, but I have not tested that or researched it extensively. – TimothyAWiseman Jan 19 at 16:50
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@TimothyAWiseman: AGP was a dedicated interface, and at the time northbridge integrated video was probably done via a PCI interface (especially with Intel chipsets). That would have greatly limited the possibility of resource contention. That's just a hunch though. Ultimately the answer varied from chipset to chipset. – afrazier Mar 26 at 12:34
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