moved to marvin:hardware

I have been using Radeon + two Geforces in one computer, but only for BOINC, never tried to play on them. It was working without problems.

In theory it works, at least, on XP and Windows 7 or newer.
Windows Vista had an update to the display driver model, but they did not introduce a new way to make multiple drivers cooperate yet, so you can only use videocards that can run on the same driver (doesn't have to be the same card). In Windows 7 this was implemented.
I've done this a lot with my own software, which can render on multiple GPUs at the same time. Eg I can use an onboard GPU for light rendering (preview windows, simple GUI stuff), and one or more discrete cards for the heavy 3d lifting.

In practice, the problem is that you need to specify to D3D or OpenGL that you want to use a specific videocard. Most games have not implemented any options/menus for this, so they will just pick the 'default' card. And I don't think there is a way to select which card should be the 'default' (I think it's just whichever card was first installed). So you can't easily select which card to run a game on, as far as I know. But perhaps there are tools/wrappers out there to help with that. I never tried.

I think, the "default card" is the one you are using for desktop (or Windows is using while it's loading).
Switching between AGP and PCI/PCI-e, should be possible from BIOS.
Older games have GPU select in first start configuration menu (Stunt GP or Dethkarz for example), but I don't know how it works when two GPU's are detected (menu usually is for Software vs. Hardware rendering).
Also, I doubt switching between different default GPUs is possible without at least a restart.

kva wrote:

I have been using Radeon + two Geforces in one computer, but only for BOINC, never tried to play on them. It was working without problems.

Which driver should you install first? Radeon, or GeForce? Or does it matter?

agent_x007 wrote:

I think, the "default card" is the one you are using for desktop (or Windows is using while it's loading).
Switching between AGP and PCI/PCI-e, should be possible from BIOS.

Well in my case, both cards would be PCI-e. I don't mind restarting the computer though, as long as the game gets the correct video card to run on.

Two pci-e GPUs should be no problem, even AGP + PCI works at the same time (if you have board that support it). Doesn't matter which driver you install first, both should work simultaneously at the end. If your game can switch what GPU to use, then no restart is needed, simply select the one you want to use and it should run on the GPU preffered. Of course you need either two monitors or one with two inputs.
When the game can run only on default GPU, then restart and switching primary pci-e slot in bios might be needed. Maybe (I'm not sure) the primary GPU could be considered the one the one rendering primary desktop in windows (the one with taskbar). In that case perhaps it is possible to switch it without restart simply by selecting the other's GPU desktop as primary.

havli wrote:

Two pci-e GPUs should be no problem, even AGP + PCI works at the same time (if you have board that support it). Doesn't matter which driver you install first, both should work simultaneously at the end. If your game can switch what GPU to use, then no restart is needed, simply select the one you want to use and it should run on the GPU preffered. Of course you need either two monitors or one with two inputs.
When the game can run only on default GPU, then restart and switching primary pci-e slot in bios might be needed. Maybe (I'm not sure) the primary GPU could be considered the one the one rendering primary desktop in windows (the one with taskbar). In that case perhaps it is possible to switch it without restart simply by selecting the other's GPU desktop as primary.

Indeed.

However, I read Radeon driver and GeForce driver are such pain when installed in the same system. Is that true? Which driver should I install first? And such I switch to plain VGA before installing the next vendor's driver?

There is no pain, both drivers coexist perfectly fine. Well, maybe AMD drivers can show some minor issues from time to time - one example from my experience. I was using R9 290 until recently and then upgraded to GTX 1070... so I've installed nvidia drivers and left old AMD drivers in place. No problems except once per month there is popup message that informs me that new AMD drivers are available and asks me if I want to upgrade. 🤣 Obviously that utility isn't aware AMD GPU is no longer present in this PC.

Just install first the driver for your primary VGA and the other driver second. There is no need to swith to VGA mode or anything.

havli wrote:

There is no pain, both drivers coexist perfectly fine. Well, maybe AMD drivers can show some minor issues from time to time - one example from my experience. I was using R9 290 until recently and then upgraded to GTX 1070... so I've installed nvidia drivers and left old AMD drivers in place. No problems except once per month there is popup message that informs me that new AMD drivers are available and asks me if I want to upgrade. 🤣 Obviously that utility isn't aware AMD GPU is no longer present in this PC.

Just install first the driver for your primary VGA and the other driver second. There is no need to swith to VGA mode or anything.

Ah, I see. Thanks!

Time to hunt for GeForce GTX 295 and Radeon HD 6990, I guess.