[vbox-dev] Monitor count limitations

Klaus Espenlaub klaus.espenlaub at oracle.com
Tue Sep 2 13:18:52 GMT 2014

BTW, the GUI uses the OS type to make its guesses and recommendations. 
you can exploit that, because the OS type is not used for much besides 
picking suitable defaults - so create the VM with the correct OS type, 
and later re-declare it to be Linux. That way the GUI doesn't try to be 
"helpful", and you should be able to reach the limits...

On 02.09.2014 15:12, Rūdolfs Bundulis wrote:
>     Look at the guest Computer/Properties/Device Manager/Display
>     Adapters/VirtualBox Graphics Adapter/Driver/Driver Details
>     XPDM files are VBoxVideo.sys and VBoxDisp.dll
>     XPDM requires less guest VRAM, it mostly needs VRAM for the screen
>     surface. With 256MB of VRAM it is able to support 24 or 25 monitors at
>     1920x1200x32 each.
>     One screen needs ~9MB, which gives a hard limit 256/9 ~= 28 screens. But
>     since some VRAM is needed for other purposes, it is better not to use
>     the maximum.
>     The performance will be probably a bit worse compared to the case when
>     each guest screen has enough VRAM for a full resolution offscreen
>     surface.
>     I just tested a VBoxHeadless VM with 24 monitors at 1920x1200 and 256 MB
>     of guest VRAM and it seems to work fine.
> Thanks a lot, I'll try that out, I guess, since I checked the Direct3D
> support in the guest additions I could be using WDDM, I'll verify it and
> if so make a clean install and try XPDM. Since my current test wall is
> 5x5 25 would be great.  I simply got confused when I found the code i
> pasted here in a post above in the Qt GUI that does a hard
> multiplication with 3 to calculate the needed video memory.
> Rudolfs

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