[vbox-dev] Monitor count limitations

Vitali Pelenjow Vitali.Pelenjow at oracle.com
Tue Sep 2 12:57:22 GMT 2014


> 2014-09-01 22:23 GMT+03:00 Rūdolfs Bundulis 
> <rudolfs.bundulis at gmail.com <mailto:rudolfs.bundulis at gmail.com>>:
>     Hi,
>     any hints on how to understand if a Windows 7 guest OS uses XPDM
>     or WDDM driver? I would be interrested to see if with XPDM I can
>     actually reduce the needed memory for the surfaces.

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.


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