Failed test for detecting video memory size

I have a .net/DirectX-based rendering library. At program start, we try to find out the amount of physical video RAM. Detecting the amount of physical video memory is important, to know how much can be used for textures (If you've done serious directX you probably already know).

Video RAM is detected by executing the following WMI code:

var searcher = new ManagementObjectSearcher("Select * from Win32_VideoController");

foreach(ManagementObject videoCard in searcher.Get())
{
    _numVideoCards++;
    foreach (PropertyData propertyData in videoCard.Properties)
    {
        if (propertyData.Name == "AdapterRAM" && propertyData.Value != null)
        {
            _adapterRAM = Math.Max( (UInt32)(propertyData.Value), _adapterRAM );
        }
    }
}

This code was written years ago by people who knew directX better than me.

The issue is that this call is now failing unpredictably on customer hardware (_adapterRAM == 0 after the code completes, and an exception is logged).

I would like to change the test, but I hesitate because I expect there is a reason why the video memory is detected this way, and directly through DirectX.

My question is twofold:

• Does anyone know why you'd do this with WMI, and/or
• do you know a more reiliable way to detect the amount of physical video RAM?

P.S.: We're not interested in shared memory video cards (e.g. Intel). We use SlimDX if that makes a difference.

Simply because D3D9 doesn't expose the amount of physical memory on the device. WMI is the only vendor independent option as far as I know.

With D3D10 and D3D11 (making use of DXGI) you retrieve it using field DedicatedVideoMemory of struct DXGI_ADAPTER_DESC and voilà. So if you are targeting Vista or Seven OS, this should work.

An option (but not nice) would be to use OpenGL and proprietary extensions like GL_ATI_meminfo or using proprietary IHV api like NVAPI and making a thin wrapper around them with C++/CLI.