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NoelC
01-11-2011, 06:55 AM
I've doing research on the modern WDDM and how modern graphics cards with huge amounts of GPU RAM map to 32 bit Windows (e.g., Windows 7) systems.

I find a lot of documentation about how the entire GPU memory space must be mapped to the CPU address space, but this information appears outdated, and contradicts observations on modern systems.

I've found some fairly general wording in the Windows WDDM documentation that says stuff like:

http://download.microsoft.com/download/9/c/5/9c5b2167-8017-4bae-9fde-d599bac8184a/graphicsmemory.doc

Discrete graphics adapters generally share a portion of system memory with the CPU. Typically, these adapters do not ask for dedicated use of system memory for graphics, thus leaving more resources available for the rest of the system.

It seems clear the modern WDDM has "changed the rules" and made things more complicated, so statements like "installing a 1 GB video card will reduce your available CPU RAM by 1 GB" are now just wrong - they're just too simplistic.

But I'd like to see it written down, from an authoritative source.

Can you point me to documentation on this? Something that specifically describes the strategy for mapping address range windows to GPU memory in modern 32 bit operating systems?

Thanks!

-Noel

Stephen A
01-11-2011, 11:22 AM
Right from the horse's mouth: http://msdn.microsoft.com/en-us/library/aa366778(v=vs.85).aspx

NoelC
01-11-2011, 03:12 PM
Thanks, but that page does not address the key point of my request.

Basically it says that devices map their address spaces to the the space below 4GB on a 32 bit system. That's pretty common knowledge.

But how much?

Some sources say that the modern video card typically opens a window of up to 512 MB, others swear that the entire video card memory must be mapped in its entirety to the CPU's address space.

Given that a modern graphics cards are offering 1, 2, 4, or ?? GB of dedicated RAM, I'm surprised there is not more solid info out there on how this impacts the CPU's address space. Maybe 32 bit Windows is just finally on its way out and no one really cares any more.

What OS do gamers use primarily today?

-Noel

Stephen A
01-12-2011, 03:04 PM
What OS do gamers use primarily today?

Windows 7 x64, according to http://store.steampowered.com/hwsurvey

There are a few successful games that no longer support Windows XP, e.g. Just Cause 2. We'll slowly see more and more of those, as WinXP is gradually phased out.