To virtualize video memory, the video memory manager in Windows Vista assigns a virtual address range to every video memory resource. This range is conceptually similar to the copy that an application might create. However, the video memory manager manages the process more efficiently than the application might. The video memory manager uses the virtual address range to handle transitions or over-commitment of video memory. However, the virtual address range is typically unused on a system that has lots of video memory. As long as this virtual address range remains unused, no physical memory is allocated for it. In contrast, the system memory copy that is maintained in the older driver model is guaranteed to be fully populated with physical memory.
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