some SM 2.0-supporting hardware such as the Intel GMA 900 fails the WDDM certification. One of the limitations of WDDM driver model version 1.0 is that it does not support multiple drivers in a multi-adapter, multi-monitor setup. If a multi-monitor system has more than one graphics adapter powering the monitors, both the adaptors must use the same WDDM driver. If more than one driver is used, Windows will disable one of them. WDDM 1.1 does not have this limitation. WDDM 1.0/1.1 does not allow some modes that were previously handled by the driver such as spanning mode (stretching the desktop across two monitors) although Dual View is still available. Need for a new display driver model One of the chief scenarios the Windows Display Driver Model enables is the Desktop Window Manager. Since the desktop and application windows managed by DWM are Direct3D applications, the number of open windows directly affects the amount of video memory required. Because there is no limit on the number of open windows, the video memory available may prove insufficient, necessitating virtualization. As the window contents that DWM composes into the final desktop are generated by different processes, cross-process surface sharing is necessary. Also, because there can be other DirectX applications running alongside DWM on the DWM-managed desktop, they must be able to access the GPU in a shared manner, necessitating scheduling. Though this is true for Microsoft's implementation of a composited desktop under Windows Vista, on the other hand, a composited desktop need not theoretically require a new display driver model to work as expected. Successful implementations of composited desktops were done before Windows Vista on other platforms such as Quartz, Compiz, WindowFX. The approach Microsoft attempted was to try to make sure WDDM was a unified experience across different GPUs from multiple vendors by standardizing their features and performance. The software features missing from other driver models could be made immaterial by extensions or if a less restrictive or simply different driver model was in place. History WDDM 1.0 Windows Vista introduced WDDM 1.0 as a new display driver architecture designed to be better performing, more reliable, and support new technologies including HDCP. Hybrid Sleep, which combines hibernation and sleep mode functionality for enhanced stability in the event of power failure, also requires WDDM. WDDM 1.1 Windows 7 supports major additions to WDDM known as WDDM 1.1; the details of this new version