with cooperation between the threads would achieve seamless parallelism. It is important to note that scheduling is not a new concept but it was previously the responsibility of individual driver developers. WDDM attempts to unify the experience across different vendors by controlling the execution of GPU tasks. Cross-process sharing of Direct3D surfaces A Direct3D graphics surface is the memory area that contains information about the textured meshes used for rendering a 2D or 3D scene. WDDM allows Direct3D surfaces to be shared across processes. Thus, an application can incorporate a mesh created by another application into the scene it is rendering. Sharing textures between processes before WDDM was difficult, as it would have required copying the data from video memory to system memory and then back to video memory for the new device. Enhanced fault-tolerance If a WDDM driver hangs or encounters a fault, the graphics stack will restart the driver. A graphics hardware fault will be intercepted and if necessary the driver will be reset. Drivers under Windows XP were free to deal with hardware faults as they saw fit either by reporting it to the user or by attempting to recover silently. In some cases when the display driver can be safely stopped, Windows XP may instead alert about the display driver crash, while also disabling the video driver, thus switching down the screen resolution to 640x480 with only 16 colors. With a WDDM driver, the screen resolution will most likely be unaffected; all hardware faults cause the driver to be reset and the user will be notified by a popup; this unifies the behavior across vendors. Previous drivers were fully implemented in kernel mode, whereas WDDM is implemented partly in user mode. If the user mode area fails with an unrecoverable error, it will, at the most, cause the application to quit unexpectedly instead of producing a blue screen error as it would in previous driver models. WDDM also allows the graphics hardware to be reset and users to update drivers without requiring a reboot. Limitations The new driver model requires the graphics hardware to have Shader Model 2.0 support at least, since the fixed function pipeline is now translated to 2.0 shaders. However, according to Microsoft as of 2009, only about 1–2 percent of the hardware running Windows Vista used the XDDM, with the rest already WDDM capable. It also requires some other hardware features; consequently