As many older applications are not aware of the Desktop Window Manager reverse compatibility is required. This is accomplished by redirecting the graphics output through GDI or DirectX buffers to render the desktop.
When using GDI each application is required to render itself when receiving a notice from the GDI buffer that it is in view. The rendering then rasterizes the user interface in the buffer located in video memory. AGDI writes to a buffer for each window that is equal to the size of the window and then a compositor that is part of the Windows Desktop Manager writes to a buffer the size of the desktop creating a DirectX surface. This work around is required as GDI is unable to the pixel format used by DirectX.
When using a DirectX application windows write directly to the three dimensional surface which is shared with the Windows Display Driver Model. A compositor then renders the shared three dimensional surface into the final desktop. By sharing the desktop with the Windows Display Driver Model applications with both GDI – which is more widely used and DirectX can share the same desktop environment and be integrated into a smooth surface. However if an application used both DirectX and GDI to render itself the Desktop Window Manager cannot support it and is temporarily disabled for that application while it is running.