The Desktop Window Manager started when Vista was being produced just under a codename Long Horn at Microsoft. Codenamed Aero during development the Desktop Window Manager is a change to the stacking window manager used in previous Microsoft Windows operating systems.
The Desktop Window Manager as of Windows 7 sends data directly to the video card instead of keeping and processing the Data in the computers Random Access Memory (RAM). This allows for better resource management as well as better visual effects that are a composite of different applications. For example you can make windows partially transparent with the Windows Desktop manager.
With the implementation of the Desktop Window Manager the desktop has become a full sized Direct3D surface. Each window consists of two triangles that are inverted and placed next to each other to create a two dimensional rectangle to represent the window. Transformations of windows using the Desktop Window Manager are accomplished through the use of shader programs that are built into the operating system.
By using the Media Integration Layers the Desktop Window Manager creates different windows as composition nodes made up of a composition tree. The complete desktop makes up a composition tree which the Media Integration Layer renders from the window that is below all the other windows to the window at the surface of your desktop. By rendering in this manner the Windows Desktop Manager allows for every window to affect the color and shade of a pixel when using transparency by running the open windows through the built in Pixel Shader version 2.0. The shader calculates the appropriate pixel colors allowing the Media Integration Layer to achieve the blur effect so common in today’s Windows operating systems.
As the Media Integration Layer handles all the repainting, processing and refreshing of the screen the applications are no longer responsible freeing up valuable computer resources. By using double-buffering and culling the Windows Desktop Manager is able to provide a smooth, resource friendly three dimensional environment on your desktop.