This is because Windows 7 supports (limited) hardware acceleration for GDI and in doing so does not need to keep a copy of the buffer in system RAM so that the CPU can write to it.īecause the compositor has access to the graphics of all applications, it easily allows visual effects that string together visuals from multiple applications, such as transparency.
Under Windows 7 and with WDDM 1.1 drivers, DWM only writes the program's buffer to the video RAM, even if it is a graphics device interface (GDI) program. By comparison, the stacking window manager in Windows XP and earlier (and also Windows Vista and Windows 7 with Windows Aero disabled) comprises a single display buffer to which all programs write.ĭWM works in different ways depending on the operating system (Windows 7 or Windows Vista) and on the version of the graphics drivers it uses ( WDDM 1.0 or 1.1). This means that each program has a buffer that it writes data to DWM then composites each program's buffer into a final image. The Desktop Window Manager is a compositing window manager.
