"The design of DRI2, or the Direct Rendering
Infrastructure 2, was a modest improvement over DRI (DRI2 design
page) and noticeably to end-users it allows (accelerated) direct
rendering to redirected windows. This becomes noticeable (or there
the lack of) when using a compositing manager (Compiz) and watching
a video or running an OpenGL application. DRI2 though has been
dropped from the X Server 1.5 series due to its dependence on the
TTM memory manager. "