Direct Rendering Infrastructure (DRI)
One of the problems with Direct Rendering is that other applications (say the X11 server, or other OpenGL clients) might want to talk to the hardware at the same time. In addition there can be problems with security, multiple users, and several other things caused by the complexity of Unix. An intricate software design called the Direct Rendering Infrastructure coordinates everything and prevents problems. The DRI used on Linux was designed and implemented by Precision Insight (who were recently bought by VA Software, former VA Linux). The DRI was integrated into XFree86 4.0 and is available in that and all subsequent releases; current development is concentrating on Xorg instead of XFree86.