8½, the Plan 9 Window System

Rob Pike
rob@plan9.bell-labs.com

ABSTRACT

The Plan 9 window system, 8½, is a modest-sized program of novel design. It provides textual I/O and bitmap graphic services to both local and remote client programs by offering a multiplexed file service to those clients. It serves traditional UNIX files like /dev/tty as well as more unusual ones that provide access to the mouse and the raw screen. Bitmap graphics operations are provided by serving a file called /dev/bitblt that interprets client messages to perform raster operations. The file service that 8½ offers its clients is identical to that it uses for its own implementation, so it is fundamentally no more than a multiplexer. This architecture has some rewarding symmetries and can be implemented compactly.