Plan 9 is divided according to service functions. CPU servers concentrate computing power into large multiprocessors; file servers provide repositories for storage and terminals give each user of the system a dedicated computer with bitmap screen and mouse on which to run a window system. The sharing of computing and file storage services provides a sense of community for a group of programmers, amortises costs and centralises and hence simplifies management and administration.
The pieces communicate by a single protocol, built above a reliable data transport layer offered by an appropriate network, that defines each service as a rooted tree of files. Even for services not usually considered as files, the unified design permits some simplification. Each process has a local file name space that contains attachments to all services the process is using and thereby to the files in those services. One of the most important jobs of a terminal is to support its user's customised view of the entire system as represented by the services visible in the name space.