A communication system is presented which consists of a switch (Datakit [Fraser 1979]) with associated control and interface hardware and software. The switch offers virtual circuit service which is internally implemented through packet switching. The users of the communication system are operating systems; using our communication system, we have implemented a network of UNIXTM systems and a new distributed operating system derived from UNIX. Our work concentrated on the performance of the subscriber-switch interface; on the reliability and recoverability of the switching service; and on the exploitation of the circuit concept for operating system design.

The popular UNIXTM operating system provides time-sharing service on a single computer. This paper reports on the design and implementation of a distributed UNIX system. The new operating system consists of two components: the S-UNIX subsystem provides a complete UNIX process environment enhanced by access to remote files; the F-UNIX subsystem is specialized to offer remote file service. A system can be configured out of many computers which operate either under the S-UNIX or the F-UNIX operating subsystem. The file servers together present the view of a single global file system. A single-service view is presented to any user terminal connected to one of the S-UNIX subsystems.