The DOMAIN system is an architecture for networks of personal workstations and servers which creates an integrated distributed computing environment. Its distinctive features include: a network-wide file system of objects addressed by unique identifiers (UID's); the abstraction of a single level store for transparently accessing all objects, regardless of their location in the network; and a network-wide hierarchical name space. The implementations of these facilities exhibit several interesting approaches to layering the system software. In addition to network transparent data access, interprocess communication is provided as a basis for constructing distributed applications; as a result, we have some experience to guide the choice between these two alternative implementation techniques. Networks utilizing this architecture have been Operational for almost three years; some experience with it and lessons derived from that experience are presented, as are some performance data.

The use of UIDs as internal names in an operating system for a local network is discussed. The use of internal names in other distributed systems is briefly surveyed. For this system, UIDs were chosen because of their intrinsic location independence and because they seemed to lend themselves to a clean structure for the operating system nucleus. The problems created by UIDs were: generating UIDs; locating objects; supporting multiple versions of objects; replicating objects; and losing objects. Some solutions to these problems are presented; for others, no satisfactory solution has yet been implemented.