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The DEMOS/MP operating system has moved from a supercomputer with a simple addressing structure to a network of microcomputers. This transformation was done without significant changes to the semantics of the original DEMOS, i.e. existing DEMOS programs should run on DEMOS/MP. The changes to DEMOS were simplified by the structure of its primitive objects and the functions over those objects. The structure of DEMOS links and processes were the major contributors to the simplicity. The changes made to produce DEMOS/MP involved the internal structure of link, modification to parts of the kernel, and limited changes to the various system processes.

When processes wish to communicate, they must first establish communication. The stream mechanisms introduced in the Eighth Edition Unix system,1 which have now become part of AT&T's Unix System V2, provide a flexible way for processes to conduct an already‐begun conversation with devices and with each other: an existing stream connection is named by a file descriptor, and the usual read, write, and I/O control requests apply. Processing modules may be inserted dynamically into a stream connection, so network protocols, terminal processing, and device drivers separate cleanly. However, these mechanisms, by themselves, do not provide a general way to create channels between processes. Simple extensions provide new ways of establishing communication. In our system, the traditional Unix IPC mechanism, the pipe, is a cross‐connected stream. A generalisation of file‐system mounting associates a stream with a named file. When the file is opened, operations on the file are operations on the stream. Open files may be passed from one process to another over a pipe. These low‐level mechanisms allow construction of flexible and general routines for connecting local and remote processes.

This paper describes the fundamentals of the X-TREE Operating System (XOS), a system developed to investigate the effects of the X-TREE architecture on operating system design. It outlines the goals and constraints of the project and describes the major features and modules of XOS. Two concepts are of special interest: The first is demand paging across the network of nodes and the second is separation of the global object space and the directory structure used to reference it. Weaknesses in the model are discussed along with directions for future research.