This paper describes a symmetrical distributed operating system (MOS) that has been running, since 1983, on PDP-11 computers interconnected by a 10 Mbps ProNET. The system is application code compatible with UNIX (Version 7) and uses the procedure call style of communications (as opposed to message passing). As such, it is similar to LOCUS but the internal structures of the two system are very different. The MOS kernel uses the layering technique with information hiding from module to module. It also provides “funnels,” whereby large amounts of data can be transferred between the kernel and user address spaces efficiently.

The main goals of MOS are network transparency, site autonomy and decentralized control leading to high availability, and dynamic load balancing through process migration. The last feature is rare among existing systems.

This is an interesting paper, though many technical details, such as process migration and decentralized control, are not described in any detail. Also, performance penalties due to information hiding and remote communications are not discussed at all. Nevertheless, the structure of the kernel is reasonable and its compatibility with UNIX should be of interest to people wishing to exte- nd their single-machine UNIX systems to an integrated distributed system.