LOCUS

LOCUS is a discontinued distributed operating system developed at the University of California, Los Angeles during the 1980s. It was an early implementation of the single-system image idea, in which a cluster of machines appears to its users as one larger machine. Work ran at UCLA between 1980 and 1983, starting on a cluster of PDP-11/45 computers joined by ring networks and reaching 17 VAX-11/750 machines on a 10 megabit Ethernet by 1983, with support from an ARPA research contract. The system was Unix compatible and gave a single root view of the file system and one process space across all nodes. Files could be replicated on several nodes, with one node acting as the current synchronization site for each file system. Special hidden directories let a mixed cluster hold different program versions per processor type, and the system could keep working through a network partition and merge changes afterward. The Locus Computing Corporation commercialized these ideas, which passed into OSF/1 AD and the SCO-Tandem UnixWare NonStop Clusters product.