LOCUS is a discontinued distributed operating system developed at UCLA during the 1980s.
This provided particularly good access times for files that were read more often than they were written, the normal case for directories for example.
For example, it was possible to build a LOCUS cluster containing both PDP-11/45 and VAX 750 machines, but instruction sets used were not identical, so two versions of each object program would be needed[note 1] The solution was to replace the files that needed to be different on a per node basis by special hidden directories.
Both the Unix fork and exec calls would examine an advice list which determined on which node the process would be run.
[note 2] Processes could use pipes for inter node communication, including named pipes, The LOCUS system was designed to be able to cope with network partitioning - one or more nodes becoming disconnected from the rest of the system.