Computer systems consisting of many machines will be the norm within a few years. However, making a collection of machines appear as a single, coherent system - in which the location of files, servers, programs, or users is invisible to users who do not wish to know - is a very difficult problem. LOCUS, a distributed version of the popular operating system Unix, provides an excellent solution. It makes a collection of computers, whether they are workstations or mainframes, as easy to use as a single computer by providing a set of supports for the underlying network that is virtually invisible to users and - applications programs.