 It runs on VMS on VAX and Alpha and on Tru64.UniPrise Systems, Inc., was responsible for the compiler;

In the late 1960s and early 1970s, many US and Canadian universities were establishing time-sharing services on campus and needed conversational compiler/interpreters for use in teaching science, mathematics, engineering, and computer science.Dartmouth were developing BASIC, but PL/I was a popular choice, as it was concise and easy to teach.