The trio operating system
Per Brinch Hansen, Jon Fellows · Software Practice and Experience · 1980
Abstract This paper is an overview of the Trio system which enables users to simultaneously develop and execute programs at three terminals. The system consists of an operating system written in Concurrent Pascal and a set of standard programs written in Sequential Pascal. The system has been used on a PDP 11/55 minicomputer since spring 1979. This work concludes 5 years of experience with the first abstract language for concurrent programming.