Interactive Application System

Interactive Application System, usually called IAS, was a Digital Equipment Corporation operating system for the PDP-11, forked from RSX-11D. It was designed around a mix of concurrent timesharing, real-time and batch work and could be run in three modes, Real-Time, Multi-User and Timesharing, with a heuristic timesharing scheduler that tracks the history of performance and degree of interaction. It kept the RSX-11 practice of putting a version number in a file identifier, offered two command language interpreters, the RSX-11 MCR and the Program Development System, which was an early implementation of the Digital Command Language, and distributed DEC's Sort/Merge utility. Version 3.0 began distribution in late 1979 and the final version, 3.4, appeared in May 1990.