Incompatible Timesharing System

ITS, the Incompatible Timesharing System, was another early, revolutionary, and influential MIT time-sharing operating system; it was developed principally by the Artificial Intelligence Laboratory at MIT, with some help from Project MAC.

It was the system with the first full inter-computer shared file access, the first device-independent graphics terminal output, and numerous other significant advances.

Among countless other oddities, its top-level command interpreter was a debugger (DDT) whose commands looked like line noise, and its main editor, TECO, was programmable in a similar-looking gibberish.

ITS was developed on the Digital Equipment Corporation PDP-6 and PDP-10 mainframe computers.

ITS was produced by people who disagreed with the direction taken by Multics; the name was a hack on CTSS.

Further Reading

• Donald E. Eastlake, ITS Reference Manual, Version 1.5, (MIT AI Laboratory, 1969) documents a very early version of the system (Warning, very large file, scanned page images)
• Donald E. Eastlake, ITS Status Report (MIT AI Laboratory, 1972)

• http://www.cosmic.com/u/mirian/its/ if you're crazy enough to want to run it on a PDP-10 simulator
• http://www.its.os.org/ contains file system images of various ITS machines, including documentation of the final system