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ITS development was initiated in the late 1960s by those (notably the majority of the AI Lab at that point in time) who disagreed with the direction taken by Project MAC's Multics project (which had started in the mid 1960s), particularly such decisions as the inclusion of powerful system security. The name was a hack on the earliest MIT time-sharing operating system, the Compatible Time-Sharing System, which dated from the early 1960s.

ITS was initially developed for the Digital Equipment Corporation PDP-6 computer, and later moved to the PDP-10 once it became available, where it saw the majority of its development and use.

Among numerous interesting features and oddities, the ITS top-level command interpreter was the PDP-10 machine language debugger ( DDT), whose commands looked like line noise to the unitiated.

Its main editor for many years, TECOTECO (pronounced /tee'koh/; originally an acronym for paper] T ape E ditor and CO rrector but later T ext E ditor and CO rrector was a text editor developed at MIT in the 1960s and modified by 'just about everybody'. With all the dialects included, TECO m, was programmable in a similar-looking gibberish. The EMACS editor is a descendant of a collection of TECO macros, now much developed.

Among other significant and influential software subsystems which were developed on ITS, the MacsymaMacsyma is a computer algebra system that was originally developed from 1967 to 1982 at the MIT AI Lab as part of Project MAC. In 1982, MIT submitted a copy of Macsyma to the United States Department of Energy, which was one of the major funders of Macsym symbolic algebra system is probably the most important; the GNUFor the African animal gnu see wildebeest. logo Believed to be the original artwork of Etienne Suvasa GNU is a recursive acronym for "GNU's Not Unix". The GNU project was launched in 1983 by Richard Stallman with the goal of creating a complete operating INFO help system used in LinuxThis article is about Linux-based operating systems, GNU/Linux, and related topics. See Linux kernel for the kernel itself. See Linux (washing powder) for the Swiss brand of washing powder. Tux, a plump penguin, is the official Linux mascot Linux is the n, some versions of UNIX, and EMACS was also started on ITS.

1 Significant technical features

ITS was an operating system with many revolutionary features; for some significant ones, it was the first to deploy them. Among them were:

• It had the first device-independent graphics terminal output; programs generated generic commands to control screen content, which the system automatically translated into the appropriate character sequences for the particular type of terminal operated by the user.

• A general and powerful mechanism for implementing virtual devices in software which ran in user processes (which were called "jobs" in ITS).

• Using this mechanism, it provided transparent inter-machine filesystem access (almost certainly the first operating system to do so). The ITS machines were all connected to the ARPAnet, and a user on one could perform any operation on a file on one of the other machines that they could on files on the local machine.

• Sophisticated process management; user processes were organized in a tree hierarchy, and a superior process could control a large number of inferior processes. Any inferior process could be frozen at any point in its operation, and any of its state (including contents of the registers) examined; the process could then be restarted without any problems. (This facility is now in one of the GNUFor the African animal gnu see wildebeest. logo Believed to be the original artwork of Etienne Suvasa GNU is a recursive acronym for "GNU's Not Unix". The GNU project was launched in 1983 by Richard Stallman with the goal of creating a complete operating tools.)

• An advanced software interrupt facility that allowed user processes to operate asynchronously, using complex interrupt handling mechanisms.

• PCLSRing, a powerful and subtle mechanism which provided what appeared (to user processes) to be non-blocking, safely interruptible system calls. No process could ever observe any process (including itself) in the middle of executing any system call.

Many of these, and numerous other significant advances, were later picked up by other operating systems.