Incompatible Timesharing System

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What Does Incompatible Timesharing System Mean?

Incompatible Timesharing System (ITS) is an early operating system written in assembly language. It was developed chiefly by the Artificial Intelligence Laboratory with input from the seminal Project MAC at the Massachusetts Institute of Technology (MIT). ITS supports Programmed Data Processor-6 and Programmed Data Processor-10.


Both ITS and the applications developed on it were influential in terms of their technical impact.Some of the important applications developed on ITS were EMACS and GNU information. Some programming languages like MacLisp (the precursor of Zeta lisp and common Lisp), Micro Planner, MDL and Scheme were also developed on ITS. ITS was also a crucial factor in the development of the hacker culture, which arose within MIT’s computer culture in the 1960s.

Techopedia Explains Incompatible Timesharing System

The ITS OS was developed in late 1960s and continued to be used up to 1990 at MIT, and until 1995 at the Stacken Computer Club in Sweden.

Some of the important technical features of ITS are as follows:

  • The operating system contained the first device-independent graphics terminal output. The screen content was controlled using generic commands created by a program. The content was usually translated into a sequence of device-dependent characters defined by the terminal the programmer was using.
  • Virtual devices were supported in software run in user processes called jobs.
  • It provided inter-machine file system access and was the first OS to include this feature.
  • It provided a sophisticated process management in which the processes were organized in a tree. Any process could be transparently frozen or restarted at any point in time.
  • A highly advanced software interrupt facility was provided, which could operate asynchronously.
  • It supported real-time and time-sharing operations, which worked simultaneously.

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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.