From the interview of Richard M. Stallman, I learned that when Richard Stallman joined the Artificial Intelligence Lab at Massachusetts Institute of Technology in 1971, the community of programmers (or say hackers) at AI Lab used to run a free operating system probably developed by themselves.

Now, from the history of Multics I learned that in early days of computers, (in 1960's) Time Sharing system, more precisely CTSS (Compatible Timesharing System) developed and later on (around 1965), Multics had been developed by joined effort of MIT, Bell Labs and GE. Group of developers moved from CTSS to Mutics at the end of 1968. Bell Labs withdrawn the development of Multics in April 1969 because of frustration but Ken Thompson (who earlier contributed in the development of Multics) started developing another system which called "Unix" in 1970.

So, I want to know which is the operating system and more importantly which is the kernel that hackers at MIT AI Lab used to run in 1971? Was it CTSS or Multics or newly developed Unix or something else developed by themselves?

P.S (History goes...) Later on, that operating system at AI Lab started to become non-free and free community died around 1982 which inspired stallman to start a new community for free software, GNU in 1983.


1 Answer 1


On the About GNU page of the GNU project, Richard Stallman himself states that the operating sysytem in use when he joined the MIT Artificial Intelligence (AI) Lab in 1971 was the Incompatible Timesharing System (ITS):

When I started working at the MIT Artificial Intelligence Lab in 1971, I became part of a software-sharing community that had existed for many years. Sharing of software was not limited to our particular community; it is as old as computers, just as sharing of recipes is as old as cooking. But we did it more than most.

The AI Lab used a timesharing operating system called ITS (the Incompatible Timesharing System) that the lab's staff hackers (1) had designed and written in assembler language for the Digital PDP-10, one of the large computers of the era. As a member of this community, an AI Lab staff system hacker, my job was to improve this system (...)

(1) The use of “hacker” to mean “security breaker” is a confusion on the part of the mass media. We hackers refuse to recognize that meaning, and continue using the word to mean someone who loves to program, someone who enjoys playful cleverness, or the combination of the two. See my article, On Hacking.

  • (my emphasis)

For more information about why the 'hackers' at MIT's AI lab felt they needed to invent a new time-sharing operating system, rather than using the CTSS system, or the Multics system then being developed by MIT's Project MAC, take a look at Chapter 6 in Steven Levy's Hackers: Heroes of the Computer Revolution, especially from p112.

  • Do you have any idea what inspired hackers to develop ITS when CTSS already existed?
    – Pandya
    Apr 20, 2019 at 9:24
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    @Pandya CTSS & Multics prevented them from working the way they wanted to (and in some cases, would not allow certain programs to run at all). Take a look at Chapter 6 in Steven Levy's ' Hackers: Heroes of the Computer Revolution, especially from p112. Apr 20, 2019 at 11:42
  • Yes, thanks for suggesting that book.
    – Pandya
    Apr 20, 2019 at 16:40
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    @Flux I think Pandya actually posted that question as a follow-up to this one. Apr 20, 2019 at 19:34
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    The accepted answer is correct. I just wanted to add that a copy of ITS from 1972 has been preserved, and it's possible to run it on a PDP-10 emulator to see what it was like. Sep 30, 2019 at 9:54

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