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The Beginnings of MIT: Reminiscences on the History of Time-Sharing

IP.com Disclosure Number: IPCOM000129706D
Original Publication Date: 1992-Mar-31
Included in the Prior Art Database: 2005-Oct-06
Document File: 8 page(s) / 36K

Publishing Venue

Software Patent Institute

Related People

John McCarthy: AUTHOR [+2]

Abstract

At the time of our interviews with the CUSS and Project MAC pioneers, we invited John McCarthy to join the group which provided this record following the 25th anniversary celebrations of the founding of the Laboratory of Computer Science. McCarthy was unable to extend his stay in the Cambridge area but graciously wrote his own memories of this era. I remember thinking about time-sharing at the time of my first contact with computers and being surprised that this was not the goal of IBM and all the other manufacturers and users of computers. This might have been around 1955. By time-sharing, I meant an operating system that permits each user of a computer to behave as though he were in sole control of a computer, not necessarily identical with the machine on which the operating system is running. Christopher Strachey may well have been correct in saying in his letter to Donald Knuth* [Footnote] * See Strachey's response to Knuth in the previous section. that the term was already in use for time-sharing among programs written to run together. This idea had already been used in the SAGE system. I do not know how this kind of time-sharing was implemented in SAGE. Did each program have to be sure to return to an input polling program or were there interrupts? Who invented interrupts anyway?** [Footnote] ** Alan Scherr reported that the patents on interrupt-driven I/O are held by three IBM researchers. I thought of them, but I do not believe I mentioned the idea to anyone before I heard of them from other sources.

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THIS DOCUMENT IS AN APPROXIMATE REPRESENTATION OF THE ORIGINAL.

Copyright ©; 1992 by the American Federation of Information Processing Societies, Inc. Used with permission.

The Beginnings of MIT: Reminiscences on the History of Time-Sharing

John McCarthy

At the time of our interviews with the CUSS and Project MAC pioneers, we invited John McCarthy to join the group which provided this record following the 25th anniversary celebrations of the founding of the Laboratory of Computer Science. McCarthy was unable to extend his stay in the Cambridge area but graciously wrote his own memories of this era.

I remember thinking about time-sharing at the time of my first contact with computers and being surprised that this was not the goal of IBM and all the other manufacturers and users of computers. This might have been around 1955.

By time-sharing, I meant an operating system that permits each user of a computer to behave as though he were in sole control of a computer, not necessarily identical with the machine on which the operating system is running. Christopher Strachey may well have been correct in saying in his letter to Donald Knuth*1 that the term was already in use for time-sharing among programs written to run together. This idea had already been used in the SAGE system. I do not know how this kind of time-sharing was implemented in SAGE. Did each program have to be sure to return to an input polling program or were there interrupts? Who invented interrupts anyway?**2 I thought of them, but I do not believe I mentioned the idea to anyone before I heard of them from other sources.

My first attempts to do something about time-sharing were in the fall of 1957 when I came to the MIT Computation Center on a Sloan Foundation fellowship from Dartmouth College. It was immediately clear to me that timesharing the IBM 704 would require some kind of interrupt system. I was very shy of proposing hardware modifications, especially as I did not understand electronics well enough to read the logic diagrams. Therefore, I proposed the minimal hardware modification I could think of. This involved installing a relay so that the 704 could be put into trapping mode by an external signal. It was also proposed to connect the sense switches on the console in parallel with relays that could be operated by a Flexowriter.

When the machine went into trapping mode, an interrupt to a fixed location would occur the next time the machine attempted to execute a jump instruction (then called a transfer). The interrupt would occur when the Flexowriter had set up a character in a relay buffer. The interrupt program would then read the character from the sense switches into a buffer, test whether the buffer was full, and if not return to the interrupted program. If the buffer was full, the program would store the current program on the drum and read in a program to deal with the buffer.

  (Image Omitted: John McCarthy's 1959 memorandum To: Professor P.M. Morse From:...