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Source Code for CTSS released
Mainframes ROCK! writes "The source code for the Compatible Time-Sharing System, CTSS, has been released, and the here is the source code. CTSS was one of the first time-sharing operating systems and a direct ancestor of Linux. Developed at MIT in the 1960's on a specially modified IBM 7094 system.; it was developed at Project MAC at MIT. CTSS was first published, as well as operated in a time-sharing environment, in 1961; in addition, it was the system with the first computerized text formatting utility, and one of the very first to have inter-user electronic mail."
...is on RubyForge right here.
It's 400K lines of assembly code... what could be sweeter?
The Army reading list
REMINISCENCES ON THE HISTORY OF TIME SHARING
John McCarthy, Stanford University
1983 Winter or Spring
I remember thinking about time-sharing about the time of my first contact with computers and being surprised that this wasn't 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 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 don't 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? I thought of them, but I don't believe I mentioned the idea to anyone before I heard of them from other sources.
My first attempts to do something about time-sharing was in the Fall of 1957 when I came to the M.I.T. Computation Center on a Sloan Foundation fellowship from Dartmouth College. It was immediately clear to me that the time-sharing the IBM 704 would require some kind of interrupt system. I was very shy of proposing hardware modifications, especially as I didn't 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 ccnsole in parallel with relays that could be operated by a Flexowriter (a kind of teletype based on an IBM typewriter).
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.
It was agreed (I think I talked to Dean Arden only.) to install the equipment, and I believe that permission was obtained from IBM to modify the computer. The connector to be installed in the computer was obtained.
However, at this time we heard about the "real time package" for the IBM 704. This RPQ (request for price quotation was IBM jargon for a modification to the computer whose price wasn't guaranteed), which rented for $2,500 per month had been developed at the request of Boeing for the purpose of allowing the 704 to accept information from a wind tunnel. Some element of ordinary time-sharing would have been involved, but we did not seek contact with Boeing. Anyway it was agreed that the real time package, which involved the possibility of interrupting after any instruction, would be much better than merely putting the machine in trapping mode. Therefore we undertook to beg IBM for the real time package. IBM's initial reaction was favorable, but nevertheless it took a long time to get the real time package - perhaps a year, perhaps two.
It was then agreed that someone, perhaps Arnold Siegel, would design the hardware to connect one Flexowriter to the computer, and later an installation with three would be designed. Siegel designed and build the equipment, the operating system was suitably modified (I don't remember by whom), and demonstration of on-line LISP was held for a meeting of the M.I.T. Industrial Affiliates. This demonstration, which I planned and carried out, had the audience in a fourth floor lecture room and me in the computer room an
CTSS (Compatible Time Sharing System) lent its name to MIT's ITS (Incompatible Time Sharing System) for the PDP-10.
I'm pretty sure it was ITS that RMS developed Emacs (Editor Macros, or Eight Megs and Constantly Swapping) on but he'd know for sure.
Also, from SAIL (Stanford Artificial Intelligence Laboratory) we got WAITS which was the West-coast Alternative to ITS.
MULTICS also grew out of these roots, and Unix of course is a play on "Multics".
Indeed, calling CTSS a DIRECT ancestor is a bit of a stretch. Dennis Ritchie is about as authoritative as you are going to get on the history of Unix and Unix is the direct ancestor of Linux. Read his article on the history of Unix. There you will find his quote in section 1.3 on just where CTSS comes into the genisis of Unix....it is a distant ancestor. The Wikipedia article on history of OS'es is strangely lame on this topic.
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