Compatible Time Sharing System

This article relates to the operating system of the MAC Project with MIT. CTSS can also mean CRAY Time Sharing System, distinct system developed for the Superordinateur S CRAY, or Cambridge Time Sharing System, developed for the host computers IBM.

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CTSS , which means C ompatible T ime- S haring S ystem (compatible system at time-sharing), is one of the first operating systems to Temps divided. It was developed by the Projet MAC with the MIT. First publication of CTSS, like its first use in an environment on time-sharing, date of 1961; it was moreover the first system to have a utility of formatting of computerized text (Runoff), and one of the first to propose a Email between users.

Although CTSS did not have a great influence from the point of view of the technical details, it had at least the major importance to show that the system of the time-sharing was viable, and to have for successor Multics, from of which all the modern operating systems result, at least in the spirit (to be started with UNIX and all its descent).

In addition to the email and the word processing, Louis Pouzin created a utility called RUNCOM for CTSS. This one took a whole of orders contained in a file and carried out them; it is the direct ancestor of the Script of interpreter of orders ( Shell script ). It also allowed the substitution of parameters.

CTSS used a host computer IBM 7094 modified (to allow the segmentation of the memory) which contained two banks of 32,768 words of main memory, instead of only one. One of the two banks was reserved for the monitoring program of the time-sharing, the other with the user's programs. CTSS also had a special material of management of memory, a switch of clock and faculty to stop certain instructions. The material of input/output primarily consisted of IBM peripherals. Inter alia, six channels of data were connected to:

of the printers and readers of perforated cards;
of the readers of bands IBM 729, a memory disc IBM 1301, replaced later by a IBM 1302, of a capacity of 38 million words;
a memory drum of 186.000 words which could charge in one second a bank with 32K with memory (this performance was then improved to 1/4 of second);
two vectorial graphic screens at high speed;
a control unit of transmission IBM 7750, able to support to 112 terminals in text mode, inter alia the Teleprinters IBM 1050, Selectric S and Model 35. Some of these terminals were located remotely and one could reach the system by telegraph networks public Telex and TWC.

CTSS was compatible with FORTRAN Monitor System (FMS), a computing system of Batch processing which turned on computer 7094 before the invention of CTSS. FMS could turn in background with almost as much effectiveness than without operating system. Turning to the background, FMS had access to certain units of magnetic bands and the bank user of 32 K main memory.

Multics, which was also developed by the MAC Project, started in the Années 1960 like successor of CTSS, in order to allow a future use in multiple access. Multics was the operating system which led to the development of Unix in 1970.

ITS, the I ncompatible T imesharing S ystem (incompatible system at time-sharing), another system at early, revolutionary time-sharing and of a great influence of MIT, was conceived by people who désappouvaient the orientation taken by Multics; the name was found by diverting that of CTSS, as later that of Unix diverted that of Multics.

See too

Fernando J. Corbató, chief of the project

Reference books

F.J. Corbató, Mr. Mr. Daggett, R.C. Daley, Experimental Year Time-sharing System (IFIPS 1962)
Robert Mr. Fano, The MAC System: At Progress report (MIT Project MAC, 1964) described the use of CTSS
Jerome H. Saltzer, CTSS Technical Notes (MIT Project MAC, 1965) described the internal characteristics of CTSS with some details
Jerome H. Saltzer, Manuscript Typing and Editing (MIT Center Computation, 1964) described the first system of formatting of text computerized

External bonds

John McCarthy, Reminiscences one the History off Time Sharing off presents the origins of the concept of time-sharing
The IBM 7094 and CTSS the attractive Memories of a programmer system on CTSS
The Origin the Shell describes the evolution of RUNCOM to the modern interpreter of orders
CTSS Source in the collection of Paul Pierce

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