•  On This Page


CTSS Programmer's Guide

Computation Center Memos about CTSS

Programming Staff Notes

CTSS Bulletins

Other CTSS documents

CTSS Source Programs


   •  Links to Other Sites

CTSS description at

Project MAC description at

Wikipedia's CTSS Entry

CTSS follow-on: Multics

MIT Archives

CTSS Documents

December 26, 2016


Most documentation of CTSS was produced and distributed on paper rather than on-line. The on-line documents on this website were located in paper form and scanned by several sources, primarily and the Multics History Project. In 2006, as part of the Multics History Project, Roger Roach and Olin Sibert undertook to scan everything related to both CTSS and Multics on the bookshelves and in the personal files of M.I.T. Professor Jerome Saltzer.

To provide authoritative answers to detailed questions, the last item below is a set of source program listings (retrieved from backup tapes) of the CTSS supervisor and the system-provided user commands.

In addition to these on-line documents there are presumably some CTSS materials in paper form held by the MIT Archives. That resource has not been explored.

The Compatible Time-Sharing System: A Programmer's Guide

MIT Press published two editions of the CTSS Programmer's Guide, both in paperback. Pre-publication copies of the 1963 first edition had a light brown cardstock cover. The published version, known as the "candy-stripe" edition, had a slick-coated bright red and white cover.

In 1966, after development of a new file system and many other features, a second edition of the Programmer's Guide was published in a green plastic cover. Inside the green cover the individual pages were perforated next to the binding and pre-punched so that they could be removed and placed in a three-ring binder to allow updating.

Computation Center Memos about CTSS

Long before CTSS was developed, the MIT Computation Center distributed a series of memoranda to communicate both internally and with users. When CTSS development began, memos about it were issued in this series, intermixed with many other computation-related topics. Once CTSS became a supported service use of this series was largely replaced by two new series, Programming Staff Notes and CTSS Bulletins, both described below. Of the 50-odd Computation Center Memos that pertained to CTSS, 19 were found in Professor Saltzer's files.

Programming Staff Notes

When CTSS became a public service in 1963 the MIT Computation Center began local distribution of a series of notes by and for those programming staff members who were developing the system. They were reproduced with a spirit duplicator (Ditto machine), a process of variable quality that combined with the passage of time has left some pages so light as to be unreadable.

The copy of the Programming Staff Notes that was scanned is the set that was found on Professor Saltzer's bookshelf in the spring of 2006. His set runs from PSN-01 (September 1963) to PSN-69 (February 1967). PSN-28 is missing and the series may have continued after PSN-69.

CTSS Bulletins

The series of CTSS Bulletins were used for communication with the CTSS user community starting in December 1963.

The copy of the CTSS Bulletins that was scanned is the set that was found on Professor Saltzer's bookshelf in the spring of 2006. His set runs from CB-01 (December 1963) to CB-88 (August 1966). CB-81, 82, 85, and 87 are missing and the series may have continued after CB-88.

Other CTSS documents

CTSS Source Programs

The programs that constitute CTSS were written in FAP, the Fortran Assembly Program for the 709/7090/7094, and MAD, the Michigan Algorithm Decoder, a higher-level language based on Algol 58. The available materials have been collected from three places and are in three different forms.

First is a set of assembler and compiler output listings of the programs of the CTSS supervisor and the system-provided user commands. The program listings were originally intended to be printed on a line printer with 132 fixed-width characters. These listing files appear to have been archived with the CTSS ARCHIV command into 24 separate archive files that were extracted from CTSS backup tapes made in 1970 (system MIT8B3) and 1972 (system MIT8C0). The archive files are ASCII text without compression and can be read with an ordinary text editor. For ease of downloading, the 24 archive files have been further combined into a single zip file that is about 6 megabytes in size.

Three essential FAP programs were not in those archives and were tracked down later. Two of them, named DAEMON and INIT, were used to set up the machine and initialize CTSS. The third, named COMC8G, contains LOGIN and several related privileged commands. INIT was located in paper form and scanned to PDF. All three are in the form of assembler output listings and have the secondary name ".txt" or ".pdf".

Finally, there are three CTSS archives of the original source programs that comprise the RUNOFF command. These programs are in 80-column card format with line numbers in columns 72-80 and have the secondary name ".txt".

Preservation Credits: The CTSS manuals were acquired from Scanning of CC Memos, PSNs, and CC Bulletins was done by the Multics History Project (Roger Roach and Olin Sibert). Mac-TR-16 was scanned by the Library 2000 project of the MIT Laboratory for Computer Science. The MAD manual was scanned by the University of Michigan Engineering Library. The CTSS 50th Anniversary Commemorative Overview by Dave Walden and Tom Van Vleck is a publication of the IEEE Computer Society. CTSS source file archives were retrieved from backup tapes by Paul Pierce and Paul Green.

Design credits: The CSAIL logo is a work-for-hire chosen by the CSAIL logo committee. The web page design and style were derived from the MIT Information Services & Telecommunications standard template.

Please send corrections, comments and suggestions to: