Compatible Time-Sharing System

The Compatible Time-Sharing System (CTSS) was the first general purpose time-sharing operating system.[2][3] Compatible Time Sharing referred to time sharing which was compatible with batch processing; it could offer both time sharing and batch processing concurrently.

Compatible Time-Sharing System (CTSS)
Preamble of two versions of the CTSS scheduler, one in MAD and one in FAP
DeveloperMIT Computation Center, Project MAC
Written inFAP assembly, MAD
Working stateDiscontinued, simulator available
Source modelOpen source
Initial release1961; 63 years ago (1961)
Marketing targetColleges and universities[1]
Available inEnglish
PlatformsIBM 7090, IBM 7094
Kernel typeMonolithic, protected
user interface
Command-line interface
License[data missing]
Succeeded byMultics

CTSS was developed at the MIT Computation Center ("Comp Center"). CTSS was first demonstrated on MIT's modified IBM 709 in November 1961. The hardware was replaced with a modified IBM 7090 in 1962 and later a modified IBM 7094 called the "blue machine" to distinguish it from the Project MAC CTSS IBM 7094. Routine service to MIT Comp Center users began in the summer of 1963 and was operated there until 1968.

A second deployment of CTSS on a separate IBM 7094 that was received in October 1963 (the "red machine") was used early on in Project MAC until 1969 when the red machine was moved to the Information Processing Center[4] and operated until July 20, 1973. CTSS ran on only those two machines; however, there were remote CTSS users outside of MIT including ones in California, South America, the University of Edinburgh and the University of Oxford.[1][5]

History edit

John Backus said in the 1954 summer session at MIT that "By time sharing, a big computer could be used as several small ones; there would need to be a reading station for each user".[6] Computers at that time, like IBM 704, were not powerful enough to implement such system, but at the end of 1958, MIT's Computation Center nevertheless added a typewriter input to its 704 with the intent that a programmer or operator could "obtain additional answers from the machine on a time-sharing basis with other programs using the machine simultaneously".[7]

In June 1959, Christopher Strachey published a paper "Time Sharing in Large Fast Computers" at the UNESCO Information Processing Conference in Paris, where he envisaged a programmer debugging a program at a console (like a teletype) connected to the computer, while another program was running in the computer at the same time.[8][9] Debugging programs was an important problem at that time, because with batch processing, it then often took a day from submitting a changed code, to getting the results. John McCarthy wrote a memo about that at MIT, after which a preliminary study committee and a working committee were established at MIT, to develop time sharing. The committees envisaged many users using the computer at the same time, decided the details of implementing such system at MIT, and started the development of the system.

Experimental Time Sharing System edit

By July, 1961[10] a few time sharing commands had become operational on the Computation Center's IBM 709, and in November 1961, Fernando J. Corbató demonstrated at MIT what was called the Experimental Time-Sharing System. On May 3, 1962, F. J. Corbató, M. M. Daggett and R. C. Daley published a paper about that system at the Spring Joint Computer Conference.[11] Robert C. Daley, Peter R. Bos and at least 6 other programmers implemented the operating system, partly based on the Fortran Monitor System.

The system used an IBM 7090, modified by Herbert M. Teager, with added 3 Flexowriters for user consoles, and maybe a timer. Each of the 3 users had two tape units, one for the user's file directory, and one for dumping the core (program in memory). There was also one tape unit for the system commands, there were no disk drives. The memory was 27 k words (36-bit words) for users, and 5 k words for the supervisor (operating system). The input from the consoles was written to the buffers in the supervisor, by interrupts, and when a return character was received, the control was given to the supervisor, which dumped the running code to the tape and decided what to run next. The console commands implemented at the time were login, logout, input, edit, fap, mad, madtrn, load, use, start, skippm, listf, printf, xdump and xundump.[citation needed]

This became the initial version of the Compatible Time-Sharing System. This was apparently the first ever public demonstration of time-sharing; there are other claims, but they refer to special-purpose systems, or with no known papers published. The "compatibility" of CTSS was with background jobs run on the same computer, which generally used more of the compute resources than the time-sharing functions.

Applications edit


The first version of the DOTSYS braille translation software ran on CTSS and could output to a BRAILLEMBOSS braille page printer.[12][13] DOTSYS on CTSS was first demonstrated on August 18, 1966, as part of a feasibility study where teletypesetter tape, in the form of news, was converted to Grade 2 Braille. The following month the feasibility of converting textbook information on teletypesetter tape to error-free Grade 2 Braille was successfully demonstrated.[14] As MIT CTSS was an academic system, a research vehicle and not a system for commercial computing, two years later a version of DOTSYS stripped of CTSS dependencies for software portability was used on an IBM 709 at the American Printing House for the Blind to print the first braille edition of a book produced from teletypesetter input, only a few weeks after the ink-print version.[15] The following year, on CTSS, a demonstration of printing mathematical tables in braille was shown. A short FORTRAN II program was written to produce a conversion table from inches to millimeters in braille via the BRAILLEMBOSS braille page printer.[16]

Intrex edit

Diagram of the Intrex running on CTSS

The Intrex Retrieval System ran on CTSS. Intrex was an experimental, pilot-model machine-oriented bibliographic storage and retrieval system with a database that stored a catalog of roughly 15,000 journal articles. It was used to develop and test concepts for library automation.[17][18][19] A deployment of three BRISC CRT consoles for testing at the MIT Engineering Library showed that it was preferred over two other systems, ARDS and DATEL.[20]

Features edit

Implementation edit

Kernel edit

CTSS used a modified IBM 7090 mainframe computer[27] that had two 32,768 (32K) 36-bit-word banks of core memory instead of the default configuration which provides only one.[28][29] One bank was reserved for the time-sharing supervisory program, the other for user programs. CTSS had a protected-mode kernel; the supervisor's functions in the A-core (memory bank A) could be called only by software interrupts, as in modern operating systems. Causing memory-protection interrupts were used for software interrupts.[8] Processor allocation scheduling with a quantum time unit 200 ms, was controlled by a multilevel feedback queue.[28] It also had some special memory-management hardware,[30] a clock interrupt,[31] and the ability to trap certain instructions.[30]

Supervisor subroutines edit

  • RDFLXA – Read an input line from console
  • WRFLX – Write an output line to console
  • DEAD – Put the user into dead status, with no program in memory
  • DORMNT – Put the user into dormant status, with program in memory
  • GETMEM – Get the size of the memory allocation
  • SETMEM – Set the size of the memory allocation
  • TSSFIL – Get access to the CTSS system files on the disk
  • USRFIL – Change back to user's own directory
  • GETBRK – Get the instruction location counter at quit

Programming languages edit

CTSS at first had only an assembler, FAP, and a compiler, MAD. Also, Fortran II code could be translated into MAD code by using MADTRN. Later half of the system was written in MAD. Later there were other programming languages including COMIT II, LISP 1.5 and a version of ALGOL.

File system edit

Each user had their own directory, and there were also shared directories for groups of people with the same "problem number". Each file had two names, the second indicating its type as did the extension in later system. At first, each file could have one of four modes: temporary, permanent, read-only class 1, and read-only class 2. Read-only class 1 allowed the user to change the mode of the file. Files could also be symbolically linked between directories. A directory listing by listf:

5/20/63		MAIN	MAD	P	15
5/17/63 	DPFA	SYMTB	P	1
5/17/63 	DPFA	BSS	P	1
5/17/63 	DPFA	FAP	P	2

Peripherals edit

Input-output hardware was mostly standard IBM peripherals. These included six data channels connecting to:

  • Printers, punched card readers and punches
  • IBM 729 tape drives, an IBM 1301 disk storage, later upgraded to an IBM 1302, with 38 million word capacity
  • An IBM 7320 drum memory with 186K words that could load a 32K-word memory bank in one second (later upgraded to 0.25 seconds)
  • Two custom high-speed vector graphics displays[32]
  • An IBM 7750 transmission control unit capable of supporting up to 112 teleprinter terminals, including IBM 1050 Selectrics and Model 35s. Some of the terminals were located remotely, and the system could be accessed using the public Telex and TWX networks.

Influences edit

CTSS was described in a paper presented at the 1962 Spring Joint Computer Conference, and greatly influenced the design of other early time-sharing systems.

Maurice Wilkes witnessed CTSS and the design of the Titan Supervisor was inspired by that.[33][34]

Dennis Ritchie wrote in 1977 that UNIX could be seen as a "modern implementation" of CTSS.[35] Multics, which was also developed by Project MAC, was started in the 1960s as a successor to CTSS – and in turn inspired the development of Unix in 1969. One of the technical terms inherited by these systems from CTSS is daemon.

Incompatible Timesharing System (ITS), another early, revolutionary, and influential MIT time-sharing system, was produced by people who disagreed with the direction taken by CTSS, and later, Multics; the name was a parody of "CTSS", as later the name "Unix" was a parody of "Multics".[36] CTSS and ITS file systems have a number of design elements in common. Both have an M.F.D. (master file directory) and one or more U.F.D. (user file directories). Neither of them have nested directories (sub-directories). Both have file names consisting of two names which are a maximum of six-characters long. Both support linked files.[5]

See also edit

References edit

  1. ^ a b c d Walden, David; Van Vleck, Tom, eds. (2011). "Compatible Time-Sharing System (1961-1973): Fiftieth Anniversary Commemorative Overview" (PDF). IEEE Computer Society. Retrieved February 20, 2022.
  2. ^ Noren, Allen (April 10, 2009). "An Interview with Brian Kernighan: Breeding Little Languages". O'Reilly Community. Archived from the original on June 30, 2017. Retrieved July 28, 2023. I was using CTSS, the first time-sharing system
  3. ^ Singh, Jai P.; Morgan, Robert P. (October 1971). Educational Computer Utilization and Computer Communications (PDF) (Report). St. Louis, MO: Washington University. p. 13. National Aeronautics and Space Administration Grant No. Y/NGL-26-008-054. Retrieved March 8, 2022. Much of the early development in the time-sharing field took place on university campuses.8 Notable examples are the CTSS (Compatible Time-Sharing System) at MIT, which was the first general purpose time-sharing system...
  4. ^ "New Information Center Will Open at MIT Today". The New York Times. November 11, 1968.
  5. ^ a b c Crisman, Patricia A., ed. (December 31, 1969). The Compatible Time-Sharing System, A Programmer's Guide (PDF) (Second ed.). The M.I.T Computation Center. Retrieved March 10, 2022.
  6. ^ Backus, John (1954). Digital Computer Advanced Coding Techniques (PDF). MIT. pp. 16-2–16-3. The first known description of computer time-sharing.
  7. ^ Progress Report Number 4 of the Research and Educational Activities in Machine Computation by the Cooperating Colleges of New England (Report). December 1958.
  8. ^ a b F. J. Corbató; M. M. Daggett; R. C. Daley; R. J. Creasy; J. D. Hellwig; R. H. Orenstein; L. K. Korn (1963). The Compatible Time-Sharing System A Programmer's Guide (PDF). MIT Press. ISBN 978-0-262-03008-3. Describe the system and its commands
  9. ^ John McCarthy (1983). "Reminiscences on the History of Time Sharing". Stanford University.
  10. ^ Progress Report Number 9 of the Research and Educational Activities in Machine Computation by the Cooperating Colleges of New England (Report). July 1961.
  11. ^ Corbató, Fernando J.; Merwin Daggett, Marjorie; Daley, Robert C. (May 3, 1962). "An Experimental Time-Sharing System". Archived from the original on September 6, 2009. Retrieved February 25, 2022.
  12. ^ Mann, Robert W (October 1986). "Selected Perspectives on a Quarter Century of Rehabilitation Engineering". Journal of Rehabilitation Research and Development. 23 (4): 1–6. PMID 3820117. Retrieved March 13, 2022. The modular software program for braille translation and automatic management of input and output modes, subsequently called "DOTSYS" was underway...
  13. ^ Dalrymple, George F. (February 26, 1973). "Final Report Development and Demonstration of Communication Systems for the Blind and Deaf/Blind. Braille Communication Terminals and Tactile Paging Systems" (PDF). The Sensory Aids Evaluation and Development Center Massachusetts Institute of Technology. Retrieved March 13, 2022.
  14. ^ Evaluation and Development of Sensory Aids and Devices. Final Report (PDF) (Report). The Sensory Aids Evaluation and Development Center Massachusetts Institute of Technology. April 3, 1967. Retrieved March 13, 2022. Demonstration on CTSS of teletypesetter-to-Grade 2 Braille
  15. ^ Final Report to Social Rehabilitation Administration Department of Health, Education and Welfare Washington, D.C. (PDF) (Report). The Sensory Aids Evaluation and Development Center Massachusetts Institute of Technology. April 30, 1969. Retrieved March 13, 2022. These programs, originally written to operate on the CTSS system at M.I.T., were modified for the 709 at the American Printing House for the Blind. This involved rewriting those parts of the programs which were CTSS-dependent.
  16. ^ Conversion Table, Inches to Millimeters a Braille Computer Generated Mathematical Table (PDF) (Report). The Sensory Aids Evaluation and Development Center Massachusetts Institute of Technology. August 14, 1970. Retrieved March 13, 2022.
  17. ^ Overhage, Carl F. J. (1971). Project Intrex - A Brief Description (PDF). ERIC (Report). MIT. Retrieved March 8, 2022.
  18. ^ Kehr, James E. (September 1972). Intrex Buffer-Controller Display System Operation and Software (PDF). ERIC (Report). MIT. Retrieved March 8, 2022.
  19. ^ Hurlburt, Charles E. (September 15, 1971). The Intrex Retrieval System Software (PDF). ERIC (Report). MIT. Retrieved March 8, 2022.
  20. ^ Overhage, Carl F. J. (March 15, 1972). Project Intrex. Semiannual Activity Report, 15 September 1971 - 15 March 1972 (PDF). ERIC (Report). MIT. Intrex PR-13. Retrieved March 17, 2022. Since September 27, 1971, the BRISC has been available at the Engineering Library station on a two-hours a day basis.
  21. ^ McMillan, Robert (27 January 2012). "The World's First Computer Password? It Was Useless Too". Wired magazine. Retrieved 22 March 2019.
  22. ^ Hunt, Troy (26 July 2017). "Passwords Evolved: Authentication Guidance for the Modern Era". Retrieved 22 March 2019.
  23. ^ Tom Van Vleck's memoir of The History of Electronic Mail
  24. ^ Fetter, Mirko (2019). New Concepts for Presence and Availability in Ubiquitous and Mobile Computing. University of Bamberg Press. p. 38. ISBN 978-3-86309-623-6. The basic concept of sending instantaneously messages to logged in users came with ... CTSS ...
  25. ^ Pouzin, Louis. "The Origin of the Shell". Multicians. Retrieved February 17, 2022.
  26. ^ Raymond, Eric S. (2003). The Art of UNIX Programming. Boston: Pearson Education. p. 234. ISBN 978-0-13-246588-5.
  27. ^ "Documents describing special hardware for CTSS".
  28. ^ a b Silberschatz, Abraham; Peterson, James L. (June 1988). "13: Historical Perspective". Operating System Concepts. Addison-Wesley. p. 514. ISBN 0-201-18760-4.
  29. ^ IBM 7090 and 7094 Data Processing Systems Additional Core Storage - RPO E02120 (7090) Dr RPO E15724 (7094) (PDF). Special Systems Features Bulletin. IBM. L22-6636-1.
  30. ^ a b IBM 7090-7094 Multiprogramming Package RPO E07291 (7090) or RPO 880287 (7094) (PDF). Special Systems Features Bulletin. IBM. L22-6641-3.
  31. ^ Core Storage Clock and Interval Timer - RPO FB9349 (PDF). Special Systems Features Bulletin. IBM. L22-6554-1.
  32. ^ Thornhill, D. E.; Stoz, R. H.; Ross, T. T.; Ward, J. E. (1968). "An Integrated Hardware-Software System for Computer Graphics in Time Sharing" (PDF). MIT Project MAC. ESL-R-356 and MAC-TR-56. Retrieved February 20, 2022. Console facilities include hardware projection of three-dimensional line drawings, automatic light pen tracking, and a flexible set of knob, switch, and push-button inputs. The console is attached to the Project MAC IBM 7094 Compatible Time-Sharing System either directly or through a PDP-7 Computer.
  33. ^ Hartley, David (2004). "The Titan Influence". Computer Systems. Springer. pp. 103–108. CiteSeerX ISBN 978-0-387-21821-2. Sir Maurice, as he is known today, had been inspired by CTSS to create a time-sharing system
  34. ^ Fraser, Sandy (2004). "An Historical Connection between Time-Sharing and Virtual Circuits". Computer Systems. Springer. pp. 85–88. CiteSeerX ISBN 978-0-387-21821-2. Maurice Wilkes discovered CTSS on a visit to MIT in about 1965, and returned to Cambridge to convince the rest of us that time-sharing was the way forward
  35. ^ Ritchie, Dennis M. (1977). The Unix Time-sharing System: A retrospective (PDF). Tenth Hawaii International Conference on the System Sciences.
  36. ^ Levy, Steven (2010). "Winners and Losers". Hackers: Heroes of the Computer Revolution - 25th Anniversary Edition (1st ed.). Sebastopol, California: O'Reilly Media. pp. 85–102. ISBN 978-1-4493-8839-3.

Further reading edit

External links edit