Compatible Time-Sharing System
| Developer | MIT's Computation Center |
|---|---|
| Written in | FAP assembly, MAD |
| Working state | Discontinued, Simulator |
| Initial release | 1961 |
| Marketing target | MIT only |
| Available in | English |
| Platforms | modified IBM 7094 |
| Kernel type | monolithic, protected |
| Default user interface | command line |
| License | open source |
| Official website | www |
The Compatible Time-Sharing System (CTSS), was one of the first time-sharing operating systems; it was developed at Massachusetts Institute of Technology's Computation Center. CTSS was first demonstrated in 1961, and was operated at MIT until 1973. During part of this time, MIT's influential Project MAC also ran CTSS, but the system did not spread beyond these two sites.
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.
The "Compatible" in the name refers to backward compatibility with the standard batch processing OS for the IBM 7094, the FORTRAN Monitor System (FMS). CTSS ran an unaltered copy of FMS, processing a standard batch stream, in a pseudo-virtual 7094 provided by its background facility. (The hardware was partly but not fully virtualized; see History of CP/CMS for further details.) Background FMS jobs could access tapes normally, but could not interfere with foreground time-sharing processes or the resources used to support them.
CTSS was very influential. It showed that time-sharing was viable; it fostered important new applications for computers; it had a significant influence on the next generation of time-sharing systems, notably CP/CMS. CTSS and its direct successor, Multics, pioneered many core concepts of current operating systems.
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". But computers at that time, like IBM 704, were not powerful enough to implement such system. 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. 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.
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