Inventor of Compatible Time-Sharing System has passed away

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American computer scientist Fernando “Corby” Corbató has died at the age of 93. He worked at MIT on the Compatible Time-Sharing System, laying the foundation for many current OS features, including privacy.

Corbató was co-author of the 1961 document An experimental time-sharing system. He then worked as a research assistant at the Computation Center at the Massachusetts Institute of Technology, demonstrating the Compatible Time-Sharing System, or CTSS. This system can deploy resources for various processes and tasks, so that different users can work with a computer. That was a big difference from how computers had been used until then, where users gave punched tapes to operators, who then ran the program. CTSS built on the idea of ​​multiprogramming, where one program is already running the moment the other has to wait for an outcome.

In the demonstration, MIT’s team led by Corbató used an IBM 7090 connecting three Flexowriter teleprinters with two tape units each. The system was a breakthrough in efficiency for input, causing Corbató to write in his paper: “Once a user is used to the immediate response of the computer, delays of even a fraction of a minute are excruciatingly long.” According to him, that was an indication that programmers would be happy to use the system, if it were generally available.

When developing CTSS, Corbató was already confronted with the consequences of using the system by different users. In the design, users work independently of each other, but the pioneer recognized that it can be efficient if several consoles communicate with a single program. This can be seen as a vision of the emergence of independent, protected accounts on the one hand and a form of cloud computing with collaboration on documents on the other.

With that vision, Corbató worked on Multics after CTSS. That operating system written in PL/I was the first to have a hierarchical file system and a form of security management thanks to access control lists for files. Ken Thompson and Dennis Ritchie, among others, programmed for Multics and used their knowledge to develop their own, more compact system, whose name is related to Multics: Unix.

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