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  • 50th Anniversary of MIT's Compatible Time-Sharing System
  • David Walden (bio)

Time sharing was in the air around the Massachusetts Institute of Technology and Cambridge in the years surrounding 1961. MIT faculty, staff, and students who had worked directly with the Whirlwind or TX-0 computer sitting at their consoles wanted more of that interactive access. The then-traditional batch-processing computer system approach was slow for program debugging and was made worse by machine overloading as digital computing was becoming more popular. MIT professor John McCarthy had been articulating the argument for time-shared interactive computers for several years, including proposing modifications to MIT's IBM 704 to enable it. Professor Herb Teager proposed his own experiment with time sharing. J.C.R. Licklider and Ed Fredkin at Bolt Beranek and Newman (across town in Cambridge) had hired McCarthy as a consultant, and together they began designing a timesharing system for the PDP-1 computer. Professor Jack Dennis got another PDP-1 from Digital, and he collaborated with Fredkin and Ben Gurley of Digital about hardware modifications to support time sharing. And in the spring of 1961, Professor Fernando Corbató, then associate director of MIT's Computation Center, began to design a system he called the Compatible Time Sharing System (CTSS) for MIT's IBM 709 computer (that had replaced the 704).

Corbató initially worked with two of his Comp Center staff members, Robert Daley and Marjoire Merwin. They arranged for IBM to provide an interrupt capability for the machine that let them control the machine.

They created a special version of the operating system that set aside 5 kilowords of memory (32-kiloword total) for the time-sharing supervisor (and for buffering typewriter terminal input and output). They used tape drives to store the programs and files of the four terminals' users. It was crude, but that original configuration allowed a November 1961 demonstration of interactive computer use.1

Thus, 2011 is the 50th anniversary of the conception and initial demonstration of CTSS.2

Those initial CTSS demonstrations helped convince people at MIT of the value of time sharing. Over the next couple of years, the IBM 709 was upgraded to a 7090, a second 32-kiloword bank of memory was added to allow more space for the time-sharing system, and a disk auxiliary storage unit and controller for 32 terminals were added.3 The existence of CTSS also helped motivate J.C.R. Licklider (who by then had moved to ARPA) to fund the creation of MIT's famous Project MAC.4


Jean Carteron
Jean Carteron (1926-2011) was a central witness of and influential actor in the development of computing in France. Trained as a telecom engineer in the late 1940s, he established scientific computing at Electricité de France. In 1954, he was one of the few Frenchmen to visit Maurice

Wilkes' EDSAC team in Cambridge, UK, to learn about stored-program computers. In 1957, with other computer pioneers, he created the French learned society in this field, with its journal, Chiffres. Two years later, he was a key negotiator and organizer of the International Conference on Information Processing Societies, which was the founding event of IFIP. Carteron remained a French representative to IFIP until 1981.

He moved to the fast-growing sector of computer services in 1963, when he was appointed CEO of a new company within the SEMA group, to develop operating systems under contract. In 1969 he founded his own company, Steria, that he chaired until the end of the century, making it one of the leading computer service firms in Europe. In the 1990s, he supported computer history initiatives and wrote a book mixing his personal memoirs with the story of his company: Steria - 30 Ans de Création Continue [Steria: 30 Years of Cominuous Creation] (Le Cherche-Midi, 1991).

For a more detailed biography, see the Biographies department article from January-March 2010:

Pierre Mounier-Kuhn is a historian at CNRS and the Paris-Sorbonne University. Contact him at

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By 1963, CTSS was a stable, large...