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 and remote-console efforts which are being developed by groups elsewhere. The only other general purpose time-sharing system known to be operating presently, that of the Bolt, Beranek and Newman Corporation for the PDP-1 computer, was recently described by Professor John McCarthy at the 1963 Spring Joint Computer Conference. Other time-sharing developments are being made at the Carnegie Institute of Technology with a G20 computer, at the University of California at Berkeley with a 7090, at the Rand Corporation with Johnniac,and at MIT (by Professor Dennis) with a PDP-1. Several systems resemble our own in their logical organization; they include the independently developed BBN system for the PDP-1, the recently initiated work at IBM (by A. Kinslow) on the 7090 computer, and the plans of the System Development Corporation with the Q32 computer.

To establish the context of the present work, it is informative to trace the development of time-sharing at MIT. Shortly after the first paper on time-shared computers, by C. Strachey at the June 1959 UNESCO Information Processing Conference, H. M. Teager and J. McCarthy at MIT delivered an unpublished paper "Time-Shared Program Testing" at the August 1959 ACM Meeting. Evolving from this start, much of the time-sharing philosophy embodied in the CTSS system has been developed in conjunction with an MIT preliminary study committee (initiated in 1960), and a subsequent working committee. The work of the former committee resulted, in April 1961, in an unpublished (but widely circulated) internal report. Time-sharing was advocated by J. McCarthy in his lecture, given at MIT, contained in "Management and the Computer of the Future" (MIT, 1962). Further study of the design and implementation of man-computer interaction systems is being continued by a recently organized institute-wide project under the direction of Professor Robert M. Fano. In November 1961 an experimental time-sharing system, which was an early version of CTSS, was demonstrated at MIT, and in May 1962 a paper describing it was delivered at the Spring Joint Computer Conference.

As might be expected, the detailed design and implementation of the present CTSS system is largely a team effort with the major portions vi