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The Dartmouth Time-Sharing System (DTSS) is an operating system first developed at Dartmouth College between 1963 and 1964. It was the first successful large-scale time-sharing system to be implemented, and was also the system for which the BASIC language was developed. DTSS was developed continually over the next decade and gave rise to the Multics effort, and thus indirectly, Unix. The system was finally shut down in 1999.

History

DTSS was inspired by a PDP-1-based time-sharing system at Bolt, Beranek and Newman. In 1962, John Kemeny and Thomas Kurtz at Dartmouth College submitted a grant for the development of a new time-sharing system to NSF (funded in 1964).^[1] Its implementation began in 1963, by a student team^[2] under the direction of Kemeny and Kurtz with the aim of providing easy access to computing facilities for all members of the college.^[3] On May 1, 1964, at 4:00 a.m., the system began operations. It remained in operation until the end of 1999.^[4][5] DTSS was originally implemented to run on a GE-200 series computer with a GE DATANET-30 as a terminal processor that also managed the 235. Later, DTSS was reimplemented on the GE 635,^[1] still using the DATANET-30 for terminal control. The 635 version provided interactive time-sharing to up to nearly 300 simultaneous users in the 1970s, a very large number at the time.

Background

Kemeny and Kurtz intended for students in technical and nontechnical fields to use DTSS. They arranged for the second trimester of the freshman mathematics class to include a requirement for writing and debugging four Dartmouth BASIC programs. By 1968, more than 80% of Dartmouth students had experience in computer programming. 80 classes included "official" computer use, including those in engineering, classics, geography, sociology, and Spanish.^[6] 57% of DTSS use was for courses and 16% for research. 27% was for casual use and entertainment, which the university stated "is in no sense regarded as frivolous";^[7] on the contrary, Kemeny and Kurtz were pleased to find that 40% of all faculty members—not just those in technical fields—used DTSS, and that many students continued using the system after no longer being required to. Kemeny wrote in a brochure describing the system that just as a student could enter the library and borrow a book without asking permission or explaining his purpose, "any student may walk into Kiewit Computation Center, sit down at a console, and use the time-sharing system. No one will ask if he is solving a serious research problem, doing his homework the easy way, playing a game of football, or writing a letter to his girlfriend".^[8]

Design

DTSS's design emphasized immediate feedback; Kemeny and Kurtz observed that "any response time which averages more than 10 seconds destroys the illusion of having one's own computer".^[6] Many DTSS users believed, by contrast, that their terminal was the computer.^[9] Because of the educational aims, ease of use was a priority in DTSS design. DTSS implemented the world's first Integrated Design Environment (IDE). Any line typed in by the user, and beginning with a line number, was added to the program, replacing any previously stored line with the same number; anything else was immediately compiled and executed. Lines which consisted solely of a line number weren't stored but did remove any previously stored line with the same number. This method of editing provided a simple and easy to use service that allowed large numbers of teleprinters as the terminal units for the Dartmouth Timesharing system. IDE commands included

• 
  CATALOG – to list previously named programs in storage


• 
  LIST – to display the current program in memory


• 
  NEW – to name and begin writing a program in memory


• 
  OLD – to copy a previously named program from storage to memory


• 
  RENAME – to change the name of the program in memory


• 
  RUN – to execute the current program in memory


• 
  SAVE – to copy the current program from memory to storage


• 
  SCRATCH – to clear the content of the current program from memory


• 
  UNSAVE – to remove the current program from storage

These commands were often believed to be part of the BASIC language by users, but in fact they were part of the time sharing system and were also used when preparing ALGOL^[9] or FORTRAN programs via the DTSS terminals.

Usage

By the 1967–68 school year, DTSS had a library of about 500 programs including, Kemeny and Kurtz reported, "many games". In addition to 2,600 Dartmouth users, 5,550 people at ten universities and 23 high schools accessed DTSS.^[6] By the early 1970s the campus had more than 150 terminals in 25 buildings. The off-campus Dartmouth Educational Time-Sharing Network included users with 79 terminals at 30 high schools and 20 universities, including Middlebury College, Phillips Andover, Mount Holyoke College, Goddard College, The U.S. Merchant Marine Academy, Bates College, the Dartmouth Club of New York, and a Dartmouth affiliate in Jersey City, New Jersey, sharing DTSS with Dartmouth people.^[7] Because BASIC did not change, the system remained compatible with older applications; Kemeny reported in 1974 that programs he had written in 1964 would still run.^[9] The system allowed email-type messages to be passed between users and real-time chat via a precursor to the Unix talk program.

DTSS today

In 2000, a project to recreate the DTSS system on a simulator was undertaken and as a result DTSS is now available for Microsoft Windows systems and for the Apple Macintosh computer.^[10]

See also

• Timeline of operating systems


• Time-sharing system evolution

References