DTSS is an operating system for the GE 635, Honeywell 6600, and DPS8 series of 36-bit mainframes. The system was originally developed at Dartmouth in the latter 1960s, and substantially modified through the 1970s. In the early 1980s the kernel ("Executive") was rewritten to take advantage of the Honeywell VM architecture.
DTSS was much influenced by Multics, developed at the same time on similar hardware (in fact, General Moters once ran DTSS on their Multics system). DTSS, however, remained a much simpler system, running on stock hardware, with a conventional file system and large amounts of assembly language in the OS. DTSS is also related to GE's large-scale time-sharing project, GEISCO, which may now be GENIE.
DTSS time-shared processes ("jobs") in protected address spaces controlled by a base-limit register. Inter-process communication in DTSS was through "communications files", via the usual file I/O calls. These allegedly contributed to the design of pipes in UNIX. DTSS I/O calls are asynchronous, and a number of system programs exploit this with multithreaded execution. The command interpreters ("Monitors"), for example, were shared among users. This enabled the GE635 to run over 200 users in a ~1 MIPS CPU.
System calls were made by executing the MME (Master Mode Entry) instruction.
In its first versions, DTSS had only 6 (asynchronous) MMEs:
OPEN, CLOSE, SAVE, UNSAVE, COPY (which does file-file as well
as read and write transfers),
and EXECUTE.
These were in adition to a small number of synchronous MMEs to read system
date/time, process data, etc.
In typical mainframe fashion, users connected their terminals through a communications front-end minicomputer - originally a Datanet 30, later a Honeywell 716 (cousin to the Pr1me line), later still a Honeywell Level 6/DPS6 or a New England Digital Able.
DTSS (aka DCTS) was used some dozen commercial time-sharing vendors and corporate installations, as well as at educational institutions.
DTSS supported a number of programming languages
in addition to BASIC (which was always compiled, rather than interpreted).
Traces of its command interpreter ("Monitor") are found in the commands of
numerous BASIC systems, with NEW, OLD, LIST, and SAVE
commands.
With the passing of the Age of Mainframes, DTSS development has largely ceased, and its use is being phased out.
(The following synopsis is taken from the EXPLAIN HISTORY command on DCTS.) There is also a timeline.
The first computer at Dartmouth College was an LGP-30 acquired in1959. It could accommodate only one user at a time and was small and slow. The enthusiasm with which it was received, however, revealed astrong demand for a better mouse trap.
In September, 1963, under the direction of mathematics professors John G. Kemeny and Thomas E. Kurtz, a project to establish a time-sharing system at Dartmouth got under way. The fruits of this project were BASIC, a simplified programming language, and a time-sharing system -- using the GE-235 and Datanet-30 computers. This system began operations in May, 1964. In 1965, Dartmouth placed off-campus terminals in secondary schools in the area. At the same time, other computer installations began to use Dartmouth's system software.
A larger building was soon necessary. By 1966, the Kiewit Computation Center building -- a gift of Peter and Evelyn Kiewit -- housed a GE-635 system. A new operating system -- which later became known as the Dartmouth Time-Sharing System (DTSS) -- was written in 1966-1968 for the GE-635 system.
Ten years later, in January, 1976, a Honeywell 66/40 replaced the GE-635. The 66/40 was upgraded, made approximately twice as fast, in September 1978. It is now referred to as a 66/DPS-3. In 1978, the operating system was renamed Dartmouth College Time Sharing (DCTS) when the rights to the abbreviation DTSS were sold to the Metropolitan Life Insurance Company.
In 1982, we acquired a Honeywell DPS 8/44 computer to run a second DCTS system. This and other computers, which have been added since 1979, are connected through special communications cabling and machinery known as the Kiewit Network. The other computers currently on the network include a Prime 750 which runs the PRIMOS operating system, two Vax 11/750s running UNIX (a trademark of Bell Laboratories), and a Vax 11/780 running the VMS operating system. The College's library catalogs are being placed on-line using one of the Vax 11/750s.