This article is about the operating system distributed by Cray Research. CTSS may also stand for Compatible Time Sharing System, an unrelated operating system developed by the MIT Computer Centre.

The Cray Time Sharing System, also known in the Cray

Cray

Cray Inc. is an American supercomputer manufacturer based in Seattle, Washington. The company's predecessor, Cray Research, Inc. , was founded in 1972 by computer designer Seymour Cray. Seymour Cray went on to form the spin-off Cray Computer Corporation , in 1989, which went bankrupt in 1995,...

 user community as CTSS, was developed as an operating system

Operating system

An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

 for the Cray-1

Cray-1

The Cray-1 was a supercomputer designed, manufactured, and marketed by Cray Research. The first Cray-1 system was installed at Los Alamos National Laboratory in 1976, and it went on to become one of the best known and most successful supercomputers in history...

 or Cray X-MP line of supercomputer

Supercomputer

A supercomputer is a computer at the frontline of current processing capacity, particularly speed of calculation.Supercomputers are used for highly calculation-intensive tasks such as problems including quantum physics, weather forecasting, climate research, molecular modeling A supercomputer is a...

s. CTSS was developed by the Los Alamos Scientific Laboratory

Los Alamos National Laboratory

Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...

 (LASL now LANL) in conjunction with the Lawrence Livermore Laboratory

Lawrence Livermore National Laboratory

The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...

 (LLL now LLNL). CTSS was popular with Cray sites in the United States Department of Energy

United States Department of Energy

The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...

 (DOE).

The predecessor of CTSS was the Livermore Time Sharing System

Livermore Time Sharing System

The Livermore Time Sharing System was a supercomputer operating system originally developed by the Lawrence Livermore Laboratories for the CDC 7600 series of supercomputers....

 (LTSS) which ran on Control Data CDC 7600

CDC 7600

The CDC 7600 was the Seymour Cray-designed successor to the CDC 6600, extending Control Data's dominance of the supercomputer field into the 1970s. The 7600 ran at 36.4 MHz and had a 65 Kword primary memory using core and variable-size secondary memory...

 line of supercomputers. The first compiler was known as LRLTRAN, for Lawrence Radiation Laboratory

Lawrence Berkeley National Laboratory

The Lawrence Berkeley National Laboratory , is a U.S. Department of Energy national laboratory conducting unclassified scientific research. It is located on the grounds of the University of California, Berkeley, in the Berkeley Hills above the central campus...

 forTRAN. The Cray version, including vectorization, was known as CVC, pronounced "Civic" like the Honda car of the period, for Cray Vector Compiler.

Some controversy existed at LASL with the first attempt to develop an operating system for the Cray-1 named DEIMOS

Deimos

Deimos, a Greek word for dread, may refer to:*Deimos , one of the sons of Ares and Aphrodite in Greek mythology*Deimos , the smaller and outermost of Mars' two natural satellites*Deimos , villain for the Warlord comic series...

, a message-passing, Unix-like

Unix-like

A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....

 operating system, by Forrest Basket. DEIMOS had initial "teething" problems common to the performance of all early operating systems. This left a bad taste for Unix-like systems at the National Laboratories and with the manufacturer, Cray Research, Inc., of the hardware whom went on to develop their own batch oriented operating system, COS (Cray Operating System

Cray Operating System

The Cray Operating System was Cray Research's proprietary operating system for its Cray-1 and Cray X-MP supercomputers, and those platforms' main OS until replaced by UNICOS in the late 1980s...

) and their own vectorizing Fortran compiler named "CFT" (Cray ForTran) both written in the Cray Assembly Language (CAL).

CTSS had the misfortune to have certain constants, structures, and lacking certain networking facilities (TCP/IP) which were optimized to be Cray-1 architecture-dependent without extensive rework when larger memory supercomputers like the Cray-2 and the Cray Y-MP came into use. CTSS has its final breaths running on Cray instruction-set-compatible hardware developed by Scientific Computer Systems (SCS-40 and SCS-30) and Supertek S-1, but this did not save the software.

CTSS embodied certain unique ideas such as a market-driven priorities for working/running processes.

An attempt to succeed CTSS was started by LLNL named NLTSS (New Livermore Time Sharing System) to embody advanced concepts for operating systems to better integrate communication using a new network protocol named LINCS while also keeping the best features of CTSS. NLTSS followed the development fate of many operating systems and only briefly ran on period Cray hardware of the late 1980s.

The earliest literature references are likely to be found in proceedings of the Cray User Group (CUG) and the
ACM

Association for Computing Machinery

The Association for Computing Machinery is a learned society for computing. It was founded in 1947 as the world's first scientific and educational computing society. Its membership is more than 92,000 as of 2009...

SOSP (Symp. on Operating Systems Proceedings). However, owning to the fact that LANL and LLNL were nuclear weapons facilities, some aspects of security are likely to doom finding out greater detail of many of these pieces of software.