Cray Time Sharing System
| Company type | Operating system |
|---|---|
| Industry | Computer software |
| Predecessor | Livermore Time Sharing System (LTSS) |
| Founded | 1978 |
| Headquarters | Los Alamos / Livermore , United States |
Area served | United States Department of Energy Cray installations, San Diego Supercomputing Center, others |
| Owner | Los Alamos National Laboratory, Lawrence Livermore National Laboratory |
The Cray Time Sharing System (CTSS) was an operating system developed in 1978 specifically for the Cray-1 and Cray X-MP supercomputers. This system was created through a collaboration between the Los Alamos National Laboratory (LASL) and Lawrence Livermore National Laboratory (LLNL). CTSS gained significant adoption across various United States Department of Energy (DOE) Cray installations as well as other institutions like the San Diego Supercomputing Center.
Overview
CTSS originated as an advancement of the Livermore Time Sharing System (LTSS), which operated on Control Data CDC 7600 supercomputers. Its first compiler, known as LRLTRAN, was based on a FORTRAN 66 variant enhanced with dynamic memory capabilities. The Cray-specific compiler, CVC (Cray Vector Compiler), was developed to automatically vectorize code to boost computational efficiency.
Prior to CTSS, there were initial projects such as DEIMOS, a Unix-inspired operating system created for the Cray-1 by Forrest Basket; however, it encountered significant operational difficulties early on. Consequently, Cray Research proceeded to build their own batch processing OS, COS (Cray Operating System), along with a vectorizing Fortran compiler named CFT (Cray ForTran), both implemented in Cray Assembly Language.
Designed with tight integration to the Cray-1 hardware, CTSS’s architecture-dependent constants and absence of modern networking protocols like TCP/IP limited its adaptability to newer models such as the Cray-2 and Y-MP. Efforts to prolong its usability included running CTSS on Cray-compatible machines from Scientific Computer Systems and Supertek, but these initiatives failed to maintain its market relevance.
One of CTSS’s distinctive innovations was the implementation of market-driven scheduling priorities for processes. Later, LLNL developed NLTSS (New Livermore Time Sharing System) to incorporate advanced networking technologies such as LINCS while preserving CTSS’s core advantages; nevertheless, NLTSS had limited adoption on late-1980s Cray platforms.
Additional technical information about CTSS can be found in internal documentation and presentations from the Cray User Group and ACM SOSP conferences. Due to the classified nature of operations at LANL and LLNL, publicly available comprehensive details remain scarce.