# Cray Time Sharing System

> supercomputer operating system

**Wikidata**: [Q5183024](https://www.wikidata.org/wiki/Q5183024)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Cray_Time_Sharing_System)  
**Source**: https://4ort.xyz/entity/cray-time-sharing-system

## Summary  
The Cray Time Sharing System (CTSS) is a supercomputer operating system developed for high-performance computing environments. It was designed to manage and operate Cray supercomputers, such as the Cray-1 and Cray X-MP, enabling efficient time-sharing capabilities for complex computational tasks.

## Key Facts  
- Also known as CTSS  
- Instance of: operating system, supercomputer operating system  
- Platforms: Cray-1, Cray X-MP  
- Replaced: Livermore Time Sharing System  
- Programming Language: Fortran  
- Developers: Los Alamos National Laboratory, Lawrence Livermore National Laboratory  
- Freebase ID: /m/05pqjw  
- Language of Work or Name: English  

## FAQs  
### Q: What is the Cray Time Sharing System used for?  
A: The Cray Time Sharing System (CTSS) is used to manage and operate Cray supercomputers, allowing multiple users to share system resources efficiently. It supports execution of programs written in languages like Fortran and facilitates large-scale scientific computations.

### Q: Who developed the Cray Time Sharing System?  
A: The Cray Time Sharing System was developed collaboratively by Los Alamos National Laboratory and Lawrence Livermore National Laboratory. These institutions were key contributors to early advancements in supercomputing technologies.

### Q: Which computers run the Cray Time Sharing System?  
A: CTSS runs on Cray supercomputers, specifically including models such as the Cray-1 and Cray X-MP. These machines were among the most powerful computing systems during their era.

## Why It Matters  
The Cray Time Sharing System played a pivotal role in advancing high-performance computing by providing an efficient framework for managing shared access to some of the fastest computers of its generation. As part of the broader evolution of time-sharing systems, CTSS enabled more effective utilization of expensive computational resources, supporting breakthroughs in science and engineering. Its development reflects collaborative innovation between leading U.S. national laboratories, contributing to both technological progress and strategic computing capabilities during the late 20th century.

## Notable For  
- Designed specifically for Cray supercomputers like the Cray-1 and Cray X-MP  
- Replacement for the earlier Livermore Time Sharing System  
- Enabled multi-user time-sharing functionality on high-end computing platforms  
- Utilized Fortran, a foundational language in scientific computing  
- Developed through collaboration between two major U.S. Department of Energy labs  

## Body  

### Overview  
The Cray Time Sharing System (CTSS) is a specialized operating system built for use with Cray supercomputers. It allows concurrent access by multiple users, optimizing resource usage on these high-capacity machines. CTSS evolved from previous efforts at Lawrence Livermore National Laboratory, replacing the Livermore Time Sharing System.

### Development and History  
CTSS was jointly developed by Los Alamos National Laboratory and Lawrence Livermore National Laboratory—two premier research institutions focused on national security and advanced computation. While no specific inception date is cited, its creation aligns with the deployment timeline of supported Cray systems in the late 1970s and early 1980s.

### Technical Details  
- **Platforms Supported**: Cray-1, Cray X-MP  
- **Programming Language**: Fortran – widely used in scientific applications since its introduction in 1957  
- **Functionality**: Enables multi-user time-sharing operations, improving accessibility and efficiency of supercomputing resources  

### Relationship to Other Systems  
CTSS replaced the Livermore Time Sharing System, marking an advancement in operational capability tailored for newer generations of Cray hardware. As a member of the class “supercomputer operating system,” it represents one of the few purpose-built solutions for managing vector-processing architectures typical of Cray designs.

### Legacy and Impact  
Though limited in number of site links, CTSS holds historical importance within the domain of supercomputing operating systems. It contributed to enabling broader user engagement with top-tier computational tools, laying groundwork for future developments in scalable system software design.