Unicos

UNICOS was a UNIX-based operating system developed by Cray Research for Cray supercomputers. It combined a POSIX-compliant Unix environment with Cray's high-performance kernels and interconnects to support vector processors, parallel processing, and large-scale I/O.

Introduced in the 1980s for Cray's vector and shared-memory parallel machines, UNICOS was designed to provide familiar Unix tools while exposing Cray-specific features such as optimized libraries, Cray interconnects, and supervisor-level controls for parallel workloads. It was based on UNIX System V and incorporated Cray's own extensions to support the architecture.

Cray produced variants such as UNICOS/mk for massively parallel systems, enabling distributed memory parallelism and multi-kernel execution across hundreds to thousands of processors. UNICOS environments ran on Cray models including the X/MP line, Y-MP, and later on massively parallel machines.

Over time, Cray introduced Cray Linux Environment to unify HPC workloads with Linux, and UNICOS was progressively retired on newer systems. UNICOS played a key role in enabling high-performance computing workflows by integrating Unix software ecosystems with Cray's hardware-specific optimization.