Editing UNICOS (section)

==Development==
CX-OS was the original name given to what is now UNICOS. This was a prototype system which ran on a [[Cray X-MP]] in 1984 before the Cray-2 port. It was used to demonstrate the feasibility of using [[Unix]] on a supercomputer system, before Cray-2 hardware was available.

The operating system revamp was part of a larger movement inside Cray Research to modernize their corporate software: including rewriting their most important [[Fortran]] compiler (cft to cft77) in a higher-level language ([[Pascal (programming language)|Pascal]]) with more modern optimizations and vectorizations.

As a migration path for existing COS customers wishing to transition to UNICOS, a Guest Operating System (GOS) capability was introduced into COS. The only guest OS that was ever supported was UNICOS. A COS batch job would be submitted to start up UNICOS, which would then run as a subsystem under COS, using a subset of the systems CPUs, memory, and peripheral devices. The UNICOS that ran under GOS was exactly the same as when it ran stand-alone: the difference was that the [[Kernel (operating system)|kernel]] would make certain low-level hardware requests through the COS GOS hook, rather than directly to the hardware.

One of the sites that ran very early versions of UNICOS was [[Bell Labs]], where Unix pioneers including [[Dennis Ritchie]] ported parts of their [[Research Unix|Eighth Edition Unix]] (including [[STREAMS]] [[input/output]] (I/O)) to UNICOS. They also experimented with a guest facility within UNICOS, allowing the stand-alone version of the OS to host itself.