COS, Core Operating System, and DOS, Disc Operating System, were the first operating systems for the 4080.
DOS included disc support, both for filing and for overlay (4080's term for swapping). The filing system was organised in disc regions, with each region having flat namespace for files. The system supported only a single user at once, but files had the concept of ownership, access protection, and different filetypes handled by the operating system itself. The user could run multiple programs simultaneously. See the Software section of the 4080 Sales Brochure for more details of software packages available initially.
DOS gradually gave way to OS4000, and when GEC Computers eventually ceased support of DOS, it gave the source code to the User Group.
OS4000 is the main operating system for the 4000 series processors, and was introduced in around 1977. OS4000 supports multiple simultaneous users, and the DOS filing system is extended into a full catalogue (c.f. unix directory) file system. Users are restricted mainly to running only a single program each at once, although a customer modified varient (Rutherford Laboratory), of OS4000 called OS4000+Rlix removed this restriction.
OS4000 JCL was heavily based on the Cambridge University IBM 370 Phoenix command interpretor of the same period.
This release introduced support for linked operating systems, initially for University College London's Computer Centre Euclid system, based on a GEC 4085 'hub' machine holding all user files, and 3 'rim' GEC 4082's which were the compute servers.
Release 4.1 introduced support for the GEC 4090 processor, with it's 32bit PAS (Paged Address Space) addressing. This was the last release which OS4000+Rlix was ported to.
Release 4.8 introduced the multiplexed terminal driver software, TF/TC (however, it took several more releases before TF/TC became stable).
Release 4.13 introduced support for 150 user modules, to support an upgraded Euclid system at University College London (GEC 4090 'hub', and 4 'rim' GEC 4190's).
Release 5.0 replaced the CFS1 catalogue filing system with a new CFSX catalogue filing system. This met with much user objection, and Release 5.1 reintroduced the CFS1 catalogue filing system, with both running in parallel. Release 5 was originally to have supported a new filing system called CFS2, but this was ditched at the end of development.
Release 6 introduced support for running on multi-processor 4000's.
NOS, Network Operating System, was a very cut-down store resident operating system, halfway beween DOS and OS4000. It was used to support some Communications applications, mainly Type I and Type II Packet Switch Exchanges.
SCP-2 was a certified secure operating system, supporting multi-level secure working on a single machine.