The branch was initially staffed with people being released by the end of work on the OMP operating system for the Ferranti Orion.
[3] In July 1965, a team from ICT was present at a seminar at NPL describing the CTSS operating system developed for MIT's Project MAC.
In November 1965 H. P. Goodman, head of the Operating Systems Branch attended the Fall Joint Computer Conference in Las Vegas where plans for Multics were initially described.
[4] Some of the Multics features discussed influenced future development of George, notably the tree structured filestore.
Towards the end of 1965, ICT marketing requested that a simpler operating system be made available quickly, especially for the smaller members of the range.
George 3 was implemented as a small memory-resident part and a collection of chapters (overlays) which were loaded into and removed from memory as needed.
User-level code was run using preemptive multitasking; context switches were forced on I/O operations or clock ticks.
If an attempt was made to access a currently off line file the job would be suspended and the operators requested to load the appropriate tape.
The underlying disc storage mechanism George 3, in 1968, was probably the earliest commercial version of a Copy-On-Write file system.
If the machine failed at any point, it was guaranteed by the hardware that the file would be in either its original, unmodified, form or fully up to date.
Another useful feature was that the Filestore could emulate all the standard peripherals, such as card readers and punches, magnetic tapes and discs.
For the last released version, 8.67, most of the patches from the MEND exchange scheme were included in the standard George source, switched off by conditional compilation.
George was well documented internally in a series of looseleaf folders, distributed as an initial version plus amendments.
Eventually all the original pages were replaced, so any new copy of the manuals consisted of a box of empty looseleaf folders and a pile of amendments.
A modified version of George 3 was supplied to the University of Manchester Regional Computer Centre (UMRCC).
[citation needed] With the release of ICL's "new range", the 2900 series with its VME operating system, George became obsolete.
[10] David Holdsworth and Delwyn Holroyd obtained copies of George 3 issue tapes when the last live site in the UK, at British Steel Corporation, was being decommissioned and wrote an emulator for the 1900 hardware and executive that allows running of George on Microsoft Windows and Linux as part of a project for the Computer Conservation Society.