GEORGE (operating system)

George 3 was a mixed batch and online system. Jobs could be run from cards or tape in the same manner as George 2, or interactively from MOP (Multiple Online Processing) terminals, either simple Teletype Model 33 ASR terminals or block mode VDU terminals.

The job control language was the same on terminals or in batch jobs and included conditional operations and macro operations. In contrast to Unix systems the job control language was part of the operating system rather than being a user level shell process.

A job could only have one program loaded in to memory at a time, but one job could start other jobs to run concurrently, if system resources and site policy would permit. The system would swap user programs out of memory while they were waiting for input or output if other activities required memory to run.

George 3 provided a tree structured Filestore, inspired in part by Multics.

Every user of the system had a home directory with as many sub directories as needed under it. A users home directory could be accessed directly, for example the directory for user JOHN could be referred to as :JOHN, or by a full path, for example if JOHN was in the computer science department his home directory might be :MANAGER.USERS.COMPSCI.JOHN.

Access control lists were used for security, a user could permit or deny any user or group of users access to his files or directories.

File data storage was two-level: files could be either currently on disk, or, if the system was low on disk space they could be automatically relegated to magnetic tape. 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. When the tape was made available the file would be brought back to disk and the job resumed.

The underlying disc storage mechanism George 3, in 1968, was probably the earliest commercial version of a Copy-On-Write file system. The way this worked was that all modified blocks would be written to blocks on a "free" list. Blocks containing metadata were also treated in the same way but were, together with data blocks, physically written in an order in such a way that, when the final "master" block had been written, the file was committed. 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. This allowed older George 1 & 2 programs that required these physical devices, to be run under George 3 without modification. This could speed up jobs that required many tape or disc changes on George 1 & 2 to be automated to the extent that something that had required two operators, several tens of tape changes and five hours, now required no operators, other than for mounting two work tapes for the results, and finished in 45 minutes.

Starting with the 1904A, a paging unit was available for larger 1900 processors and George 4 was written to take advantage of it. George 4 remained compatible with George 3. It was common to alternate George 3 and 4 on the same machine and filestore, running George 3 during the day for small, interactive workloads and George 4 at night for large, memory intensive, jobs.[8]

George 4 introduced the concept of a sparse program, a program that had an addressing space larger than its allocated memory and read-only (pure) data and code regions. New versions of the consolidator (linker) and compilers were provided to use these facilities.

The source code of George 3 and 4 were the same; conditional compilation facilities of the GIN assembler were used to select which version of the system was being compiled.

As the 1900 paging feature was not emulated by the 2900 series machines used by later George installations, George 4 fell out of use before George 3.

George was distributed in a form that allowed a site to modify large parts of the system. A compilation of the system was started, then interrupted just before the end and dumped to magnetic tape. The GIN compiler allowed the compilation to be continued from this point at the user site, possibly modifying code already compiled.

Versions of George 3 before release 8 were provided in binary form. Any modifications needed to the system were made as binary patches. To simplify the process most George chapters included an empty MEND area at the end.

Starting with release 8 the source of George was distributed with the binary, both on magnetic tape and microfiche. A system of source level patches, known as MENDITS was used to modify the system and an existing chapter could be completely replaced by the new modified chapter.

The George user group set up a "MEND exchange scheme" to share interesting modifications to George. Some modifications were distributed freely, others were available for a fee. When ICL produced a new version of George they would sometimes include modifications produced by the users.

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. They can be turned on as part of the standard process of tailoring George for a site.

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. The first amendment was a list of contributors, and the technical reason for the amendment was described as "to keep everyone happy".

A modified version of George 3 was supplied to the University of Manchester Regional Computer Centre (UMRCC). This linked George 3 to a CDC Cyber machine, to which George supplied the offline I/O and Job queueing functions. Online support was supplied by both ICL and Cyber for both hardware and software. The Cyber support team worked in an office with the name "Cybermen" on the door.

With the release of ICL's "new range", the 2900 series with its VME operating system, George became obsolete. However, due to the legacy of investment in software for George, ICL released options to run 1900 series software, including George, on 2900 series machines, initially the Direct Machine Environment (DME), later the Concurrent Machine Environment (CME) which allowed simultaneous running of 1900 and 2900 code on the same system.

New versions of George 3 continued to be released for the 2900. The last version was 8.67, released in 1983.

As of 2005 at least one site in Russia was still running George 3 under DME.[9]

In November 2014 George 3 was run on a reconditioned ICL 2966 at the National Museum of Computing.[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.[11][12]