Arthur

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Arthur is an early operating system (OS) that was used on Acorn ARM-cpu-based computers from about 1987 until the much-superior version called RISC OS 2 was completed and made available in April 1989. It was the operating system of the earliest Archimedes ARM machines.

It was bundled with a primitive desktop graphical user interface (GUI). It features a colour-scheme typically described as "technicolour". Its earlier revisions were very buggy, and was superseded by RISC OS 2 (a name chosen instead of Arthur 2) which was developed from it.

The graphical desktop runs on top of a command-line driven operating system which owe much to Acorn's earlier MOS operating system for its BBC Micro range of 8-bit microcomputers.

Name

The "Arthur" name was supposedly dropped from version 2 because of the release at the time of a movie called Arthur 2: On the Rocks. Arthur is said to stand for "A Risc-based operating system by THURsday". (Paul Fellows who lead the project says "it stood for ARM-on-Thursday" reflecting the time-scale that we were given to develop it in)

The Arthur project team,led by Paul Fellows, was given just five months to develop it entirely from the ground up - with the directive "just make it like the BBC micro". It was intended as a stop-gap until the revolutionary operating system which Acorn had under development (ARX) could be completed. However, the latter became delayed time and again, and was eventually dropped when it became apparent that the arthur development could be extended to have a window manager and full desktop environment. Also it was small enough to run on the first 512K machines with only a floppy disc, whereas ARX required 4 megabytes and a hard drive.

The first reliable release was version 1.2 - echoing the history of the early BBC micro OS which also had 1.2 as its "standard" release.

RISC OS

No other versions were then released externally, but internally the development of the desktop and window management continued, with the addition of a cooperative multi-tasking system, invented by Neil Raine, which cleverly used the memory management hardware to swap-out one task, and bring in another between call-and-return from the WIMP-Poll call that applications were obliged to make to get messages under the desktop. This transformed it from a single-application-at-a-time system, to one that could operate a full multi-tasking desktop. This transformation took place at version 1.6 though it was not made public until released, with the name change from Arthur to RISC OS, as version 2.0.

Compatibility

Most software made for Arthur 1.2 can be run under RISC OS 2 and later because, underneath the desktop, the original Arthur OS core, API interfaces and modular structures remain as the heart of all versions. (A few titles will not work, however, because they used undocumented features, side effects or in a few cases APIs that became deprecated).

References

External links

• Arthur Lives! - a guide by Ben Jefferys
• Arthur OS Emulator (original site has been taken down - discovered 2009/01/26)