History of RISC OS

ROL had in March 1999 licensed the rights to RISC OS from Element 14 (the renamed Acorn) and eventually from the new owner, Pace Micro Technology.

[5] 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".

However, the latter was 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.

[7] No other version of the operating system was released externally, but internally the development of the desktop and window management continued, with the addition of a cooperative multitasking system, implemented by Neil Raine, which 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.

Reminiscent of a similar technique employed by MultiFinder on the Apple Macintosh,[8] this transformed a single-application-at-a-time system into one that could operate a full multi-tasking desktop.

[11] At this stage, Computer Concepts, who had been prolific developers for the BBC Micro and who had begun software development for the Archimedes, had already initiated a rival operating system project, Impulse, to support their own applications (including the desktop publishing application that would eventually become Impression), stating that Arthur did not meet the "hundreds of requirements" involved including "true multi-tasking".

[16] It is organised as a relatively small kernel which defines a standard software interface to which extension modules are required to conform.

Much of the system's functionality is implemented in modules coded in the ROM, though these can be supplanted by more evolved versions loaded into RAM.

Among the kernel facilities are a general mechanism, named the callback handler, which allows a supervisor module to perform process multiplexing.

This facility is used by a module forming part of the standard editor program to provide a terminal emulator window for console applications.

The same approach made it possible for advanced users to implement modules giving RISC OS the ability to do pre-emptive multitasking.

[17] RISC OS 3 introduced a number of new features,[18] including multitasking Filer operations, applications and fonts in ROM, no limit on number of open windows, ability to move windows off screen, safe shutdown, the Pinboard, grouping of icon bar icons, up to 128 tasks, native ability to read MS-DOS format discs and use named hard discs.

The OS features much improved hard disk access and its networking was enhanced to include TCP/IP as standard in addition to Acorn's existing proprietary Econet system.

This required extensive code changes due to StrongARM's split data and instruction cache (Harvard architecture) and 32-bit interrupt modes.

The FE offered hardware support for floating point mathematics, which until then was usually emulated in one of the RISC OS Software modules).

[20] Acorn officially halted work in all areas except set-top boxes in January 1999 and the company was renamed Element 14[21] (the 14th element of the periodic table being silicon) with a new goal to become purely a Silicon design business (like the previous very successful spin off of ARM from Acorn in 1990).

Acorn held discussions with many interested parties, and eventually agreed to exclusively licence RISC OS to RISCOS Ltd, which was formed from a consortium of dealers, developers and end-users.

[24] Whilst the hardware support for Phoebe was not needed, the core improvements to RISC OS 3.80 could be finished and released.

[38] By providing soft-loads, physical ROM costs are eliminated and updates are able to be delivered with accelerated speed and frequency.

[39] It has also allowed the company to subsidise the retail price of ROM releases, which are generally a culmination of the last few Select upgrades with a few extra minor changes.

RISC OS Six brought portability, stability and internal structure improvements, including full 26/32-bit neutrality.

It is now highly modularised, with legacy and hardware specific features abstracted, and other code separated for easier future maintenance and development.

[citation needed] RiscStation R7500, MicroDigital Omega and Mico computers will not officially be supported, as the company does not have test machines available and requires proprietary software code to which they do not have the rights.

[52] Lack of detailed technical information about the MicroDigital Omega has also been cited as being another reason why support of that hardware is difficult.

[citation needed] In April 2009 the final release of Select 5 was shipped[47] that included:[53] The final release of RISC OS from RISCOS Ltd was Select 6i1, shipped in December 2009, it includes;[54] RISC OS 5 is a separate evolution by Castle Technology Ltd based upon work done by Pace for their NCOS based set top boxes.

RISC OS 5 was written to support Castle's Iyonix PC Acorn-compatible, which runs on the Intel XScale ARM processor.

Although a wealth of software has now been updated, a few older applications can only be run on RISC OS 5 via an emulator called Aemulor, since the ARMv5 XScale processor does not support 26-bit addressing modes.

In October 2006, Castle Technology Ltd announced a plan to release elements of RISC OS 5 under a source sharing license.