History of RISC OS
RISC OS, the computer operating system developed by Acorn Computers for their ARM-based Acorn Archimedes range, was originally released in 1987 as ', and soon followed by ', and '. The next version, ', became ' and was completed in September 1988 and made available in April 1989. ' was released with the very earliest version of the A5000 in 1991 and contained a series of new features. By 1996 RISC OS had been shipped on over 500,000 systems.
' was released by RISCOS Ltd in July 1999, based on the continued development of. ROL had in March 1999 licensed the rights to RISC OS from Element 14 and eventually from the new owner, Pace Micro Technology. According to the company, over 6,400 copies of on ROM were sold up until production was ceased in mid-2005.
' was launched in May 2001 by ROL. This is a subscription scheme allowing users access to the latest OS updates. These upgrades are released as soft-loadable ROM images, separate to the ROM where the boot OS is stored, and are loaded at boot time. ' was shipped in May 2002, with ' following in November 2002 and the final release of ' in June 2004. ROL released the ROM based the same month, dubbed ' as a play on the RISC OS GUI convention of calling the three mouse buttons 'Select', 'Menu' and 'Adjust'. ROL sold its 500th Adjust ROM in early 2006.
' was released in October 2002 on Castle Technology's Acorn clone Iyonix PC. is a separate evolution based upon the NCOS work done by Pace for set-top boxes. In October 2006, Castle announced a source sharing license plan for elements of. This Shared Source Initiative is managed by RISC OS Open Ltd. RISC OS 5 has since been released under a fully free and open source Apache 2.0 license, while the older no longer maintained RISC OS 6 has not.
' was also announced in October 2006 by ROL. This is the next generation of their stream of the operating system. The first product to be launched under the name was the continuation of the Select scheme, '. A beta-version of, , was available in 2007 as a free download to all subscribers to the Select scheme, while in April 2009 the final release of ' was shipped. The latest release of RISC OS from ROL is , shipped in December 2009.
Arthur
The OS was designed in the United Kingdom by Acorn for the 32-bit ARM based Acorn Archimedes, and released in its first version in 1987, as the Arthur operating system.The first public release of the OS was Arthur 1.20 in June 1987.
It was bundled with a desktop graphical user interface, which mostly comprises assembly language software modules, and the Desktop module itself being written in. It features a colour-scheme typically described as "technicolor".
The graphical desktop runs on top of a command-line driven operating system which owes much to Acorn's earlier MOS operating system for its BBC Micro range of 8-bit microcomputers.
Arthur, as originally conceived, was intended to deliver similar functionality to the operating system for the BBC Master series of computers, MOS, as a reaction to the fact that a more advanced operating system research project would not be ready in time for the Archimedes.
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 operating system which Acorn had under development could be completed. 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. 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 OS development was carried out using a prototype ARM-based system connected to a BBC computer, before moving onto the prototype Acorn Archimedes the A500.
Arthur was not a multitasking operating system, but offered support for adding application-level cooperative multitasking. 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, this transformed a single-application-at-a-time system into 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.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..
In 2011, Business Insider listed Arthur as one of ten "operating systems that time forgot".
RISC OS 2
RISC OS was a rapid development of Arthur 1.2 after the failure of the ARX project. Given growing dissatisfaction with various bugs and limitations with Arthur, testing of what was then known as was apparently ongoing during 1988 with selected software houses.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, stating that Arthur did not meet the "hundreds of requirements" involved including "true multi-tasking". Such an operating system was to be offered free of charge with the planned application packages, but with the release of RISC OS and Computer Concepts acknowledging that RISC OS "overcomes the old problems with Arthur", the applications were to be able to run under either RISC OS or Impulse. Impression was eventually released as a RISC OS application.
Ultimately, was renamed to RISC OS, and was first sold as RISC OS 2.00 in April 1989.
The operating system implements co-operative multitasking with some limitations but is not multi-threaded. It uses the ADFS file system for both floppy and hard disc access. It ran from a 512 KB set of ROMs. The WIMP interface offers all the standard features and fixes many of the bugs that had hindered Arthur. It lacks virtual memory and extensive memory protection. At the time of release, the main advantage of the OS was its ROM; it booted very quickly and while it was easy to crash, it was impossible to permanently break the OS from software. Its high performance was due to much of the system being written in ARM assembly language.
The OS was designed with users in mind, rather than OS designers. 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.
A slightly updated version, RISC OS 2.01, was released later to support the ARM3 processor, larger memory capacities, and the VGA and SVGA modes provided by the Acorn Archimedes 540 and Acorn R225/R260.
RISC OS 3
introduced a number of new features, 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. Improved configuration was also included, by way of multiple windows to change the settings.RISC OS 3.00 was released with the very earliest version of the A5000 in 1991; it is almost four times the size of RISC OS 2 and runs from a 2 MB ROM. It improves multitasking and also places some of the more popular base applications in the ROM. RISC OS 3.00 had several bugs and was replaced by RISC OS 3.1 a few months later; the upgraded ROMs were supplied for the cost of postage.
RISC OS 3.1 was released later and sold built into the A3010, A3020, A4000, A4 and later A5000 models. It was also made available as replacement ROMs for the A5000 and earlier Archimedes machines. Three variants were released: RISC OS 3.10 the base version, RISC OS 3.11 which included a slight update that fixes some serial port issues and RISC OS 3.19 which was a German translation.
RISC OS 3.50 was sold from 1994 with the first Risc PCs. Due to the very different hardware architecture of the Risc PC, including an ARM 6 processor, 16- and 24-bit colour and a different IO chip, RISC OS 3.50 was not made available for the older Archimedes and A Series ARM2 and 3 machines. RISC OS 3.5 was somewhat shoehorned into the 2 MB footprint, and moved the ROM applications of RISC OS 3.1 onto the hard drive; this proved so unpopular that they were later moved back into ROM. This version introduced issues of backward compatibility, particularly with games.
RISC OS 3.60 followed in 1995. 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. The hardware support was also improved; Risc PCs could now use ARM7 processors. Acorn's A7000 machine with its ARM7500 processor was also supported. RISC OS 3.6 was twice the size of RISC OS 3.5, shipping on 4 MB in two ROM chips; components that had been moved onto disk in 3.5 were now moved back into ROM.
RISC OS 3.70 was released in 1996. The primary changes in the OS was support for the StrongARM processor that was made available as an upgrade for the Risc PC. This required extensive code changes due to StrongARM's split data and instruction cache and 32-bit interrupt modes.
RISC OS 3.71 is a small update released to support the hardware in the Acorn A7000+ with its ARM7500FE processor. The FE offered hardware support for floating point mathematics, which until then was usually emulated in one of the RISC OS Software modules).
RISC OS 3.60 also formed the foundation of NCOS, as shipped in the Acorn NetChannel NCs.