RISC OS

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This article is about the operating system created by Acorn Computers. For the MIPS Magnum operating system, see RISC/os.

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RISC OS, which stands for Reduced Instruction Set Computing Operating System is a British Graphical user interface-based operating system for ARM-processor based computers or similar devices. In certain countries (particularly the UK) it was an important operating system before the dot-com computing era.

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Bundled Applications

Applications bundled with RISC OS varied slightly with each version, but usually included the following core apps:

  •  !Paint - a basic bitmap-based drawing program.
  •  !Draw - a surprisingly sophisticated vector-based drawing program.
  •  !Calc - a basic calculator application.
  •  !Edit - a text editor.

Applications were contained in a folder, which, if it's first character was '!' (pling) would be treated as an application, with an icon, and executable files etc contained within the folder, but transparent to the user.

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Early years (Arthur)

Template:Main Image:AcornArthur110desktopsmall.pngThe OS was designed in England by Acorn for the 32-bit ARM based Acorn Archimedes, and released in its first version in 1987, as the Arthur operating system.

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RISC OS 2

RISC OS was a rapid development of Arthur 1.2 after the failure of the ARX project. The first release was to be called Arthur 2, but was renamed to RISC OS 2, and was first sold as RISC OS 2.00 in April 1989. It had co-operative multitasking with some limitations, but was not multithreaded. It used the ADFS filesystem for both floppy and hard discs. It initially ran from a 512 KB ROM module. The WIMP interface offered all the standard features and fixed many of the bugs that had hindered Arthur. It lacked virtual memory and extensive memory protection (applications are protected from each other, but many functions have to be implemented as 'modules' which have full access to the memory). The main advantage of the OS was its ROM; it booted very quickly and while it was easy to crash it was impossible to break. Its high performance was due to much of system being written in ARM assembly language. The OS was organised as a relatively small kernel which defined a standard software interface to which extension modules were required to conform. Much of the system's functionality was implemented in modules coded in the ROM, though these could be supplanted by more evolved versions loaded into RAM. Among the kernel facilities were a general mechanism, named the callback handler, which allowed a supervisor module to perform process multiplexing. This facility was 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.

One unusual and innovative feature of the operating system at the time of its release was its support for high-quality, hinted and anti-aliased outline font rendering, a feature that only became widespread in other operating systems much later.

A slightly updated version RISC OS 2.01 was released later to support the ARM3 processor that was shipped with the Archimedes A540 and Acorn R225/R260.

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RISC OS 3

Image:RiscOSArtworksTechWriter.png RISC OS 3.00 was released with the A5000 in 1991; it was almost four times the size of RISC OS 2 and ran from a 2MB ROM. It improved multitasking and also placed some of the more popular base applications in the ROM.

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RISC OS 3.1

RISC OS 3.1, was released later which was sold built-in to the A3010, A3020, A4000, A4 and later A5000 models. It was also made available as replacement ROMs for the A5000 and earlier Archimedes machines, this is the last version suitable for those machines. Three variants were released RISC OS 3.10 the base version, RISC OS 3.11 a slight update that fixed some serial port issues, and RISC OS 3.19 which was a German translation.

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RISC OS 3.5

RISC OS 3.50 was sold from 1994 with the first Risc PCs. Due to the very different hardware architecure of the Risc PC, including an ARM 6 processor, 16 and 24bit colour and a different IO chip (IOMD), RISC OS 3.50 was not made available for the older Archimedes and A Series ARM 2 and 3 machines.

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RISC OS 3.6

RISC OS 3.60 followed in 1995, the OS was updated and featured much better hard disk access and its networking was enhanced to include TCP/IP as standard in addition to Acorn's existing proprietary Econet system. Also the hardware support was improved, Risc PCs could now use ARM 7 processors and Acorn's A7000 machine with its ARM 7500 processor was also supported.

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RISC OS 3.7

RISC OS 3.70 followed in 1996, the primary changes in the OS for this version was supporting 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 (Harvard architecture).

RISC OS 3.71 is a small update released to support the hardware in the Acorn A7000+ with its ARM 7500FE processor.

RISC OS provides a very intuitive graphical user interface, with features such as context sensitive menus and pervasive drag and drop, and excellent consistency across applications thanks to Acorn's detailed Style Guide.

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Demise of Acorn Computers Ltd

Acorn halted work in all areas except Set-top boxes in late 1998, and the company was renamed to Element 14 (the 14th element of the periodic table being silicon). RISC OS development was halted during the development of OS 4.0 for the, also in development, RISC PC II ("Phoebe"), a beta version, OS 3.8 for the original RISC PC, had been released to developers.

This led to a number of rescue efforts, including the creation of the ROX Desktop to provide a RISC OS-like interface on Unix and Linux systems. Two similar projects, Impulse and Eidos's Phoenix, have both stalled.

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RISC OS 4 (RISCOS Ltd)

In 1999 a new company called RISCOS Limited was founded. They licensed the rights to RISC OS from Element 14 (and eventually from the new owner, Pace Micro) and continued the development of OS 3.8, releasing it as RISC OS 4 in July 1999. RISCOS Ltd's current version is RISC OS Select Edition 3 (RISC OS 4.39), with the ROM based version being dubbed RISC OS Adjust. According to the company, several thousand copies have been sold.

In 2004, RISCOS Limited began work on a 32-bit version of RISC OS Adjust, which would be compatible with the latest ARM processors. When released, the OS will be available in both embedded and desktop form. The first machine to make use of the updated OS, the Advantage6 A9 (Photo of Portable Desktop Version), is expected to be released in mid 2006. Matt Edgar of Advantage6 is (in)famous for saying, "When it's ready!"

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RISC OS 5 (Castle Technology)

RISC OS 5 is a separate evolution by Castle Technology Ltd based upon work done by Pace Micro Technology 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, since a minor 26-bit ARM CPU function was removed by Intel from the XScale. Likewise, RISC OS 5 itself had to be ported to run properly on the new CPU, and abstraction of the graphics and other hardware interfaces created, to allow it, for example, to use standard graphics cards, instead of Acorn's own VIDC chip.

In July 2003, Castle Technology Ltd bought the head licence for RISC OS from Pace Micro [1]. RISCOS Ltd and Castle continued maintaining separate development branches of the RISC OS operating system for some time, but as a result of a lengthy dispute over licensing during 2004 the two have agreed to merge the two competing streams.

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See also

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External links

fr:RISC OS nl:RISC OS pl:RISC OS

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