top of page

RISC Operating System

RISC OS is a computer operating system originally designed by Acorn Computers Ltd in Cambridge, England. First released in 1987, it was designed to run on the ARM chipset, which Acorn had designed concurrently for use in its new line of Archimedes personal computers. RISC OS takes its name from the reduced instruction set computer (RISC) architecture it supports.


RISC OS was originally released in 1987 as Arthur 1.20. The next version, Arthur 2, became RISC OS 2 and was released in April 1989. RISC OS 3.00 was released with the A5000 in 1991, and contained many new features. By 1996, RISC OS had been shipped on over 500,000 systems.

Acorn officially halted work on the OS in January 1999, renaming themselves Element 14. In March 1999 a new company, RISCOS Ltd, licensed the rights to develop a desktop version of RISC OS from Element 14, and continued the development of RISC OS 3.8, releasing it as RISC OS 4 in July 1999. Meanwhile, Element 14 had also kept a copy of RISC OS 3.8 in house, which they developed into NCOS for use in set-top boxes. In 2000, Element 14 sold RISC OS to Pace Micro Technology, who later sold it to Castle Technology Ltd.

In May 2001, RISCOS Ltd launched RISC OS Select, a subscription scheme allowing users access to the latest RISC OS 4 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. Select 1 was shipped in May 2002, with Select 2 following in November 2002 and the final release of Select 3 in June 2004. In the same month, RISC OS 4.39, dubbed RISC OS Adjust, was released. RISC OS Adjust was a culmination of all the Select Scheme updates to date, released as a physical set of replaceable ROMs for the RiscPC and A7000 series of machines.

Meanwhile, in October 2002, Castle Technology released the Acorn clone Iyonix PC. This ran a 32-bit (in contrast to 26-bit) variant of RISC OS, named RISC OS 5. RISC OS 5 is a separate evolution of RISC OS based upon the NCOS work done by Pace. The following year, Castle Technology bought RISC OS from Pace for an undisclosed sum. In October 2006, Castle announced a shared source license plan, managed by RISC OS Open Limited, for elements of RISC OS 5.

In October 2018, RISC OS 5 was re-licensed under the Apache 2.0 license.

In December 2020, the source code of RISC OS 3.71 was leaked to The Pirate Bay


  1. RISC OS is quite fast.

  2. Almost Universal drag and drop for file save, file load, copy/cut/paste and much more.

  3. Very consistant User interface.

  4. Very easy to learn even for a new user.

  5. A structured BASIC inturpreter is standard in the OS

  6. The ability to Single task.

  7. RISC OS has a very clean implementation of the BSD Sockets library.

  8. RISC OS is very easy to extend by writing modules.

  9. Preemptive multitasking is possible for apps that are written for it, thanks to extension modules.

  10. The WIMP (RISC OSes GUI) is very easy to program for.

  11. The API is extremely simple, to the point that if a person so wished they could learn it in its entirety.

  12. On the RPi there are at least two modules available to simplify access to the GPIO pins, and PWM


  1. USB support is still a bit buggy (Temporary Con).

  2. 802.11* support is not present at all, and looks like it will be a while before we get it.

  3. The screen driver on the RPi does not yet support HW acceleration.

  4. For users that are accustomed to the oddities of other OSes it can take a few minutes to get used to.

  5. There is not yet any way to have system wide Preemptive Multitasking.

  6. There is not yet a good clean way to do multithreading. Though there are programmers working on fixing this.

  7. The sound system can be a bit difficult to work with, when programming.

The Tech Platform

bottom of page