RISC OS

RISC OS

Developer	Acorn Computers (Arthur 1.x-3.7), RISCOS Ltd (4.02-6.20), RISC OS Open Ltd (5.x)
Source model	Closed source (1.20-6.x), Open source (5.x)
Initial release	Arthur 1.20 (July 1987)
Latest release	RISC OS 6.20 (December 2009)
Latest preview	RISC OS 5.31 (Nightly)
Supported platforms	ARM
License	Proprietary (RISC OS 6.x), Apache License 2.0 (RISC OS Open 5.26 onwards)

RISC OS is an operating system developed by Acorn Computers, initially released as Arthur for their Archimedes line of machines, and later on, their RiscPC line as well. After Acorn broke up in 1998, the code of the operating system was forked and being maintained by different companies, such as RISCOS Ltd, Pace Micro Technology and Castle Technology.

In July 1999, RISCOS Ltd released RISC OS 4, based on the code for RISC OS 3.80, and it includes various improvements into the operating system, such as long file name support, a new file system and more.

In May 2001, the company introduced the RISC OS Select scheme, a subscription based service that allows users to get OS updates from the RISC OS Select's website or via CDs.

In June 2004, the company released RISC OS Adjust (version 4.39, Select 3i4), introducing user customization, and became the baseline version.

Further Select releases were under the RISC OS Six banner, as the first preview of Select 4 was released to subscribers for free on 2006. RISC OS Six introduced a lot of improvements and changes to the operating system such as a new installer UI, improved stability, overall update for documentation, and more.

The final Select release (6i1) was released on December 2009, with improvements for configurations as well as Paint and Task Manager, among others.

In 2002, Castle Technology released RISC OS 5.x for their Acorn clone, the Iyonix PC, which ran on an Intel XScale ARM processor. Although most software were updated, a few can only run on an emulator called Aemulor, since the processor can't support 26 bit addressing modes.

In 2006, Castle Technology announced a shared source license with RISC OS Open Ltd. (ROOL) for RISC OS 5. In 2018, RISC OS Developments acquired the rights of RISC OS 5 and relicensed it under Apache 2.0.

Currently, it was being maintained by RISCOS Ltd. and the RISC OS Open community. It can be currently run on OMAP3 BeagleBoard, Raspberry Pi, A7000/A7000+, RiscPC, OMAP4 PandaBoard, Titanium and the Iyonix, with an upcoming port for the WandBoard and OMAP5.

Version list

Arthur

• Arthur 0.20
• Arthur 0.30
• Arthur 1.0
• Arthur 1.1
• Arthur 1.2

RISC OS 2

• RISC OS 2.00
• RISC OS 2.01
• RISC OS 2.50

RISC OS 3

• RISC OS 3.00
• RISC OS 3.10
• RISC OS 3.11
• RISC OS 3.12
• RISC OS 3.19
• RISC OS 3.21
• RISC OS 3.50
• RISC OS 3.60
• RISC OS 3.70
• RISC OS 3.71
• RISC OS 3.80 Beta

RISC OS 4

• RISC OS 4.00
• RISC OS 4.01
• RISC OS 4.02
• RISC OS 4.03
• RISC OS 4.04
• RISC OS 4.10
• RISC OS 4.11
• RISC OS 4.20

RISC OS 4 (Select/Adjust)

• RISC OS 4.23
• RISC OS 4.24 (Select 1i1)
• RISC OS 4.27 (Select 1i3)
• RISC OS 4.28 (Select 1i5)
• RISC OS 4.29 (Select 1i9)
• RISC OS 4.32 (Select 2i1)
• RISC OS 4.33 (Select 2i3)
• RISC OS 4.36 (Select 3i1)
• RISC OS 4.37 (Select 3i2)
• RISC OS 4.37 (Select 3i3)
• RISC OS 4.39 (Select 3i4)
• RISC OS 4.39 (Adjust)

RISC OS 5 (Castle)

• RISC OS 5.00
• RISC OS 5.02
• RISC OS 5.05

RISC OS 5 (ROOL)

Note: All stable builds are in even numbers.

• RISC OS 5.14
• RISC OS 5.15
• RISC OS 5.16
• RISC OS 5.17
• RISC OS 5.18
• RISC OS 5.19
• RISC OS 5.20
• RISC OS 5.21
• RISC OS 5.22
• RISC OS 5.23
• RISC OS 5.24
• RISC OS 5.25
• RISC OS 5.26
• RISC OS 5.27
• RISC OS 5.28
• RISC OS 5.29
• RISC OS 5.30

RISC OS 6 (Select 4-6)

• RISC OS 6.02 (Select 4i1)
• RISC OS 6.06 (Select 4i2)
• RISC OS 6.06 (Select 4i3)
• RISC OS 6.10 (Select 4i4)
• RISC OS 6.14 (Select 5i1)
• RISC OS 6.16 (Select 5i2)
• RISC OS 6.20 (Select 6i1)