RISC OS is a light, open-source operating system for ARM based computers, it has been around since the 1980s. It pre-dates both Windows and Mac OS and includes many revolutionary features that have ultimately been used in many other operating systems.

RISC OS 5 is the latest version of the operating system and is developed by RISC OS Open Ltd. RISC OS 5 supports legacy systems (26-bit – pre-2002) such as the RiscPC and A7000 as well as newer 32-bit ARM-based hardware such as Beagleboard, Pandaboard and Raspberry Pi based machines. You can download RISC OS 5 free of charge from the RISC OS Open website.

All Legacy (26-bit) RISC OS computers such as the RiscPC, A7000 etc load the operating system from a physical ROM chip. This is not the case for 32-bit modern RISC OS systems – an example being that you can install RISC OS 5 on a Raspberry Pi by just loading it onto an SD card.

Want to get started with RISC OS? Check out our guide!


Between 1987 and 1998, RISC OS was bundled with every ARM-based computer manufactured by Acorn Computers. It was made especially popular by the Acorn Archimedes range, which was deployed in most educational institutes in the UK during the early to mid 90s.The Archimedes as well as the RiscPC was also widely deployed in TV and radio production enviroments in the UK as well as parts of Europe and even North America.

After the break-up of Acorn in 1998, development of RISC OS was forked and separately continued by several companies, including RISCOS Ltd, Pace Micro Technology and Castle Technology.

The last version of RISC OS made by Acorn Computers was 3.7. RISCOSLtd. released RISC OS 4 in 1999 after taking over the rights to the operating system alongside Castle Technology – who continued to produce the RiscPC and A7000 range of computers after the closure of Acorn.

RISC OS 5 from Castle Technology was released in 2002 with the launch of the Iyonix, the first 32-bit RISC OS computer – all previous machines were 26-bit.

RISCOS Ltd. released RISC OS 6 in 2006 but despite its name, it is actually incompatible with 32-bit RISC OS computers and would only run on older, 26-bit computers. Development of 26-bit only versions of the operating system – RISC OS 4 and 6 – have largely halted as of the year 2017.

Nowadays, RISC OS 5 is bundled with a number of ARM-based desktop computers and is constantly being developed further by RISC OS Open – who were responsible for porting RISC OS 5 to the Raspberry Pi as well as other well-known ARM-based boards. RISC OS 5 is shipped with the NOOBS Starter Pack SD card that comes with many Raspberry Pis.