RISC OS FAQ

Frequently asked questions

What is RISC OS?

RISC OS (Reduced Instrcution Set Computer Operating System) is an OS for desktop computers running ARM processors. RISC OS was originally developed by Acorn Computers Ltd in Cambridge, England has been in continual development since 1989.

What computers can run RISC OS?

Whilst RISC OS is designed for use on ARM processors modern emulation means that RISC OS can be run on both Windows and MacOS X computers. Products such as VirtualAcorn can run RISC OS (and RISC OS apps) many times quicker than any real RISC OS based hardware. There are also a number of free emulators such as RPC-Emu that can run various different versions of RISC OS on a number of platforms.

Stuff apps, what about games?

RISC OS, being a primarily British operating system, has a large number of unique games. These fall into 2 main categories. Games designed for first generation machines such as the Archimedes, A3000, A4000 and A5000 are the most common. The best version of RISC to use for first generation games is RISC OS 3.10. More advanced games with 3D graphics tend to designed for second generation RiscPC computers. Some of these games were never updated for StrongARM processors so the best version of RISC OS for these games is RISC OS 3.60.

What's the RISC OS story then?
(a 'not as short as it was supposed to be' short story of RISC OS).

Today ARM processor designs are everywhere, in phones, tablets, MP3 players, TVs, fridges, toasters and many other places. No doubt you will have several ARM designed processors in your home. However it wasn't always so. In 1987 Acorn Computers Ltd released a ground brakeing desktop computer, the Archimedes. This was the first desktop computer with a RISC (Reduced Instruction Set) processor. At the time its 4Mhz ARM 2 processor made it the most powerful desktop computer you could buy. Acorn were already well known for the BBC Micro, which used a standard 8 bit 6502 processor. By 1985 the BBC Micro was looking old fashioned, the world was moving toward 16bit computers such as the Commodore Amiga or Apple Mac.

Acorn decided to skip an entire generation and move to a 32bit processor and to design the processor in-house using the latest in computer research. The original ARM 1 (Acorn RISC Machine) processor was built and tested as a second processor connected to the BBC Micro hardware. The ARM 2 and it's supporting VIDC video and MEMC memory controller were all designed by Acorn themselves. As well as working on a ground braking computer Acorn were also working on a completely new operating system for their new RISC based computer. That operating system was RISC OS.

By 1987 the Archimides hardware ready, but RISC OS had not been completed. Acorn could not wait so the first Archimedes machines shipped with a simplified operating system, called Arthur, based on the completed parts of RISC OS. Arthur had to be assembled quickly, but the power of the ARM 2 chip made the job easier. The Arthur 'desktop' wasn't written in Assembler or C, instead it was written in 32bit BBC BASIC.

It took 2 more years before RISC OS was completed. RISC OS 2 was finally released in April 1989 and immediately won rave reviews. It was a huge step up from Arthur as it provided a 'proper' desktop that could run multiple apps with effective multi-tasking. Writing applications for RISC OS was easy, even BBC BASIC code ran at speeds undreamed of a few years earlier. By today's standards RISC OS 2 is primative but Acorn continued to develop RISC OS and improve it.

By 1991 Acorn were ready to release the next version of RISC OS and the next version of ARM processor. The new Acorn A5000 was at least 5 times as powerful as the Archimedes. Acorn included many new features in RISC OS 3.00 which were inspired by the huge range of RISC OS 2 'add-ons' available from thriving 'freeware' scene. RISC OS 3.00 was initially well received but soon problems surfaced. Acorn could build brilliant hardware, but needed a couple of attempts to build brilliant software. RISC OS 3.10 was released within a few months and became the final official release of RISC OS for the first generation of ARM 2/ARM 3 machines.

Acorn continued to develop RISC OS and build new desktop computers for most of the 1990's. The design of the ARM chips was spun out into another company, ARM Ltd. The name ARM (Acorn RISC Machine) was soon changed to Advanced RISC Machine. In 1994 Acorn released the RiscPC with RISC OS 3.50. The RiscPC was a good machine, but by this time the competition was closing and Acorn no longer made the world's fastest desktop computers. Acorn continued to develop RISC OS, RISC OS 3.60 added support for the ARM710 processor. RISC OS 3.7 was the first version of RISC OS to support a processor not designed by ARM. That processor was the DEC StrongARM. The StrongARM provided a huge performance boost for RISC OS. BBC BASIC in particular could perform up to 10 times quicker. The StrongARM and RISC OS 3.70 reclaimed some of the lost ground but Acorn were struggling.

By 1998 Acorn were working on RISC OS 3.8 and on the 'Phoebe' RiscPC replacement. However a falling market share and unspectacular revenues had made Acorn weak. When ARM Ltd had been created Acorn had kept a large number of the new company's shares. As shares in ARM Ltd had gained value the shares in Acorn had lost value. Acorn then found itself in the perilous position where the total value of the ARM shares Acorn owned was more than the total value of Acorn's own shares. The financial vultures were circling.

Acorn staff were still developing RISC OS on the day the company collapsed. The new 'owners' asset stripped the company and another great British brand was no more. The ARM shares were sold for a profit. Pace Microtechnology Ltd purchased the engineers and took over the physical property. Castle Technology Ltd took over the sales and manufacture of the Acorn computers. What about RISC OS? A new company called RISCOS Ltd was set up by a commitee of Acorn dealers and developers with the aim of taking over development of RISC OS. RISC OS 3.8 was finished and bug fixed and was released as RISC OS 4.02 in July 1999.

At this stage there were several companies interested in making RISC OS compatible hardware. Castle Technology was already selling RiscPC and A7000+ machines and wanted to include RISC OS 4 ROMs as standard. Both MicroDigital and RiscStation were working on machines based on the ARM 7500 processor. All 3 of them wanted RISC OS, but none of them wanted the others to include a higher numbered version of RISC OS. This led to the release of 3 different versions of RISC OS 4.03, all very slightly different and designed for each customer. If you ever come across a set of RISC OS 4.03 ROMS for a RiscPC then these are Castle Technology versions as MicroDigital and RiscStation used a different motherboard design.

One other version of RISC OS 4 was released, this was for the Castle Kinetic RiscPC. This used a standard RiscPC motherboard but with a specially designed processor card which included the machine's main RAM as well as the CPU. This helped resolve one of the bottlenecks with the RiscPC, slow memory access. In some tests the Kinetic running at 300 MHz was more than 10 times the spped of a 200 Mhz StrongARM. However in the real world the expensive Kinetic didn't provide much extra performance. Cheaper overclocked Revision T StrongARM chips running at 287 Mhz provided nearly the same performance at one third the cost.

Once RISC OS 4 had been completed RISCOS Ltd started looking at what other work could be done to RISC OS. Instead of working to the current RISC OS Model of releasing a new set of physical ROM chips every 1 to 2 years a new subscription model was developed. New development versions of RISC OS would be released several times a year. The customer would subscribe on a yearly basis and receive a years worth of new releases. The new scheme used soft loaded ROM images and was called RISC OS 'Select'.

By the third year of RISC OS Select it was decided to attempt to fit a Select ROM image (6MB) into a pair of physical ROM chips (4MB). Increadably this feat was acheived and RISC OS 4.39 was released both as a Select softload and as an 'Adjust' physical ROM. The names 'Select' and 'Adjust' came from the names of the RISC OS mouse buttons, Select on the left and Adjust on the right (with Menu in the middle).

Traditionally RISC OS has run on 32bit ARM processors using the special '26 bit' mode that Acorn had designed for the purpose. However Acorn were gone and whilst a number of ARM chips did include the 26bit mode it wasn't tested and there was no guarantee that 26bit mode would work on any specific processor. The solution was to re-write RISC OS to run in 32bit mode. The trade off was that any applications compiled with current 26 bit compilers would fail. With it's hardware partner Advantage Six RISCOS Ltd developed RISC OS 4.4x, which was a 32 bit version of RISC OS 4.39 with support for abstracted hardware. RISC OS 4.4x was supplied with the A9 mini computer, apart from being 32 bit and supporting the A9 hardware this version of RISC OS is nearly identical to RISC OS 4.39.

The ex-Acorn engineers who had been working at Pace hadn't given up faith with RISC OS and were still working on it. RISCOS Ltd had passed over the source code to RISC OS 4.02 and this was converted to 32bit as a black book project and was given the name RISC OS 5.

After the release of RISC OS 4.39 RISCOS Ltd didn't release another version of RISC OS for some 3 years. A new team was assembled to re-organise RISCOS Ltd's development projects. The result was RISC OS Six. The first version of RISC OS Six, in 2007, was a preview edition with some features disabled (for example printing). The preview was designed to softload on top of either RISC OS 4.02 or 4.39 and was made freely available. Further versions of RISC OS Six were released as part of a re-launched 'Select' scheme. The final version being RISC OS 6.20 in December 2009.

Over the previous decade the companies making RISC OS hardware had disapeared. Firstly RiscStation, then MicroDigital and finally Castle Technology all ceased trading. However none of these were RISCOS Ltd's biggest buyer of RISC OS licences. The biggest buyer was 3QD Developments Ltd, who used RISC OS licences in it's VirtualAcorn products. As such it made sense for 3QD Developments Ltd to take over RISC OS sales/developments in April 2012 when RISCOS Ltd closed down.

That's the brief story of RISC OS, it's not complete, not everyone gets a namecheck but it's all true.

© Copyright 3QD Developments - 28/10/2015