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Section 1 - Hardware and Operating Systems

 Q1.1) What is an Acorn machine?
 Q1.2) What kind of Acorn/RISC OS machines are there?
 Q1.3) What versions of the ARM processors are there?
 Q1.4) What are the differences between different RISC OS versions?
 Q1.5) What is RISC OS 3.8/Ursula?
 Q1.6) What are the graphics capabilities of RISC OS machines?
 Q1.7) Is Virtual Memory possible under RISC OS?
 Q1.8) What 'Easter Eggs' are present in RISC OS?
 Q1.9) What is the current status of Linux for Acorn machines?
 Q1.10) What is the current status of NetBSD for Acorn machines?
 Q1.11) What is 'Lazy Task Swapping'?

Q1.1) What is an Acorn machine?

Acorn computers were a British built line of computers that started with 6502 based machines and later became based upon ARM (Acorn Risc Machine) processors. Acorn computers were made by the Acorn Computer Group, originally founded in 1978 by Cambridge business men Chris Curry and Herman Hauser.

In January 1999 Acorn Computers Ltd., was renamed Element-14, focussing more on their Digital TV technology. Element-14 were later purchased by Broadcom Corporation on November 24 2000. More information can be found on their web site at

The remaining part of Acorn was later sold to Pace Micros, including the remains of their set-top box division. Thus Acorn the company, is technically no more - other than a brand name. Pace subsequently agreed to licence RISC OS, Acorn's powerful wimp-based operating system to a newly formed company called RISCOS Ltd.

Castle Technology took over the original manufacture of the Acorn Risc PC and A7000 range, and now produce the Iyonix which is currently the fastest RISC OS computer available. In 2003 Castle Technology bought the rights to RISC OS from Pace, and in 2006 a new company, RISC OS Open (ROOL) was created in order to manage the open source release of RISC OS. More details can be found on the RISC OS Open website at

Section 1.2 details those RISC OS machines currently in manufacture and how to fetch a full list of all machines known to have been made by Acorn. Acorn machines are known for their innovation, flexibility and reliability of hardware/software.

Q1.2) What kind of Acorn/RISC OS machines are there?

The full list of Acorn made machines is now getting somewhat lengthy as many variants and new machines have been launched amd discontinued in the last few years.

As of June 2002, only current machines are listed in this FAQ, as there are numerous online resources available which give details of the history of Acorn & RISC OS computers. The following sites may be useful to find out about past machines. However, I've included some information on various diverse machines (below).

What follows is an up to date list of machines currently in production and available to purchase.

The Iyonix

The Iyonix is currently the most powerful RISC OS based, ARM powered computer. Manufactured by Castle Technology, it is available in a variety of models.

It is also the only current machine running a full 32-bit version of RISC OS.

Detailed specification for the base model comprises;
Intel XScale 80321 Processor running at 600MHz.
32-bit RISC OS 5
128Mb 200MHz DDR RAM
40, 80 or 120Gb Hard Drive
UDMA 100 support
16-bit Sound system
nVidia GeForce 2MX graphics giving resolutions of up to 2048x1536 pixels in 16 million colours.
Virtually silent operation (quieter than even the latest iMac range of Apple computers)
USB Keyboard & Mouse.
USB expansion
Full PCI DMA for expansion cards

More information is available at

The A9 Home

The A9 Home is a miniature RISC OS based machine, manufactured by Advantage Six ( Based on the ARM9 processor, it's technically not quite as fast as an Iyonix, but none the less is an extremely capable machine, even more useful because its very small form factor.

Weighing in at only 6.6" x 4.1" x 2.1" in size, it has the following specification:-
Samsung ARM 9 Processor running at 400MHz
Graphics co-processor and Power control processor
8MB VRAM supporting graphics up to 16.7 million colours at resolutions of 1600x1200
40GB internal 2.5" hard disc
RISC OS Adjust32 operating system
2 x USB (1.1 standard)
2 x PS/2
3.5mm Microphone in and headphone out sockets
10/100 BaseT integral network
RS232 serial out
5V, 20W PSU, although in operation the A9 Home consumes only around 3W of power.

More information can be obtained at

Acorn RiscPC series

In 2003 Castle Technology announced that they were ceasing production of the Risc PC range, which has now been supeceded by the Iyonix PC (see above)

The Risc PC was the last generation of Acorn badged machines, superseding the original Acorn Archimedes computers. All of them were based on a highly configurable and modular system that made a bewildering variety of options available. All were founded on the 'second generation' chipset featuring VIDC20, IOMD and the latest StrongARM processor. The 'RPC' range was launched on the 15th of April 1994 with the RiscPC 600 series of machines. The last 'Kinetic' RPC was some ten times faster than the original 1994 model.

A list of older, legacy machines is now archived at

Q1.3) What versions of the ARM processor are there?

The details of various ARM chips and their capabilities are described on Philip Banks web site at

Current developments can be found on ARM Ltd's web site at

Q1.4) What are the differences between different RISC OS versions?

Between RISC OS 2 and RISC OS 3?

A good article on the differences between RISC OS 3 and various versions of RISC OS 3 is available on Richard Goodwins website at

Between RISC OS 3.5 and RISC OS 3.6?

Quite a few, although nothing particularly drastic OS wise, mostly improvements although the lifting of the FileCore partition limit and the incorporation of JPEG handling into the OS are quite substantial improvements. Here is the list :-

Between RISC OS 3.6 and RISC OS 3.7?

Like RISC OS 3.6, RISC OS 3.7 was primarily changed behind the scenes and was an incremental improvement of the OS. The changes were mostly geared towards rendering the OS StrongARM compatible. Here is the list :-

Between RISC OS 3.7 and RISC OS 3.8/4?

RISC OS 3.8 was a developmental version of RISC OS 4 released to developers just before the closure of Acorn's Workstation division and cancellation of the Phoebe project. It was code-named Ursula (see above).

It was finally completed by RISCOS Ltd and RISC OS 4 was the first new version of RISC OS to be released by a company other than Acorn, A comprehensive list of features was released onto their own web site during April 1999. This is available online from

In a nutshell some of the major new features are:-

Between RISC OS 4 and RISC OS 5?

RISC OS 5 was exclusively written by Castle Technology for the Iyonix PC. It was essentially a completely re-written and fully 32-bit version of RISC OS 4.02

A list of features is available online at

RISCOS Ltd maintain a RISC OS 4 FAQ at

Q1.5) What was RISC OS 3.8/Ursula?

Before Acorn decided to abandon Workstations and focus on Digital TV, work was at an advanced stage on an updated version of the operating system (codenamed Ursula) to live in their new machine (Phoebe). Developers had access the RISC OS 3.8 (as Ursula declared itself to be) for evaluation and beta testing purposes. Versions of RISC OS 3.8 were primarily available for ARM710 machines, although some StrongARM compatible versions are known to exist.

For those who don't know, Phoebe is a character from the hit US sit-com Friends, and Ursula is the name of Phoebe's twin sister.

Q1.6) What are the graphics capabilities of RISC OS machines?

This section currently lists the specifications of currently available machines. For the graphics capabilities of older, or legacy, machines, please visit my legacy systems page at

Each type of monitor generally requires a mode definition file (MDF) set up for it, to allow you to take advantage of the specific monitor capabilities. A library of common MDFs can be found at although you'll generally find that with most modern monitors you can find one that works by trying other available MDFs via trial and error.

The Iyonix machines

The most notable difference in the graphics capability of the Iyonix is that it now incorporates a 'standard' graphics card, namely the nVidia GeForce 2MX. This gives much higher resolutions and colour depths than previous 'Acorn' machines, but also sacrifices 2 & 4 bit colour depths (ie. 4 and 16 colour screen modes).

Rather than give an exhaustive list of all 'modes' available, it will suffice to say that the Iyonix display resolutions from 320x200 up to 2048x1536 pixels, each in either 256, 32 thousand or 16 million colours (8, 16 or 24 bit). However the latest nVidia graphics cards do not support 32K colour modes due to the Red and Green components being swapped around.

The A9 Home

The A9 Home has the Samsung ARM9 integreated graphics processor which can drive up to 1600 x 1200 in 16 million colours or 2048 x 1536 in 32 thousand colours.

Q1.7) Is Virtual Memory possible under RISC OS?

The short answer is that full VM is not possible under the current versions of RISC OS. The problem is that most of RISC OS works in SVC mode, if a DataFetch abort occurs then R14_svc is corrupted. This makes returning from the SWI somewhat problematic. This is a hardware limitation with the ARM2 and ARM3 cell chips. Hardware using ARM6 or better processor cells have special memory abort modes that alleviate this problem so future machines and incarnations of RISC OS may well have VM available. Indeed the RiscPC machines make prime candidates for having virtual memory, however there are still re-entrancy issues that make this problematic for RISC OS. (Consider loading data from a file into paged out virtual memory...)

A number of limited solutions were devised over the years but are no longer under development. One such utility was !Virtual by Nick Smith and Ferdinand Oeinck, which allowed VM for a user process using a limited subset of SWI's that are carefully 'protected' against R14_svc being corrupted. This solution suffered from the restricted set of SWI's supported and was mostly useful for batch style processing jobs like compilation or memory intensive processing jobs.

!Virtual v0.37 (and its source) can be downloaded from

Virtualise was developed by Alexander Thoukydides for the Risc PC machines. It was originally sold by Clares Micro Supplies, who's range of products were taken over by APSL in December 2002. Alex's web page giving more information is at

Q1.8) What 'Easter Eggs' are present in RISC OS?

It has been a long tradition with Acorn OSes to have hidden sections that give credit to the people involved in the creation of that OS. The BBC Model B ROMs had the names of the people involved hidden in the memory space occupied by Fred, Jim and Shelia. With the release of the ARM powered machines this tradition has continued on.

RISC OS 2.00

RISC OS 3.00

RISC OS 3.10 & 3.11

RISC OS 3.50

REM Extract Names and Pictures from RISC OS 3.50, 3.60 and 3.70 ROMs
REM Based on an original program (for RISC OS 3.50) by Nick Craig-Wood.
REM Updated by Matt Rix <BigRISC@CyberJunkie.Com>
SYS "OS_Byte",129,0,255 TO ,version%
CASE version% OF
  WHEN &A5: S=&1F47AC :REM RISC OS 3.50
  WHEN &A6: S=&358F18 :REM RISC OS 3.60 - Thanks to Terry Adams for finding this
  WHEN &A7: S=&3A0868 :REM RISC OS 3.70
  OTHERWISE: ERROR 0,"Cannot run on this ROM version.":END
SYS "Squash_Decompress",%1000,-1 TO Q
SYS "Squash_Decompress",%0100,R,S,E-S,P,O TO,,,,,U
run$="Filer_Run "
SYS "OS_File",10,piccy$,&FF9,,P+8,P+P!4+8
SYS "OS_File",10,names$,&FFF,,P+P!4+8,P+O-U
OSCLI "SetType "+piccy$+" Sprite"
OSCLI "SetType "+names$+" Text"
OSCLI run$+piccy$
OSCLI run$+names$

RISC OS 3.60

RISC OS 3.70

RISC OS 3.71

RISC OS 4.02

Q1.9) What is the current status of Linux for Acorn machines?

Due to the rapid development of Linux exact details about the latest incarnation of Linux are not kept in this FAQ. However for the latest information you might like to consult these web pages, or email the people involved with the port :-

Native Linux page :-

The Iyonix machine has a near complete Linux port available for me. Further information can be found at

Peter Naulls has some very useful ARM Linux resources available on his website at

Q1.10) What is the current status of NetBSD for Acorn machines?

N.B. The RiscBSD name has been dropped entirely in favour of NetBSD/arm32.

Due to the rapid development of NetBSD exact details about the latest incarnation of it are not kept in this FAQ. This is a port of NetBSD, a Unix variant, to the RiscPC. However for the latest information you might like to consult these web pages, listen to the NetBSD email list or email the people involved with development of it :-

NetBSD/arm32 - For RiscPC and later machines -

NetBSD/arm26 - For Archimedes and other pre arm600 boxes -

Q1.11) What is Lazy Task Swapping ?

On RISC OS 3.5 and 3.6 machines there were seen to be serious delays in the desktop when running applications with large wimpslots, mostly indicated by the lack of reponsiveness. The problem was identified as being that of having to page in the entire application which, with a 4k page size was quite slow. In RISC OS 3.7 this situation was improved by changing the way in which the application is paged in.

RISC OS 4 can support a new method of paging tasks in - Lazy Task Swapping. This can also be called 'demand paging', because instead of paging the entire space in, individual pages are only given 'on demand'. This means that in a large application only sections of the application space may be physically present although the application itself will be unaware of this.

There is a problem, however, with some versions of the StrongARM processor which will (under certain circumstances) cause Lazy Task Swapping to fail. StrongARMs prior to revision T exhibit this failing and Lazy Task Swapping is consequently be disabled. You may also want to disable Lazy Task swapping if you encounter problems when using DMA.

Index | Part 2 - Upgrades and Expansion

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 Last edit: 10th Apr 2016 at 4:55pm (533 days ago)

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