Various versions of RISC OS I've used.

Published , updated by Richard GoodwinFiled under Computers

RISC OS is the name of the operating system for Acorn's ARM-powered desktop computers.  It's what I used from college until well in to my coding/web development career.  A nice, simple OS that was held in ROM so a computer could get to the desktop quickly and be usable even without a hard drive fitted.


This is the forerunner to RISC OS. When the Archimedes series was first introduced RISC OS wasn't ready, so this fairly basic version was what got shipped with the early machines. In some respects it resembles the desktop that was included on the BBC Master Compact series welcome disc - the Master Compact also being close to the Archimedes in the split design (keyboard and base unit were joined by a wire, not in one unit), and the floppy drives were 3.5" ADFS drives rather than the more familiar 5.25" DFS drives used on most BBC and BBC Master machines. The official Acorn Electron floppy disc unit, the Plus 3, also contained a 3.5" ADFS drive, so it had been on the cards for a while.

Computer Concepts decided to write their own OS to replace Arthur, but RISC OS was finally released just ahead of theirs. Part of this alternative project however surfaced as the Impulse module in Impression etc. for communication between different parts of the CC range - to enable mail merge and so on.

As you can see from the screenshots, although some simple programs were included on the desktop it is not possible to do much without loading things from disc - there's no bitmap editor (although a rather groovy pre-Paint monotasking bitmap editor was available from disc), and to get a screenshot I had to get the floppy drive working and write a one-line BASIC program on my RiscPC to do the equivalent of *screenshot. You might also notice that although I've tried to correct the time, the date seems stuck in 1989.

Never mind that this machine is pretty much useless, this particular unit (base and keyboard only) was bought off eBay for just £1.50 (P&P £10). A listing of an Archimedes with a "funny coloured desktop" tipped me off that it might contain this now rare OS. The machine itself is an A310 with THE EXTRA scratched along one side, so presumably it has been sat in a cupboard as a potential source for spares for a while until it was made available for sale, hence the lack of upgrading to RISC OS 2 or 3.

*help - click to see what's in Arthur.


After ArthurOS came RISC OS 2, the first proper multitasking OS for the Archimedes range. RISC OS traditionally comes in ROM form, so that's four chips to unsocket and change.

Gone is the rather horrendous orange/blue colour scheme, to be replaced with a more sedate grey theme; the desktop palette was eight shades of grey followed by a range of eight colours, a fairly decent spread although purples and magentas are hard to reproduce even with dithering.

256 (fixed) colour desktops were also possible, with 64 colours in four shades, but window furniture and filer icons had to fit in with the 16 colour palette (256 colour filer icons tended to look corrupted in 16 colour desktops as the filer display routine didn't take the current mode into account until RISC OS 3).

RISC OS 2 introduced some staples that are still with us today; unlike ArthurOS you could add new programs to the iconbar along the bottom (a feature that Windows was to replicate years later). To keep track of all of these programs and generally manage resources such as the size of the RAM disc the Task Manager was introduced, represented here as an "A" icon, the Archimedes logo. This would later be replaced by Acorn's own logo in RISC OS 3.

Most programs just displayed their memory usage and could be killed from here as well as through the program itself; with some programs, and especially the resources sections, you just dragged the bars to the required level. So for instance, the RAM disc was created by dragging the corresponding bar from 0K to, say, 160K; if that wasn't right, so long as the disc was empty, you could resize it to your hearts content. Later third party hacks allowed it to resize while full, or even auto-resize as needed.

The palette utility allowed you to change to numbered modes - 12 was a 16 colour low resolution mode, 15 was the same in 256 colours, and so on. You could also change the desktop palette to any 16 from 4096, and I think the greyscales were linked so changing the first or eighth colour would interpolate the other six "greys" for a nice spread. This has all been changed so that you just choose colours and resolutions and the correct mode is worked out, and the palette editor has gone (which is why I wrote my own palette utilities).

*help - see what's in RISC OS 2.

Many thanks to Martyn Fox for some of the screenshots used in this part of the website. The images were taken from Martyn's book, First Steps in Programming Acorn RISC OS Computers.


RISC OS 3 was, unsuprisingly, the upgrade from RISC OS 2, which in turn was the first proper RISC OS after ArthurOS. RISC OS 2 came fitted in my A310, and being a poor student/layabout at the time I didn't really want to upgrade - until so much new software and PD came out that was RO3 only I had to.

RISC OS 3.0 came with the new A5000 computers, but was quite buggy - not a big surprise as it came on EPROM, so someone knew there'd be an upgrade not long after release. RISC OS 3.10 was the first upgrade, and I waited so long that 3.11 was available by the time I got round to it. I still didn't stump up full whack though, I was so cheap I said I had an A5000 and just paid the upgrade price. I still had to pay for a header card though.

RISC OS 3.11

Here's plain old RISC OS 3.11 after a clean reset. It has a 16 colour desktop at 640x256, although as the vertical pixels are rectangular it's the same apparent size as 640x512 which gave higher apparent resolutions for small amounts of memory (and kept the monitor s cheap). This rectangular pixel stuff first came into play with the 8bit machines like the BBC B for display on a TV without the need for interlacing, and of course there was the 32K memory limit - although this 32bit machine has been upgraded from 1MB to 4MB. This A310 is capable of proper 640x512 but came with a low-res monitor.

This machine also has an IDE hard drive fitted (called Cromwell, bottom left), which isn't standard on my A310 - although the 400 series had ST506 hard drives, the 300 series didn't, so I added a third party interface.

The main difference between the look of RISC OS 3 and RISC OS 2 is the addition of an Apps folder on the desktop. This contains programs and resources built into te ROM-based OS, so you always have a text editor, painting package etc. available even without any disks. RISC OS 2 had similar programs, but only if you had the Applications discs. The yellow and blue A task manager icon is now a green acorn too.

Living with RISC OS 3.11

My usual RISC OS 3 desktop. It's still not awe-inspiring by today's standards, but it has funkier icons including individual directory icons and antialiased filer text (these latter two using one small third-party patch module called Desktop+). The window furniture is in 3D too, although I have a plain pinboard to maximize the available memory. The screen mode is 256 colours with a hacked 832x288 (832x576) size. Note the virtual 24bpp colour display being shown using the built-in ColourTrans dithering.

As the boot sequence has been allowed to run you can see that this machine is on a network - Trinity is a remote drive accessed by an ancient Samba-like protocol called ShareFS. This particular machine is on a standard 10baseT, TCP/IP network, although older Econet networks were more common in schools.

Configuration and Maintenance

One of the really nice things about RISC OS - apart from the easy-to-use GUI - is how easy it is to configure and maintain. The task manager gives a visual list of all running applications and other programs, and allows you to kill running processes or allocate more memory. For instance, if you need a RAM disk just click next to the RAM disc section and drag the red bar to the desired size, and a RAM disk appears.

Although a command line is available at all times from the desktop - or most text editors support Task Windows, which does the same thing in a window like Linux desktops - there's also a configuration application that allows you to do the same job more easily.

This might not seem revolutionary now, but RISC OS 3.11 is ©1992, and many of these features date back to even earlier versions of the OS!

Later versions of RISC OS 3

The RiscPC range came with later versions of RISC OS 3 installed - 3.5 was the first, then 3.6 with later machines, then 3.7 was introduced with support for StrongARM processors and fixing some brokeness that had crept in. The differences from a look and feel point of view were minor - a proper mode selection utility with colour and resolution rather than arbitrary mode numbers for instance - but added support for the new processors, disc controllers, graphics and sound chips, and, well, pretty much everything.

RISC OS 3.8 was available as a softloadable upgrade for developers to see how the new version would work on the RiscPC v2 (aka the Phoebe), which finally introduced things like very large hard disc support, long filenames (previously we'd been relying on a third party hack!), more than 77 files in a directory etc. However, Phoebe crashed and burned, taking Acorn with it, and then RISCOS Ltd. came along with RISC OS 4...


RISC OS 3.5 was the first official RiscPC OS, required to handle all the new stuff like VIDC20 graphics, 30Mhz ARM 6 processors and the like; 3.6 added support for slightly faster processors (33Mhz ARM 6, 40Mhz ARM 7); 3.7 fixed a number of bugs in 3.6 (including the one that would screw up your hard drive if you had a directory cache set and saved lots of small files, like in some news readers), plus brought support for the the 200Mhz StrongARM developed in conjunction with Digital (DEC).

3.8 was an unreleased beta (unless you knew the right people) that became RISC OS 4, and removed certain restrictions like the 77 files in a directory, 10 character file name, huge LFAU making any drive over 2GB uneconomic and so on. Some of those restrictions could be gotten around using third party hacks, but there's nothing like having it built into the OS.

I got so in to changing the desktop look and feel that I wrote some software to automate it, my RISC OS Theme Manager.

Other versions of RISC OS

There were - are - a number of other versions of RISC OS after 4, but that's pretty much where my journey ended.  There were, at one point, two competing versions, but a combination of job changes and alterations to how RISC OS handled its boot sequence meant I started to drift away both professionally and as a hobbyist.  Eventually the acid leaked out of the battery back-up and ate away at my RiscPCs until I couldn't use them any more anyway.

That is until the Raspberry Pi came out, which could run RISC OS well enough to copy the contents of my old hard drive onto a memory card (my whole hard drive on one tiny card! Progress!) and then I used an emulator on a Windows PC to convert old file formats into more modern, usable ones.  The old me would probably be horrified but I'm just pleased to have all my old stuff back.