Retro Tech Week The mid-1980s codebase for RISC OS, the original native OS for the Arm processor, is still run on present-day hardware and actively maintained and developed. We spoke to RISC OS Open MD Steve Revill about its 26-bit origins, working to bring it to newer 32-bit Arm chips, and efforts to update its BSD-based network stack.
RISC OS Open Ltd is the company which ported RISC OS to modern Arm chips for Castle Technology's Iyonix and other hardware.
RISC OS was created at Acorn, the company that in 1981 released the original BBC Micro. Although Acorn never cracked the US market and its machines are little known outside Europe, the BBC Micro was a highly influential machine. The team that designed it went on to create the Arm processor.
Originally codenamed Arthur – short for A RISC by THURsday – it originally appeared on the world's first Arm-powered computer, the Acorn Archimedes, back in 1987. Renamed RISC OS with version 2, it narrowly managed to survive Acorn, and despite some disputes it's still around. In 2018, it was officially open sourced.
As we noted last year, the only other OS from that period that's still around today, NeXTstep descendant Apple macOS, now also runs on Arm hardware: the M1 and M2 Macs.
While macOS is a Unix, an OS with its roots in the 1960s, RISC OS is something else: its core hand-coded in assembler, tiny and very fast, and still only supporting its original processor architecture – but today, that's the most widely used CPU architecture in the world.
Liam Proven (LP): So hello, and welcome to Retro Tech Week on The Register. I'm Liam Proven. I'm the FOSS and open source and public cloud correspondent for The Register. And joining me today is Steve Revill of RISC OS Open. Steve, thank you very much for coming. Would you like to introduce yourself?
Steve Revill (SR): Yes, sure. So I am the director of a company called RISC OS Open. We were formed in about 2006. We all came from a background in a company that was British-based called Acorn Computers. And we're very passionate about open source. So I'm very pleased to be sat here talking to you today.
LP: So um, yeah, thank you very much because I do have and use RISC OS myself. I have both Pi 400, and because I'm moving house quite soon, in its box, a 4 and a 400 sitting here, that has RISC OS on it.
So RISC OS was the original native operating system for the Arm chip, and came out of Acorn Computers who invented the Arm. How come RISC OS is open source these days?
SR: Well, back in the its origins, RISC OS was a proprietary operating system owned by Acorn Computers – developed by, as you said, the same people who developed the Arm chip. The Arm architecture... went off on its own path with involvement from various companies, notably Apple, but eventually it was spun out on its own to dominate the world. And RISC OS stayed as an internal project within Acorn Computers, and around the end of the '90s Acorn Computers was taken over.
And RISC OS largely became a forgotten project. But there were a lot of people who worked on RISC OS in the past, who felt passionately that this was a significant milestone in British computing history, its origins being tied so closely to the Arm architecture, and so we believed that it needed to have some sort of preservation.
And at the time, late '90s, early noughties, there was a lot of growing exposure of open source around the world, and especially Linux was certainly taking off and starting to take over. And we believe that open source was the way forward for the preservation, at the very least, of this piece of computing history.
And we negotiated with a company that took over RISC OS from Acorn called Castle Technology. We negotiated quite hard with them for many years, and eventually around 2006 We agreed with them that we would form a company called RISC OS Open and they would publish the source code for RISC OS under a permissive license that still not closed source, but it's not open source. It's somewhere in the middle. And that was called a shared source license, which was written from scratch, with lawyers, very expensively, when when I think we could have just picked an open source license off the shelf.
But one thing they were very concerned about was making sure that any work that was done on RISC OS they could stand to benefit from it financially because they'd invested quite a lot in buying the technology from its owners.
And our job as RISC OS Open was to do the grunt work and help Castle to relicense all of the source code under their shared source license. And that was an entertaining process. It was a part archaeology, finding out who owns the rights to various bits, are they still alive? Do they still remember anything about it?
Maybe it's companies that have been taken over several times and trying to agree sensible licensing terms for everything that we are publishing. And then it's trawling through the code itself and saying, is this suitable for release to the world?
Because you can imagine a closed source private piece of software. There's a lot of developers and there are a lot of pressures sometimes. They might write things in their code that you perhaps don't want publishing.
LP: Take out all the swear words!
SR: Yeah, that's correct. Any people insulting other people? So we even, we wrote custom code just to scan the code base for things that might be considered offensive, stuff like that to us. And it wasn't it was a very long multi year project with a small group of about four people really, all either ex-Acorn, or from the Acorn sphere of influence. And we're all software engineers. And we, piece by piece, published the source code and the Castle shared source license. And that was really that was the first step of a much more ambitious and longer journey.
LP: So now correct me if I'm wrong, I've been following the world of Acorn and Arm for... well, since since since, you know before the Arm was launched, I could never afford a BBC Micro in the day. But the thing that came out of Pace and getting the code from Pace was the Iyonix. That was kind of the first new product from Castle, wasn't it? Because they continued making some of the original Acorn hardware like the RISC PC, but the Iyonix was a whole new computer with an Intel-made Arm chip that didn't have the 24-bit mode, that Acorn used?
SR: The 26 bit. That's right. So there was a small group of us who many went on to become RISC OS Open in the demise of Acorn, and we eventually formed a small company called... oh, what was it called? I forget what it was even called now. Somatic, that's the one. We offered professional services and Castle who had bought RISC OS, needed a company to help them develop the next generation of Acorn, RISC OS computer, because they didn't just want to keep selling legacy hardware until eventually the whole market disappeared.
They wanted to spur ongoing development and ongoing growth in the market. So the Iyonix was born from a collaboration between Somatic and Castle technology. And as you said, architecturally, the chipset was passing an important milestone in Arm's history, whereas a lot of its legacy addressing mode – 26 bit mode – was thrown in the waste bin and everything was fully 32-bit. And for RISC OS it was a big problem. Because a lot of RISC OS and the applications that run on RISC OS were written in 26 bit mode, and they just wouldn't run on this chip. Now, before Castle took over acorn and pace had been aware of this change coming and a lot of work had been happening but it had never been finished.
And so there was a rush to get all of that work finished and alongside the launch of the Iyonix but it was an important step because that's opened the doors to everything that's that's happened subsequently.
LP: Okay. Okay. And, and so, that led, I think it was called, that was the sort of dawn of RISC OS five, is that right? That was like the 32 bit version.
SR: That was the beginning of RISC OS five, yes.
LP: Yeah. And, and that's the form that's now the now is open source. So now is is is rule risk is that there is another one, there is this other fork, but now I've written a bit about RISC OS on the rage recently, and I talked to the guy behind risk averse development, Andrew Ronsley. And he told me that as far as he knows that that sort of fork of it is pretty much dead now that there hasn't been any new development on it in
SR: That's right.
LP: That was mainly aimed at selling upgrades to existing acorn machine owners back in the day. And now it's owned by this company that sell an acorn emulator. So it's sort of aimed at the legacy side. And really RISC OS five is is the only version that's kind of going forward and developing. You run on the on the Raspberry Pi. But that is not by any means the only platform. It obviously only runs on ARM processors, but you run on various other machines as well. Isn't that right?
SR: That's correct. So as well as the legacy platforms that came out of the acorn era, and the iyonix that came from Castle they've been subsequent devices built from the ground up for RISC OS, such as the titanium, which is from a company called LSR. And that uses a much more modern chipset.
And then there's a lot of essentially open hardware platforms or close to open hardware platforms such as the OMAP range. And that's like the BeagleBoard the PandaBoard that I get five. So there's those platforms that we've ported to. There's the i MX six board, the wand board, and the pinebook. And we also have some ports to some more esoteric platforms that are a bit rough and ready, like Psion notebooks and various other products. I do they're probably not feature complete. Probably not as poli Source: The register