Historical Operating Systems Reborn – RISC OS and the Raspberry Pi

The early-1980s 8-bit microcomputer battle brought the personal computer from a hobbyist’s plaything to a genuinely useful device for general use, and was fought by a host of companies. Most of these companies were from the United States, such as Commodore, IBM, Apple and Atari, but various British companies played a significant part including Sinclair, Amstrad and Acorn. By the mid-1980s, many of the smaller competitors had fallen by the wayside, and even the once-strong Sinclair Research had been bought up by Amstrad.

The big players who remained decided to produce more powerful machines using newer processors than the MOS 6502 and Zilog Z80 8-bit processors common in the early 1980s. Commodore bought up the Amiga Corporation, which had designed an eponymous computer; Apple designed the Macintosh; Atari developed the Atari ST and IBM continued to develop on their IBM PC platform. Most of these computer designs, with the notable exception of the IBM PC, were based around the Motorola 68000 processor. As Amstrad decided to focus on their PCW series of word processors, discontinuing the disappointing Sinclair QL, this left Acorn alone in the British market to try to fight out the battle of the post-8-bit era.

Acorn decided to take a different approach to the American companies, focusing on the educational segment rather than the business, desktop publishing and multimedia markets focused on by Commodore, Apple, Atari and IBM. Instead of using the Motorola 68000 processor familiar to other computers of the time, Acorn decided to design their own processor, using the then-novel RISC architectural design to develop the Acorn RISC Machine processor, better known as ARM.

In 1987, Acorn released the Archimedes. The ARM2 processor which Acorn used proved to be a great advantage for the Archimedes, with a simple, power-efficient design which nevertheless performed calculations about twice as quickly as a 68000 processor with the same clock speed. Allied to the ARM processor was Acorn’s Arthur operating system, which came on a ROM chip similar to the Amiga’s Kickstart ROM. Arthur, on balance, was on par or not far behind the Commodore Amiga’s notoriously advanced OS, and ahead of the single-tasking operating systems used by Atari and IBM.


The Acorn Archimedes – one of the several advanced computers of the late 1980s.

Unfortunately for Acorn, the Archimedes was not a particular sales success. Its focus on the educational market had come at the cost of the multimedia coprocessors available in the Amiga and Atari ST, leading to a system that was too expensive and not good enough at gaming for a home audience. Meanwhile, the business market became consumed by IBM and the various clones which arose from the easily-reverse-engineered BIOS of the IBM PC and its successors. Nevertheless, Acorn persisted and continued to develop new machines with more advanced operating systems. Arthur was updated, becoming RISC OS in the process, keeping to the same general structure but gaining new features.

Eventually, Acorn fell to the wayside, suffering a similar ignominious fate to Commodore and Atari as the personal computer market gradually became dominated by IBM-compatible computers with Intel processors. Apple managed to cling onto life during some very slim years, moving to the PowerPC architecture along the way, but eventually gave in and took up the Intel x86 processors as well, moving their BSD-derived Mac OS X operating system over to the new architecture.

Acorn has had one significant lasting legacy, however – the intellectual properties for the ARM processor were divested in a new company, ARM Holdings, who collaborated with Apple to continue developing the ARM architecture for Apple’s own devices. Today, the ARM processor is the most popular 32-bit processor architecture in the world, underpinning everything from smartphones and tablets to embedded processors inside other devices.

RISC OS has survived as well, with the intellectual property for the Acorn computers sold to Castle Technology Ltd., a small British company who has continued to develop ARM-based personal computers using RISC OS. A small but dedicated community grew up around the company, much like the remnants of the Amiga or Atari ST communities, and has continued to support the OS.

Now, we have the Raspberry Pi. The inexpensive, credit-card-sized computer has been a massive success, demonstrating a far more simple, hackable approach to computing than has been usual today. Something that has been a pleasant surprise is how readily the RISC OS community has decided to support the Raspberry Pi.

Given that until recently, I haven’t had a computer without an Intel processor, I didn’t have an opportunity to try RISC OS on anything but an emulator. However, I sometimes despair for the sheer homogeneity of the personal computer market, even though I have contributed to it for many years. Now, I have been granted a chance to try an operating system natively on modern hardware that isn’t part of the Microsoft Windows, Mac OS X or Linux families.

My initial thoughts when I first booted up RISC OS 5 were that it actually boots up as astoundingly quickly as others said it would. Frankly, this shouldn’t have been a surprise; not only is RISC OS still designed with the StrongARM processors of the Acorn Risc PC in mind, it is still developed for a 6MB ROM chip, and is therefore extraordinarily tuned for its environment. I had used RISC OS before on the ArcEm emulator about four years ago, so I recognised that RISC OS was slim and fast in the early 1990s, but it’s nice to see that this behaviour persists today. The same sort of responsiveness applies to the shutdown process as well. RISC OS has instant shutdowns. None of this behaviour where shutdowns can take almost as long as the boot process – as soon as you click the Shutdown option, short of certain file operations being in progress, the computer will immediately be ready to shut down.

After about ten to fifteen seconds, the GUI environment booted up. Two things were quickly apparent. The first is that the environment was immediately responsive as soon as it had finished loading, unlike contemporary Windows or Linux desktop environments, which, based on the number of background processes that are set to start – can leave you waiting a minute or more for full responsiveness.

The second thing is that the RISC OS GUI environment is, in fact, very pretty. Mac OS X and iOS are often held up as being the exemplars of pretty environments, but I’d argue that RISC OS is, in its own ways, marginally prettier. Much of what Mac OS X does to ensure its pretty environment is down to impressive, shiny graphics and high-resolution displays, whereas RISC OS manages to look good at 640×480 on a simple non-high-definition television screen.

A lot of this is down to the inherent design philosophy of RISC OS. The original Arthur OS for the Archimedes was the first operating system to incorporate a dock, or in RISC OS parlance, an icon bar. The icon bar distinguishes between application icons, set to the right-hand side of the icon bar, and storage devices, set to the left-hand side of the bar. This helps to create a distinct divide between applications and devices which store applications and data. In comparison, the Mac OS X dock can occasionally look a bit untidy and busy when you load up too many applications at once.

Another detail in RISC OS’s favour in the design stakes is the high-quality anti-aliasing technology that has been a part of the operating system since 1989. The renderer is designed, as are some of the more recently designed competing technologies available in other operating systems, to render type accurately at the cost of readability, but frankly, even at the 640×480 resolution I have been using, the typefaces still look clean and legible, which helps make the interface look clean and stylish.


RISC OS – stylish even at low resolutions, even better in high definition.

Enough about the style – how about the substance? It turns out that you get quite a few things even from your 6MB ROM image, including the full GUI environment, a text editor, a vector graphics program, a simple scientific calculator and a BBC BASIC interpreter.

Of course, it seems awfully odd and antediluvian to be supporting a BASIC interpreter in 2013, but BBC BASIC was one of the most sophisticated BASIC interpreters of its time and was extended with its move to RISC OS with capacity to write full, multitasking GUI applications. BBC BASIC is also one of the most optimised and rapid interpreted languages on any platform, proving sufficiently quick for the entire Arthur GUI interface to be written in it. The interpreter also includes capacity for inline ARM assembly language, providing a low-level programming environment inherent to the system. Few other operating systems actually have any inherent capacity for programming, and while Linux, Mac OS X and other Unix and Unix-like operating systems typically have programmability through their command shell, this isn’t going to fit in 6MB along with a GUI environment.

Unfortunately, when it comes to other applications, RISC OS currently looks a bit sparse. Given that the operating system has been maintained by a single, small company and kept alive mainly by hobbyists, this is to be expected, but you’re certainly not going to have the wealth of software that you have on Linux or Mac OS X, let alone Windows. This may improve if the community grows with the popularity of the Raspberry Pi, but it will prove difficult to use RISC OS for most serious work right now.

From a technical perspective, RISC OS is a very different beast to the three most popular desktop operating systems. Microsoft Windows comes from a lineage that incorporates elements of CP/M, OpenVMS and so on, while Mac OS X and Linux are obviously derived from Unix. RISC OS doesn’t derive from either lineage – or from any other apparent one either. Directory paths are delineated by full stops rather than slashes, for instance. Disc formatting uses the proprietary ADFS system first developed for the BBC Micro. Files don’t have extensions as default, with the file type determined by a six-byte file type number stored separately, and when extensions are used, perhaps from imported files from another operating system, the extension is delineated from the name by a forward slash.

One of the most distinctive details of RISC OS is how it deals with applications. Application names always begin with an exclamation mark, and RISC OS applications more closely represent directories in other operating systems than they do the executable files of Windows or Linux. In fact, RISC OS applications are extraordinarily modular in nature – you never have to “install” an application on RISC OS as you would in Windows, and you can just drag an application icon onto the icon bar to open it.

Another particularly distinctive detail of RISC OS comes from the way it handles the mouse. Acorn designed the Archimedes with a three-button mouse from the very start, and each of the buttons on the mouse have very individual functions. Unlike Windows, Mac OS X or Linux – or most other desktop GUI systems – RISC OS has a separate Menu button set to the middle button, and therefore, applications are not expected to have a program-specific menu bar, or a Ribbon interface or anything like that. The middle button performs menu tasks in every application, including the ones normally done by the right mouse button in Windows or Linux.

The other two button functions are Select, set to the left mouse button and performing tasks similar to the left mouse button in other desktop operating systems, and Adjust, set to the right mouse button. Adjust performs various functions, ranging from an alternate way to perform various tasks in most programs to an alternate menu for some application icons.

There are some places where RISC OS betrays its Eighties origin, though, and not necessarily in a good way. RISC OS uses cooperative multitasking rather than the pre-emptive multitasking common in operating systems from Unix to Microsoft Windows to AmigaOS and others besides. I have, in the past, been quite disparaging about the use of cooperative multitasking in any operating system, including RISC OS, and using RISC OS, it’s clear that it is an underlying disadvantage of the system.

I’m quite fond of pushing my systems to the limit when it comes to multitasking – it’s common for me to have a web browser, a word processor, a music player, a PDF reader and the file manager for my operating system all open at one time, with other tasks perhaps happening in the background. With a pre-emptive multitasking system, the programs are given a fair share of the computer’s free time, only occasionally locking up because one task is a bit too greedy with the clock cycles. With a cooperative multitasking system, it’s more difficult to run multiple applications at once, since one program that is badly designed or simply resource-heavy can lock up the system until it resolves. Using RISC OS for multimedia applications at the same time as performing a processor-heavy task is therefore a potential no-go area, which is a pity considering how smoothly the system runs on a single task.

Mostly, though, I like how different RISC OS 5 feels to other contemporary operating systems. Certain technical details, such as the obsolete cooperative multitasking model, make it difficult to recommend for everyday use right now, while the relative lack of applications also works against it. However, being allied to the Raspberry Pi could well give RISC OS a renewed lease of life, especially in the educational sector where it would be perfect for demonstrating that not every operating system is, or even has to be, the same as Windows or Mac OS X. In that sense, the OS could come full circle – from its educational roots right back around to them again.