Liam Proven (liam_on_linux) wrote,
Liam Proven

Was Acorn's RISC OS an under-appreciated pearl of OS design?

I was a huge Archimedes fan and still have an A310, an A5000, a RiscPC and a RasPi running RISC OS.

But no, I have to disagree. RISC OS was a hastily-done rescue effort after Acorn PARC failed to make ARX work well enough. I helped to arrange this talk by the project lead a few years ago.

RISC OS is a lovely little OS and a joy to use, but it's not very stable. It has no worthwhile memory protection, no virtual memory, no multi-processor support, and true preemptive multitasking is a sort of bolted-on extra (the Task Window). When someone tried to add pre-emption, it broke a lot of existing apps.

It was not some industry-changing work of excellence that would have disrupted everything. It was just barely good enough. Even after 33 years, it doesn't have wifi or bluetooth support, for instance, and although efforts are going on to add multi-processor support, it's a huge amount of work for little gain. There are a whole bunch of memory size limits in RISC OS as it is -- apps using >512MB RAM are very difficult and that requires hackery.

IMHO what Acorn should have done is refocus on laptops for a while -- they could have made world-beating thin, light, long-life, passively-cooled laptops in the late 1990s. Meanwhile, worked with Be on BeOS for a multiprocessor Risc PC 2. I elaborated on that here on this blog.

But RISC OS was already a limitation by 1996 when NT4 came out.

I've learned from Reddit that David Braben (author of Elite and the Archimedes' stunning "Lander" demo and Zarch game) offered to add enhancements to BBC BASIC to make it easier to write games. Acorn declined. Apparently, Sony was also interested in licensing the ARM and RISC OS for a games console -- probably the PS1 -- but Acorn declined. I had no idea. I thought the only 3rd party uses of RISC OS were NCs and STBs. Acorn's platform was, at the time, almost uniquely suitable for this -- a useful Internet client on a diskless machine.

The interesting question, perhaps, is the balance between pragmatic minimalism as opposed to wilful small-mindedness.

I really recommend the Chaos Computer Congress Ultimate Archimedes talk on this subject.

There's a bunch of stuff in the original ARM2/IOC/VIDC/MEMC design (e.g. no DMA, e.g. the 26-bit Program Counter register) that looks odd but reflects pragmatic decisions about simplicity and cost above all else... but a bit like the Amiga design, one year's inspired design decision may turn out, a few years later, to be a horrible millstone around the team's neck. Even the cacheless design which was carefully tuned to the access speeds of mid-1990s FP-mode DRAM.

They achieved greatness by leaving a lot out -- but not just from some sense of conceptual purity. Acorn's Steve Furber said it best: "Acorn gave us two things that nobody else had. No people and no money."

Acorn implemented their new computer on four small, super-simple, chips and a minimalist design, not because they wanted to, but because it was a design team of about a dozen people and almost no budget. They found elegant work-arounds and came up with a clever design because that's all they could do.

I think it may not be a coincidence that a design that was based on COTS parts and components, assembled into an expensive, limited whole eventually evolved into the backbone of the entire computer industry. It was poorly integrated but that meant that parts could be removed and replaced without breaking the whole: the CPU, the display, the storage subsystems, the memory subsystem, in the end the entire motherboard logic and expansion bus.

I refer, of course, to the IBM PC design. It was poor then, but now it's the state of the art. All the better-integrated designs with better CPUs are gone, all the tiny OSes with amazing performance and abilities in a tiny space are gone.

When someone added proper pre-emptive multitasking to RISC OS, it could no longer run most existing apps. If CBM had added 68030 memory management to AmigaOS, it would have broken inter-app communication.

Actually, the much-maligned Atari ST's TOS got further, with each module re-implemented by different teams in order to give it better display support, multitasking etc. while remaining compatible. TOS became MINT -- Mint Is Not TOS -- and then MINT became TOS 4. It also became the proprietary MaGiC OS-in-a-VM for Mac and PC, and later, volunteers integrated 3rd party modules to create a fully GPL edition, AFROS.

But it doesn't take full advantage of later CPUs and so on -- partly because Atari didn't.
Apple famously tried to improve MacOS into something with proper multitasking, nearly went bankrupt doing so, bought their co-founder's company NeXT and ended up totally dumping their own OS, frameworks, APIs and tooling -- and most of the developers -- and switching to a UNIX.

Sony could doubtless have done wonderful stuff with RISC OS on a games console -- but note that the Playstation 4 runs Orbis, which is based on FreeBSD 9, but none of Sony's improvements have made it back to FreeBSD.

Apple macOS is also in part based on FreeBSD, and none of its improvements have made it back upstream. macOS has a better init system, launchd, and a networked metadata directory, netinfo, and a fantastic PDF-based display server, Quartz, as well as some radical filesystem tech.
You won't find any of that in FreeBSD. It may have some driver stuff but the PC version is the same ugly old UNIX OS.

If Acorn made its BASIC into a games engine, that would have reduced its legitimacy in the sciences market. Gamers don't buy expensive kit, universities and laboratories do. Games consoles sell at a loss, like inkjet printers -- the makers earn a profit on the games or ink cartridges. It's called the Gilette razors model.

As a keen user, it greatly saddened me when Acorn closed down its workstations division, but the OS was by then a huge handicap, and there simply wasn't an available replacement by then. As I noted in that blog post I linked to, they could have done attractive laptops, but it wouldn't have helped workstation sales, not back then.

The Phoebe, the cancelled RISC PC 2, had PCI and dual-processor support. Acorn could have sold SMP PCs way cheaper than any x86 vendor, for most of whom the CPU was the single most expensive component. But it wasn't an option, because RISC OS couldn't use 2 CPUs and still can't. If they'd licensed BeOS, and maybe saved Be, who knows -- a decade as the world's leading vendor of inexpensive multiprocessor workstations doesn't sound so bad -- well, the resultant machines would have been very nice, but they wouldn't be RISC PCs because they wouldn't run Archimedes apps, and in 1998 the overheads of running RISC OS in a VM would have been prohibitive. Apple made it work, but some 5 years later, when it was normal for a desktop Mac to come with 128MB or 256MB of RAM and a few gigs of disk, and it was doable to load a 32-64MB VM with another few hundred megs of legacy OS in it. That was rather less true in 1997 or 1998, when a high-end PC had 32 or 64MB of RAM, a gig of disk, and could only take a single CPU running at a couple of hundred megahertz.

I reckon Acorn and Be could have done it -- BeOS was tiny and fast, RISC OS was positively minute and blisteringly fast -- but whether they could have done it in time to save them both is much more doubtful.
I'd love to have seen it. I think there was a niche there. I'm a huge admirer of Neal Stephenson and his seminal essay In The Beginning Was The Command Line is essential reading. It dissects some of the reasons Unix is the way it is and accurately depicts Linux as the marvel it was around the turn of the century. He lauds BeOS, and rightly so. Few ever saw it but it was breathtaking at the time.

Amiga fans loved their machine, not only for its graphics and sound, but multitasking too. This rather cheesy 1987 video does show why...

Just a couple of years later, the Archimedes did pretty much all that and more and it did it with raw CPU grunt, not fancy chips. There are reasons its OS is still alive and still in use. Now, it runs on a mass-market £25 computer. AmigaOS is still around, but all the old apps only run under emulation and it runs on niche kit that costs 5-10x more than a PC of comparable spec.

A decade later, PCs had taken over and were stale and boring. Sluggish and unresponsive despite their immense power. Acorn computers weren't, but x86 PCs were by then significantly more powerful, had true preemptive multitasking, built-in networking and WWW capabilities and so on. But no pizazz. They chugged. They were boring office kit, and they felt like it.

But take a vanilla PC and put BeOS on it, and suddenly, it booted in seconds, ran dozens of apps with ease without flicker or hesitation, played back multiple video streams while rendering them onto OpenGL 3D solids. And, like the Archimedes did a decade before, all in software, without hardware acceleration. All the Amiga's "wow factor" long after we'd given up ever seeing it again.

This, at the time when Linux hadn't even got a free desktop GUI yet, required hand-tuning thousands of lines of config files like OS/2 at its worst, and had no productivity apps.

But would this have been enough to keep A&B going until mass-market multi-core x86 chips came along and stomped them? Honestly, I really doubt it. If Apple had bought Be, it would have got a lovely next-gen OS, but it wouldn't have got Steve Jobs, and it wouldn't have been able to tempt classic MacOS devs to the new OS with amazing next-gen dev tools. I reckon it would have died not long after.

If Acorn and Be had done a deal, or merged or whatever, would there have been enough appeal in the cheapest dual-processor RISC workstation, with amazing media abilities, in the industry? (Presumably, soon after, quad-CPU and even 6- or 8- CPU boxes.)

I hate to admit it, but I really doubt it.
Tags: acorn, amiga, amigaos, apple, arm, risc os, st

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