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The RiscPC is 20 years old!

April 15th 1994. That's the day when the project known as "Medusa" was unveiled to the world. The RiscPC. Acorn's most powerful computer yet, and - ultimately - the most powerful they ever made.
Setting an interesting direction, the system memory was one or two plug-in SIMMs. Free of the MEMC's 4Mb restriction, you could fit hundreds of megabytes. I don't recall if it topped out at 128MB or 256MB; but given that I have a 256MB Pi and it usually tells me that I have around 200MB free (after the GPU has laid claim to 32), I don't think that would matter for many users.
Graphics memory could be separate from system memory, and that was a plug-in module too. The new VIDC offered millions of colours and fairly arbitrary monitor definitions that could be loaded from "MDFs", mode definition files. No more writing weird modules to support a specific monitor, just make an MDF. You could have up to about 1600×1200, however since the largest VRAM was 2MB, it was a trade-off between "big" or "many colours".
Better yet, the processor itself was a plug-in module. Want a faster computer? Just plug in a new processor.
That's not all. There were two processor slots. The second was for something quite alien. An Intel 80486! It could run Windows 3.11 like a breeze, but better yet it could even manage Windows95. With nothing more than an x86, a big ASIC, and some really clever software, a RiscPC could host a perfectly worthwhile PC environment.

The computer was supplied with the usual not-particularly-big IDE harddisc and a high density 3.5" floppy. This was supplied in a squat box not unlike an A5000 in size. But, wait for it, yet more novel ideas. The first was a sliding flap to hide the floppy drive and CD-ROM if you had one. A nicely curved fascia that slid down out of the way. But we aren't done yet. The standard RiscPC could only accept two expansion podules. That's not a lot. There was also not much room for extra harddiscs and such. Solution? Flip outward the four toggle catches at each corner, lift off the lid, stack up another 'slice'. Optionally fit a larger backplane. My RiscPC is a two-slicer. You could go for more, up to six, to turn a standard RiscPC into something rather insane. Speaking of which, the RiscPC at that year's Acorn World Show featured a toaster in it's top slice. Me? I'd have gone for a coffee maker, but I guess Acorn decided crumbs on the motherboard was less grief than coffee.

Fitting only into 2MB, the original RISC OS 3.5 ROM was... interesting yet disappointing. A little like RISC OS 2, the ROM apps and the things that made it useful were missing. It was, to be honest, a rejigged version of 3.1x to support the newer hardware.
That was followed by RISC OS 3.6 which brought the apps back into the ROM, and then RISC OS 3.7 which improved compatibility and made task swapping quite a bit better. It also had a decent internet stack on-board at least.

In terms of hardware, the ARMv3 (ARM610, ARM710) were huge leaps forward given that they supported the original 26 bit PC+PSR mode, and the new ARM mode that was 32 bit. Not that Acorn ever bothered to make RISC OS 32 bit. I think they figured that by and large you could buy a RiscPC and plug all your old stuff into it and "it will just work", and pretty much it did. Certainly the switch from an A5000 to a RiscPC was a lot less painful than moving from RISC OS 2 to RISC OS 3 (this latter case not at all being helped by a widely used speed tweak - OS_UpdateMEMC,64,64 freezing a RISC OS 3 machine - helpful, guys!).
Elsewhere, the RiscPC was not as good a leap forward as it could have been due to an I/O world running at 8MHz (for podule compatibility? or just because?) plus a memory bus running at a rather slow 16MHz. This means that for all the super-fast IDE/SCSI hardware turning up in the epoch, the machine would - flat out - manage around 6.5MB/s. Thank God for the cache in the CPU, the original ARM610 (30MHz) was almost twice as fast as its memory; the 40MHz ARM710 faster yet. But while ARM was planning on releasing an ARM8 clocking around 60-70MHz, Digital knocked on the door and said "this thing? we call it a StrongARM. try two hundred megs.". And, lo and behold, a StrongARM card was made for the RiscPC that blew people's minds. Because, even with a crappy 16MHz bus, a 200+ processor with a large split cache was a hell of a step up from a 40MHz processor. But, as could have been predicted, the slow memory bus began to be an issue. So one enterprising company made a processor card with its own onboard memory that, for the most part, bypassed the motherboard's and... well... whoo-eee.

There is no such thing as a future-proof design. We hear it every so often and, with the benefit of hindsight, laugh in the faces of the people who promoted such silly concepts. However, given that the RiscPC is two decades old and many of the Acornites who bought a machine back then are still using them today, and given that it had so many possibilities and options all on the same motherboard... it was a pretty good attempt at a future-proof machine. Just to give you an idea, RISC OS Open are selling ROMs which contain a version of RISC OS 5 that will run on a RiscPC. This isn't without issue (it is a 32 bit world, just like the later devices), but it just goes to show you - the RiscPC is Acorn's enduring machine. Helped by an efficient ARM and a lightweight yet capable OS, it can still get work done with resources that are about on par with the average digital TV box. Now show me a build of anything other 'proper' operating system that is as happy on a twenty year old machine as a modern one. :-)

Well, hey, Happy Birthday RiscPC.

(damn, I feel old!)


No fancy pictures - I've been coding something all evening. If this sounds a bit rushed or has typos... yeah... I meant to write it several hours ago but was on a roll. You know, how you get your head into the code and... wait, if I say any more it'll sound like a cross between William Gibson and...uh...just bats**t insane. [nothing new there, then]


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