April 25th, 2016

Hard Stare

Acorn: from niche to forgotten obscurity and total industry dominance at the same time

More retrocomputing meanderings -- whatever became of the ST, Amiga and Acorn operating systems?

The Atari ST's GEM desktop also ran on MS-DOS, DR's own DOS+ (a forerunner of the later DR-DOS) and today is included with FreeDOS. In fact the first time I installed FreeDOS I was *very* surprised to find my name in the credits. I debugged some batch files used in installing the GEM component.

The ST's GEM was the same environment. ST GEM was derived from GEM 1; PC GEM from GEM 2, crippled after an Apple lawsuit. Then they diverged. FreeGEM attempted to merge them again.

But the ST's branch prospered, before the rise of the PC killed off all the alternative platforms. Actual STs can be quite cheap now, or you can even buy a modern clone:

http://harbaum.org/till/mist/index.shtml

If you don't want to lash out but have a PC, the Aranym environment gives you something of the feel of the later versions. It's not exactly an emulator, more a sort of compatibility environment that enhances the "emulated" machine as much as it can using modern PC hardware.

http://aranym.org/

And the ST GEM OS was so modular, different 3rd parties cloned every components, separately. Some commercially, some as FOSS. The Aranym team basically put together a sort of "distribution" of as many FOSS components as they could, to assemble a nearly-complete OS, then wrote the few remaining bits to glue it together into a functional whole.

So, finally, after the death of the ST and its clones, there was an all-FOSS OS for it. It's pretty good, too. It's called AFROS, Atari Free OS, and it's included as part of Aranym.

I longed to see a merger of FreeGEM and Aranym, but it was never to be.

The history of GEM and TOS is complex.

Official Atari TOS+GEM evolved into TOS 4, which included the FOSS Mint multitasking later, which isn't much like the original ROM version of the first STs.

The underlying TOS OS is not quite like anything else.

AIUI, CP/M-68K was a real, if rarely-seen, OS.

However, it proved inadequate to support GEM, so it was discarded. A new kernel was written using some of the tech from what was later to become DR-DOS on the PC -- something less like CP/M and more like MS-DOS: directories, separated with backslashes; FAT format disks; multiple executable types, 8.3 filenames, all that stuff.

None of the command-line elements of CP/M or any DR DOS-like OS were retained -- the kernel booted the GUI directly and there was no command line, like on the Mac.

This is called GEMDOS and AIUI it inherits from both the CP/M-68K heritage and from DR's x86 DOS-compatible OSes.

The PC version of GEM also ran on Acorn's BBC Master 512 which had an Intel 80186 coprocessor. It was a very clever machine, in a limited way.

Acorn's series of machines are not well-known in the US, AFAICT, and that's a shame. They were technically interesting, more so IMHO than the Apple II and III, TRS-80 series etc.

The original Acorns were 6502-based, but with good graphics and sound, a plethora of ports, a clear separation between OS, BASIC and add-on ROMs such as the various DOSes, etc. The BASIC was, I'd argue strongly, *the* best 8-bit BASIC ever: named procedures, local variables, recursion, inline assembler, etc. Also the fastest BASIC interpreter ever, and quicker than some compiled BASICs.

Acorn built for quality, not price; the machines were aimed at the educational market, which wasn't so price-sensitive, a model that NeXT emulated. Home users were welcome to buy them & there was one (unsuccessful) home model, but they were unashamedly expensive and thus uncompromised.

The only conceptual compromise in the original BBC Micro was that there was provision for ROM bank switching, but not RAM. The 64kB memory map was 50:50 split ROM and RAM. You could switch ROMs, or put RAM in their place, but not have more than 64kB. This meant that the high-end machine had only 32kB RAM, and high-res graphics modes could take 21kB or so, leaving little space for code -- unless it was in ROM, of course.

The later BBC+ and BBC Master series fixed that. They also allowed ROM cartridges, rather than bare chips inserted in sockets on the main board, and a numeric keypad.

Acorn looked at the 16-bit machines in the mid-80s, mostly powered by Motorola 68000s of course, and decided they weren't good enough and that the tiny UK company could do better. So it did.

But in the meantime, it kept the 6502-based, resolutely-8-bit BBC Micro line alive with updates and new models, including ROM-based terminals and machines with a range of built-in coprocessors: faster 6502-family chips for power users, Z80s for CP/M, Intel's 80186 for kinda-sorta PC compatibility, the NatSemi 32016 with PANOS for ill-defined scientific computing, and finally, an ARM copro before the new ARM-based machines were ready.

Acorn designed the ARM RISC chip in-house, then launched its own range of ARM-powered machines, with an OS based on the 6502 range's. Although limited, this OS is still around today and can be run natively on a Raspberry Pi:

https://www.riscosopen.org/content/

It's very idiosyncratic -- both the filesystem, the command line and the default editor are totally unlike anything else. The file-listing command is CAT, the directory separator is a full stop (i.e. a period), while the root directory is called $. The editor is a very odd dual-cursor thing. It's fascinating, totally unrelated to the entire DEC/MS-DOS family and to the entire Unix family. There is literally and exactly nothing else even slightly like it.

It was the first GUI OS to implement features that are now universal across GUIs: anti-aliased font rendering, full-window dragging and resizing (as opposed to an outline), and significantly, the first graphical desktop to implement a taskbar, before NeXTstep and long before Windows 95.

It supports USB, can access the Internet and WWW. There are free clients for chat, email, FTP, the WWW etc. and a modest range of free productivity tools, although most things are commercial.

But there's no proper inter-process memory protection, GUI multitasking is cooperative, and consequently it's not amazingly stable in use. It does support pre-emptive multitasking, but via the text editor, bizarrely enough, and only of text-mode apps. There was also a pre-emptive multitasking version of the desktop, but it wasn't very compatible, didn't catch on and is not included in current versions.

But saying all that, it's very interesting, influential, shared-source, entirely usable today, and it runs superbly on the £25 Raspberry Pi, so there is little excuse not to try it. There's also a FOSS emulator which can run the modern freeware version:

http://www.marutan.net/rpcemu/

For users of the old hardware, there's a much more polished commercial emulator for Windows and Mac which has its own, proprietary fork of the OS:

http://www.virtualacorn.co.uk/index2.htm

There's an interesting parallel with the Amiga. Both Acorn and Commodore had ambitious plans for a modern multitasking OS which they both referred to as Unix-like. In both cases, the project didn't deliver and the ground-breaking, industry-redefiningly capable hardware was instead shipped with much less ambitious OSes, both of which nonetheless were widely-loved and both of which still survive in the form of multiple, actively-maintained forks, today, 30 years later -- even though Unix in fact caught up and long surpassed these 1980s oddballs.

AmigaOS, based in part on the academic research OS Tripos, has 3 modern forks: the FOSS AROS, on x86, and the proprietary MorphOS and AmigaOS 4 on PowerPC.

Acorn RISC OS, based in part on Acorn MOS for the 8-bit BBC Micro, has 2 contemporary forks: RISC OS 5, owned by Castle Technology but developed by RISC OS Open, shared source rather than FOSS, running on Raspberry Pi, BeagleBoard and some other ARM boards, plus some old hardware and RPC Emu; and RISC OS 4, now owned by the company behind VirtualAcorn, run by an ARM engineer who apparently made good money selling software ARM emulators for x86 to ARM holdings.

Commodore and the Amiga are both long dead and gone, but the name periodically changes hands and reappears on various bits of modern hardware.

Acorn is also long dead, but its scion ARM Holdings designs the world's most popular series of CPUs, totally dominates the handheld sector, and outsells Intel, AMD & all other x86 vendors put together something like tenfold.

Funny how things turn out.