Despite being relatively small compared to their industry peers, Acorn Computers were an innovative team. From their headquarters in Cambridge, they had already released the Atom, before following up in 1982 with their hugely successful Proton, otherwise known as the BBC Microcomputer. They had also branched out into new markets with the ABC, or Acorn Business Computer.
The ABC was not an astounding success, and certainly didn't meet the company's expectations. Nor did the Acorn Electron - a stripped-down BBC Micro intended for home use. While demand for the Electron was high, difficulties in producing the custom microchips used in its design meant few were sold - and, once stocks had risen to satisfactory levels, demand had long peaked.
One of the great strengths of the BBC Micro was the Tube, another Acorn development. The Tube was a fast bus that allowed for many different second processors to be installed, such as a Z80 or 80186. This allowed the BBC Micro to run different OSes, such as CP/M. Much of Acorn's development at this stage was focused on running more and better hardware off the Tube, but Acorn had seen the need for a powerful new solution if they were to succeed in the market from as early as the launch of the Atom in 1980.
The venerable 6502, upon which the Proton was based, was by 1983 quite long in the tooth. Acorn wanted a powerful, flexible new computer system, complete with a graphical user interface such as those Xerox had been experimenting with. Having asked Intel for 80186s to use, they had been turned away - and the 68000 was underwhelming.
The breakthrough came when Acorn engineers read the Berkeley RISC documents. The decision was swiftly made: if off-the-shelf processors don't make the grade, roll your own. Sophie Wilson, Acorn's virtuoso engineer, set to work, writing the processor's instruction set on a twin-6502 Beeb.
After the company was bought by Olivetti, full-scale efforts towards producing the new RISC processor - dubbed the Acorn RISC Machine, or ARM - were launched. VLSI Technology, a firm Acorn already contracted to produce various chips, such as ROMs, were asked to produce an ARM. On 26 April, 1985, the processor was delivered to Acorn - and, perhaps an omen of future success, it worked first time. The ARM1 was ready.
Using the ARM1 via the Tube as a co-processor in BBC Micros, the ARM2 was swiftly designed. The ARM2 was a 32-bit microprocessor, with 32-bit bus and 26-bit address space. The ARM2 was also Tube-compatible, and so it was decided that it should be implemented in development machines for the new Acorn computer: the Archimedes. The ARM2 was a top-secret project still at Acorn: even when courting Olivetti, they hadn't let on that it was under development.
The ARM Development System was released in 1986, at £4,000. A Tube-compatible co-processor for the BBC Master, it boasted an ARM2 which ran rings around the 286. It also came with three support chips, and 4MB of RAM. Acorn continued development of the Archimedes; now their wünderkind was ready, in the shape of the ARM, they needed the OS to run on it. This task was given to the Acorn Research Centre, or ARC, at Palo Alto, California.
Work on the OS, known as ARX, was slow. Acorn's goal of a UNIX-like OS would have had a truly modern platform, capable of pre-emptive multi-tasking, multi-threading, and multiple users. However, by 1987 it was clear that ARX would not be ready in time. A stop-gap was sought.
Hurridly, using the legendary BBC Basic which Sophie Wilson had ported to the ARM (which led to truly fast execution times), an OS was written, complete with GUI. With a gaudy, bright colour scheme reminiscent of early Commodore Amiga Workbench screens or Windows 2, it nonetheless got the job done. It featured an icon bar, displaying devices and applications, and windows for each currently-running application. Its name: ARTHUR, commonly believed to stand for "A RISC OS before THURsday".
Now Acorn had their hardware and software ready. In June, 1987, their ARM-based computer was launched: the Acorn Archimedes. The Archimedes, or Archie as they were affectionately known as (or, more often, simply Arc), came in four models to begin with, all equipped with an ARM2. The A305, with only 512k RAM and two expansion slots, was complimented by the A310 with a full megabyte. At the upper end, the A410 boasted 1MB RAM but four slots, whilst the top-of-the-line A420 boasted not only four slots and 2MB RAM, but a whopping 20MB hard disk. All four shipped with ARTHUR in ROM. Later, the A440 and A540 were released, with 4MB RAM and a 40MB hard drive, and 4MB and a 100MB hard drive, respectively.
The Archimedes was a desktop system, with the actual computer designed to sit on a desk, the monitor atop that. A keyboard plugged into this, and into that a three-buttoned mouse. The OS, to allow it to run on all systems (and not just those with hard drives), was burned onto ROMs. This allowed for swift boot times and operation, but was more difficult to upgrade. Nevertheless, Acorn began work on a proper, much less buggy OS for the Archimedes. The result of this was the RISC OS.
Originally to be named Arthur 2, this idea was scrapped when a film with a similar name was released. RISC OS 2 saw release in 1989, available on a set of ROMs to replace the original ARTHUR. RISC OS is a fast and easy-to-use OS, which featured many ideas ahead of their time. All applications are provided as folders, which carry all their resources. Double-clicking one in the Filer will run the app, whilst holding Shift when double-clicking will open the app's folder. All fonts are antialiased - a miracle in 1989. A command line could be accessed at any time just by tapping F12.
To go with the new OS, new hardware was designed, leading to the launch of the A3000. Still sporting the BBC branding, the Acorn Archimedes A3000 was an all-in-one unit like the Atari ST - floppy drive, computer and keyboard in one unit. The A3000 was an astounding success, with a powerful 8Mhz ARM2 and 1MB RAM, and sold well to both home and educational markets. The A3xx series was phased out.
ARM development hadn't stalled while Acorn worked on RISC OS - instead, they had produced a third iteration of the hardware. The ARM3 was a fast 25Mhz processor, and was used initially in the high-end A540. A new desktop machine, the A5000, soon saw launch, with an ARM3 to power it. This was again a traditional desktop case, and offered 4MB of RAM and a 40/80MB hard drive. Complimenting this was another version of RISC OS - RISC OS 3.0.
By now, Acorn had established dominance in the educational market. At home, they maintained a small, if reasonable marketshare - at least in the Commonwealth. Acorn weren't resting on their laurels, however, and decided in 1991 to continue to evolve their product lines. The A3000, with its ageing ARM2, was axed, replaced by two new derivitives: the A3010 (aimed towards home use, with a video port to connect to a TV set and a joystick port) and the A3020 (intended for educational use). The ARM2 was swapped for the ARM250 (literally ARM 2 and a half), which boasted higher clock speeds, and integrated some of the custom circuitry of the A3000.
The A5000 was joined by the A4000, a lower-profile machine. RISC OS 3.1 was now standard on all machines, the last major revision of the OS until the release of the Risc PC in 1994. Acorn's Archimedes line served them well for the late-80's and early 90's, powerful machines with a wonderful OS. However, Acorn's terrible efforts at marketing prevented them from gaining much acceptance outside of education, which would prove to be their downfall.