The start of the revival - The ARM and the Archimedes (1986 to 1988).

Back in 1983, Acorn had asked Intel for a sample 80286 processor, and Intel had refused. As a direct result of this refusal, a team was set up within Acorn, under Roger Wilson and Steve Furbur, to try and develop a RISC (Reduced Instruction Set Chip) processor. Such was the secrecy surrounding this project that when Olivetti took a controlling share of Acorn in 1985 they were not told about the development team until after the negotiations had been finalised.

The first production version of the ARM chip, the ARM2 (the ARM1 was only used in development machines), was possibly the simplest RISC processor in the world, with only 30,000 transistors. The instruction set was devised by Roger Wilson. It featured a true 32-bit data bus, and a 26-bit address bus, with 16 registers and no on-chip cache. The first ARM-based product was the ARM Development System, a second processor for the BBC Master. It cost around £4,000 to buy, and included the ARM processor and three support chips, 4 Mb of RAM and a set of development tools with an enhanced version of BBC BASIC. The second ARM-based product was the Acorn Archimedes.

The Archimedes was released in mid-1987. There were initially four different models in the range, the A305 and A310, and the A410 (never really available) and A440. They all shared the same basic hardware - the ARM2 processor and the three support chips (MEMC, the memory controller, VIDC, the display and sound controller and IOC, the I/O controller). All machines also had mono and colour monitor outputs, a printer port, a 9-pin serial port and a headphone socket. There was also provision for a standard Econet interface to be fitted.

Further expansion was catered for by a two or four slot backplane, which accepted 16- or 32-bit expansion cards called podules (for "peripheral modules"). The main variations in the different models were the amount of memory, the disc support add the backplane. The base model, the A305, had 512 Kb of memory, expandable to 1 Mb, and the A310 had 1 Mb. Both these machines could only support floppy drives by default, although it was possibly to buy an add-on hard drive interface, and were not supplied with a backplane. Above this was the A410, also with 1 Mb of memory but with an ST506-based hard disc drive interface integrated with the motherboard and a four-slot backplane. Finally, the top of the range model, the A440, came with 4 Mb of memory, a 20 Mb ST506 hard disc drive and the four-slot backplane.

The original operating system was called Arthur. It came with an upgraded version of BBC BASIC, BBC BASIC V, containing many enhancements over BBC BASIC IV, a simple text editor, a paint package, Maestro (a music editor) and 65Host (a 6502 emulator that allowed most BBC Micro programs written in 6502 Assembler to be run on the Archimedes). When Arthur was originally released it contained a large number of bugs - one report at the time noted that an Archimedes had been seen sporting a sticker with a warning that the operating system could randomly delete files of its own accord. Acorn pumped money and resources in to developing and improving Arthur, and by the end of 1988 there had been at least three major releases.

When the Archimedes was launched, the A305 cost £800 to £1000, the A310 cost £950 to £1200 and the A440 cost £2900 to £3150, depending on the type of monitor supplied.

The Acorn revival was underway, but wasn't quite complete. The following year, 1989, would prove to be another turning point.

Next: Playing with UNIX - The R140 (1989).

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Robert McMordie

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