ARM1


Acorn was now faced with a major problem; almost all its projects had been done on a 6502, so it
knew the hardware well. When seeking a new processor to replace the aging 6502, it found that
other processors just weren’t up to the job. Graphics systems were emerging, and it was clear
that the 6502 couldn’t keep up in the graphics fi eld. The Motorola 68000 was a 16/32-bit
microprocessor that was used in many family and business computers, but slow interrupt response
times meant that it couldn’t keep up with a communication protocol that the 6502 had no problem
running.. Numerous processors were studied and excluded. One by one, the processors on the
market were studied, analyzed, and rejected. Finally, the list ran out, and Acorn was left with no
choice; if it wanted to do things its way, it had to make its own processor.
Creating processors wasn’t necessarily something new; it was the golden age of multipurpose CPUs,
and several companies were designing CPUs, using little more than transparent fi lm and pens, but
what Acorn was about to do went well beyond simply designing a new CPU with 4000 transistors;
ARM set out to create a 32-bit processor.
The project was started in October 1983, with Sophie Wilson designing the instruction set and Steve
Furber doing the hardware design using BBC Micros to model and develop the chip, and on April
26, 1985, the fi rst Acorn RISC Machine processor was born, the ARM1. It also worked perfectly
the fi rst time, which was rather exceptional for a processor that was basically designed by hand.
The primary application of the ARM1 was to be a coprocessor on BBC Micros and to help create
the ARM2. Subsequent chips were sold as specialized coprocessors, or as development boards
linked onto BBC Masters. It was in 1987 when the first ARM-based computer was sold, the Acorn
Archimedes.