ARM Evaluation System
An external second processor in a cheese wedge box containing an ARM 1 processor and 4Mb of RAM. It was the testbed of Acorn's new 32-bit RISC core, used by Acorn in the development of the Archimedes range of computers.
This is the rarest second processor ever produced.
A potted history
In the mid 1980s, Acorn had been developing the ABC line of workstations, each one a BBC Micro-derived computer attached by Tube to a more powerful second processor board. The range featured popular mid-level microprocessors of the day; among them the Z80, 68000, 80286 and 32016. Their goal in the ABC was partly to evaluate the new architectures, with a view to migrating their product line from the now limiting 6502. None of the contemporary offerings fulfilled their requirements, so the bold step was taken of commissioning a 32-bit RISC architecture in-house to meet Acorn's future needs. It was christened ARM, the Acorn RISC Machine.
While the instruction set was being developed, and emulated in BASIC on a BBC Micro with a 6502 Second Processor, fabrication of the ARM1 chip was done by VLSI, with whom Acorn had a contract for Uncommitted Logic Arrays (ULAs) in the BBC Micro series. Famously, the first samples worked perfectly. The processors were then fitted to their own second-processor board, the ARM Evaluation System, and distributed with development tools to encourage programmers to adopt the new architecture.
Due to subsequent events at Acorn, the ARM architecture was renamed the Advanced RISC Machine and spun off into another company, owned by ARM Holdings. Since then it has become a powerful force in the embedded systems market owing to its low power consumption, simplicity and high performance.
In 2006 the ARM came full circle and was designed into a new Tube platform, the ARM7TDMI Second Processor.