History of ARM, Part 1: Building the first chip

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It was 1983, and Acorn Computers was on top of the world. Unfortunately, problems were around the corner.

The small British company is best known for winning a contract with the BBC to produce a computer for a national television programme. Its BBC Micro sales soared to over 1.2 million units.

An advertisement in BBC Micro magazine.  was the motto
Zoom / An advertisement in BBC Micro magazine. The motto was “the shape of things to come”.

But the world of personal computers was changing. The market for cheap 8-bit micros that parents buy to help kids with their homework is saturated. New devices from across the pond, such as the IBM PC and the upcoming Apple Macintosh, promised significantly more power and ease of use. Acorn needed a way to compete, but he didn’t have much money for research and development.

seed idea

Sophie Wilson, one of BBC Micro’s designers, foresaw this problem. It has added a slot called a “tube” that can connect to a more powerful CPU. A slotted CPU can take over the computer, leaving the original 6502 chip free from other tasks.

But which therapist should you choose? Wilson and co-designer Steve Furber considered several 16-bit options, such as Intel’s 80286, National Semiconductor’s 32016, and Motorola’s 68000. But none of it was entirely satisfactory.

CPUs 286, 32016, and 68000, approx at scale.
Zoom / CPUs 286, 32016, and 68000, approx at scale.

Wikipedia

In a later interview with the Museum of Computing History, Wilson explained, “We can see what all these processors did and didn’t do. So the first thing they didn’t do was they didn’t make good use of the memory system. The second thing they didn’t do was they weren’t fast.” It wasn’t easy to use. We used to program the 6502 into machine code, and we hoped we could get to the power level so that if you wrote in a higher level language, you could achieve the same kinds of results.”

But what is the alternative? Was it even possible for a small company Acorn to make their own CPU from scratch? To find out, Wilson and Furber took a trip to the National Semiconductor plant in Israel. They saw hundreds of engineers and a huge amount of expensive equipment. This confirmed their suspicion that such a task might be beyond them.

Then they visited the Western Design Center in Mesa, Arizona. This company was making the beloved 6502 and designing the 16-bit successor, the 65C618. Wilson and Furber found little more than a “suburban house” with a few engineers and some students drawing blueprints using old Apple II computers and bits of masking tape.

Western Design Center in 2022, according to Google.  It might even be the same as a bungalow!
Zoom / Western Design Center in 2022, according to Google. It might even be the same as a bungalow!

Suddenly, making their own CPU seemed like a possibility. Wilson and Furber’s small team have built custom chips before, such as graphics and I/O chips for the BBC Micro. But these designs were simpler and contained fewer CPU components.

Despite the challenges, Acorn’s senior management has supported their efforts. In fact, they’ve gone beyond just support. Hermann Hauser, co-founder of Acorn, Ph.D. In physics, the team gave copies of IBM research papers describing a new and more powerful type of CPU. It was called RISC, which stands for “Reduced Instruction Set Computing.”

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