A history of ARM, part 1: Building the first chip


A History of ARM Part 1: Building the First Chip

Aurich Lawson/Getty Images

It was 1983 and Acorn Computers was at the top of the world. Unfortunately, trouble was just around the corner.

The small British company was famous for winning a contract with the British Broadcasting Corporation to manufacture a computer for a national television programme. Sales of the BBC Micro skyrocketed, topping 1.2 million units.

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A magazine advert for BBC Micro.  The slogan was
Enlarge / A magazine advert for BBC Micro. The slogan was “The Shape of Things to Come”.

But the world of PCs has changed. The market for cheap 8-bit mics, which parents would buy to help kids with their homework, was saturated. And new machines from across the pond, like the IBM PC and upcoming Apple Macintosh, promised significantly better performance and ease of use. Acorn needed a way to stay competitive, but it didn’t have much money for research and development.

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A seed of an idea

Sophie Wilson, one of the BBC Micro’s designers, foresaw this problem. She had added a slot called “Tube” that could be plugged into a more powerful CPU. A slotted CPU could take over the computer, leaving its original 6502 chip free for other tasks.

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But which processor should she choose? Wilson and co-designer Steve Furber evaluated various 16-bit options, such as Intel’s 80286, National Semiconductor’s 32016, and Motorola’s 68000. But none were entirely satisfactory.

The 286, 32016 and 68000 CPUs, roughly to scale.
Enlarge / The 286, 32016 and 68000 CPUs, roughly to scale.

Wikipedia

In a later interview with the Computing History Museum, Wilson explained, “We could see what all these processors were doing and what they weren’t doing. 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; They weren’t easy to use. We were used to programming the 6502 in machine code, and we rather hoped that we could achieve such a level of performance that writing in a high-level language could produce the same results.”

But what was the alternative? Was it even conceivable for tiny Acorn to build her own CPU from scratch? To find out, Wilson and Furber took a trip to the National Semiconductor factory in Israel. They saw hundreds of engineers and a huge amount of expensive equipment. This confirmed her suspicion that such a task could be beyond her.

They then visited the Western Design Center in Mesa, Arizona. This company made the popular 6502 and designed a 16-bit successor, the 65C618. Wilson and Furber found little more than a “suburb bungalow” with a few engineers and a few students making diagrams with old Apple II computers and pieces of duct tape.

The Western Design Center in 2022, according to Google.  It could even be the same bungalow!
Enlarge / The Western Design Center in 2022, according to Google. It could even be the same bungalow!

Suddenly it seemed possible to build your own CPU. Wilson and Furber’s small team had previously built custom chips, such as the graphics and I/O chips for the BBC Micro. But these designs were simpler and had fewer components than a CPU.

Despite the challenges, Acorn’s senior management supported their efforts. In fact, they went beyond mere support. Acorn co-founder Hermann Hauser, who holds a Ph.D. in physics, gave the team copies of IBM research papers describing a new and more powerful type of CPU. It was called RISC, which stood for Reduced Instruction Set Computing.



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