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Home TECH 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 on top of the world. Unfortunately, trouble was just around the corner.

The small UK company became famous for winning a contract with the British Broadcasting Corporation to produce a computer for a national television show. Sales of his BBC Micro skyrocketed and were on track to exceed 1.2 million units.

A magazine advertisement for BBC Micro.  the slogan what
Enlarge / A magazine advertisement for BBC Micro. The tagline was “The Shape of Things to Come”.

But the world of personal computers was changing. The market for cheap 8-bit mics that parents would buy help the children with their homework it was getting saturated. And new machines from across the pond, like the IBM PC and the upcoming Apple Macintosh, promised significantly more power and ease of use. Acorn needed a way to compete, but didn’t have a lot of money for research and development.

A seed of an idea

Sophie Wilson, one of the BBC Micro designers, had anticipated this problem. She had added a slot called “Tube” that could connect to a more powerful central processing unit. A slotted CPU could take over the computer, leaving its original 6502 chip free for other tasks.

But which processor should you choose? Wilson and co-designer Steve Furber considered various 16-bit options, including the Intel 80286, National Semiconductor 32016, and Motorola 68000. But none were completely 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 Computer History Museum, Wilson explained, “We were able to see what all these processors did and what they didn’t do. So the first thing they didn’t do was they didn’t make good use of system memory, the second thing they didn’t do was they weren’t fast; they were not easy to use. We were used to programming the 6502 in machine code, and we were hoping that we could get to a level of power such that if you wrote in a higher level language you could achieve the same kinds of results.”

But what was the alternative? Was it even conceivable that little Acorn would make her own CPU from scratch? To find out, Wilson and Furber traveled to the National Semiconductor factory in Israel. They saw hundreds of engineers and a lot of expensive equipment. This confirmed their suspicions that such a task might be beyond them.

They then visited the Western Design Center in Mesa, Arizona. This company was building the beloved 6502 and designing a 16-bit successor, the 65C618. Wilson and Furber found little more than a “suburban bungalow” with some engineers and some students making diagrams using 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 making your own CPU seem possible. Wilson and Furber’s small team had built custom chips before, such as graphics and input/output chips for the BBC Micro. But those 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 had a Ph.D. in Physics, he gave the team 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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