Breakfast in America
The place was a revelation. As Furber recalls: “We went there expecting big shiny American office buildings with lots of glass windows, fancy copy machines… And what we found was… a bungalow in the suburbs… Yeah, they’d got some big equipment, but they were basically doing this on Apple IIs.”
Mensch assumed that Wilson and Furber turned down the new version of the 6502 because they were looking for a full 32-bit processor to compete with Apple’s plans for the 16-bit Apple IIgs. Mensch didn’t want to be rushed into 32-bit until he’d completed the current 24-bit project.
Wilson and Furber in the mid-1980s
He says: “They didn't want to wait for me to start the 32-bit version so they left upset with my choice and decided that they could do the design themselves in Cambridge.”
What had decided them wasn’t being “upset” at Mensch’s reluctance. It was the encouragingly tiny scale of his globally successful operation. As Wilson tells it: “A couple of senior engineers, and a bunch of college kids… were designing this thing… We left that building utterly convinced that designing processors was simple.”
Simple? IBM’s own commercially unsuccessful first attempt at a Risc processor had taken months of instruction set simulation on heavy mainframes. Wilson, however, just plunged right in. Herman Hauser remembers: “Sophie did it all in her brain.”
It was Furber’s job to turn Wilson’s brainchild into something that could be taped out and sent off to the factory for fabrication. Once she’d thought out the instruction sets, “Steve then knocked things out”, she recalls.
“It turned out there is no magic," says Furber. "A microprocessor’s just a lump of logic, like everything else we'd designed. There are no formidable hurdles. The Risc idea was a good one, it made things much simpler. And 18 months later, after about 10 or 12 man years of work, we had a working ARM in our hands. Which probably surprised us as much as it surprised everybody else.”
Next page: Call to ARMs
Almost brought a tear to my eye. A beautiful article about a beautiful piece of technology. My jaw dropped when I read the ARM worked without applying Vcc :)
IBM ROMP vs. ARM
The IBM ROMP chip (aka the 801) was never intended to be a general purpose RISC processor. It was intended to power an office automation product (think of a hardware word-processor like WANG used to sell).
As a result, although it could function as a General Purpose CPU, it was not really that suited for it. It was never a success because at the time, IBM could not see justification for entering the pre-Open Systems UNIX world. RT 6150 and the 6151 were intended as niche systems mainly for education, although they did surface as channel attached display front ends for CADAM and CATIA run on mainframes (and could actually run at least CATIA themselves). This changed completely with the RIOS RISC System/6000 architecture, where IBM was determined to have a creditable product, and invested heavily.
In comparison, the ARM was designed from the ground up as a general purpose CPU. Roger Wilson (as he was then) greatly admired the simplicity and orthogonality of the 6502 instruction set (it is rather elegant IMHO), and designed the instruction set for the ARM in a similar manner. Because the instruction set was orthogonal (like the 6502, the PDP11, and the NS320XX family), it makes the instruction decoding almost trivial. It also made modelling the ARM on an econet of BBC micro's (in BBC Basic, no less) much easier, which allowed them to debug the instruction set before committing anything to silicon.
They had to make some concessions on what they wanted. There was no multiply-add instruction, which appeared to be a hot item in RISC design at the time, and to keep it simple and within the transistor budget, all they could do was a shift-add, (the barrel shifter), which although useful, was a barrier to ultimate performance, but great for multi-byte graphics operations.
It was also simple enough so that they could design the interface and the support chips (MEMC, VIDC and IOC) themselves, achieving early machines with low chip counts.
This is all from memory of articles in Acorn User, PC World, Byte and other publications. Feel free to correct me if my recollections are wrong.
This is why I come to the Reg, so much nicer to read a well informed structured article as opposed to the usual "my dads bigger than your dad" fanboy rantings on other sites
I would just like to congratulate the author of this article. Beautifully written. A real credit to yourself, and The Register, sir. Thank you very much.
It struck me that Hauser, despite not being the technical guy, is as bright as they come. He clearly recognised the talent he had with Wilson and Furber.
I completely riviting read. Actually, the story of Acorn & ARM would make a very good book. Ditto Inmos IMHO.
Have a good day all.
Re: Great article
I agree, it wasn't Acorn and the ARM which failed.
But there is something about the British industrial and financial environment which seems to let the winnings from these works of genius drift away out of reach.
Its not just globalisation, and some factory that is so expensive to build that there can only be one on the entire planet. And we can't expect to spot the right investment choice every time. But what is it about this country which turns a successful entrepreneur into somebody fronting a TV show that tests how people can run a market stall in Essex?