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The ARM chip was low power essentially by accident. The designers wanted to keep it under (I think) 10 watts which would let them use cheap plastic packages for

by kens 6y ago

The ARM chip was low power essentially by accident. The designers wanted to keep it under (I think) 10 watts which would let them use cheap plastic packages for the chips. But they didn't have good power simulation tools so they needed to be very conservative with the design. When they manufactured the chips, they found the power consumption was closer to 1 watt. Edit: as beagle3 pointed out, I got the numbers wrong; they aimed for 1 watt and came in under 0.1 watt. For more details, see Steve Furber's oral history, page 15. He says "Effectively, we used Victorian engineering margins on the power consumption of the chip." https://archive.computerhistory.org/resources/access/text/2012/05/102746196-05-01-acc.pdf https://archive.computerhistory.org/resources/access/text/20...

beagle3 6y ago
May find it later when I am not on mobile, but iirc they aimed for 1W and ended up achieving 0.1W or so - at first they were sure something was wrong about their test rig because it seemed like an unpowered CPU was actually working - and then they realized that it was getting enough power through the data and address lines, even though the Vcc was not connected.
- js2 6y ago
  > The power test tools they were using were unreliable and approximate, but good enough to ensure this rule of thumb power requirement. When the first test chips came back from the lab on the 26 April 1985, Furber plugged one into a development board, and was happy to see it working perfectly first time. > Deeply puzzling, though, was the reading on the multimeter connected in series with the power supply. The needle was at zero: the processor seemed to be consuming no power whatsoever. > As Wilson tells it: “The development board plugged the chip into had a fault: there was no current being sent down the power supply lines at all. The processor was actually running on leakage from the logic circuits. So the low-power big thing that the ARM is most valued for today, the reason that it's on all your mobile phones, was a complete accident." > Wilson had, it turned out, designed a powerful 32-bit processor that consumed no more than a tenth of a Watt. https://www.theregister.com/2012/05/03/unsung_heroes_of_tech_arm_creators_sophie_wilson_and_steve_furber/ https://www.theregister.com/2012/05/03/unsung_heroes_of_tech...
  - macintux 6y ago
    An incredible story, thanks.
- JProthero 6y ago
  Here's a link to the video of an interview with Steve Furber [1], who worked on the chip's development, discussing this. [1] https://youtu.be/1jOJl8gRPyQ?t=508 https://youtu.be/1jOJl8gRPyQ?t=508

by kens 6y ago

beagle3 6y ago

May find it later when I am not on mobile, but iirc they aimed for 1W and ended up achieving 0.1W or so - at first they were sure something was wrong about their test rig because it seemed like an unpowered CPU was actually working - and then they realized that it was getting enough power through the data and address lines, even though the Vcc was not connected.

js2 6y ago
> The power test tools they were using were unreliable and approximate, but good enough to ensure this rule of thumb power requirement. When the first test chips came back from the lab on the 26 April 1985, Furber plugged one into a development board, and was happy to see it working perfectly first time. > Deeply puzzling, though, was the reading on the multimeter connected in series with the power supply. The needle was at zero: the processor seemed to be consuming no power whatsoever. > As Wilson tells it: “The development board plugged the chip into had a fault: there was no current being sent down the power supply lines at all. The processor was actually running on leakage from the logic circuits. So the low-power big thing that the ARM is most valued for today, the reason that it's on all your mobile phones, was a complete accident." > Wilson had, it turned out, designed a powerful 32-bit processor that consumed no more than a tenth of a Watt. https://www.theregister.com/2012/05/03/unsung_heroes_of_tech_arm_creators_sophie_wilson_and_steve_furber/ https://www.theregister.com/2012/05/03/unsung_heroes_of_tech...
- macintux 6y ago
  An incredible story, thanks.
JProthero 6y ago
Here's a link to the video of an interview with Steve Furber [1], who worked on the chip's development, discussing this. [1] https://youtu.be/1jOJl8gRPyQ?t=508 https://youtu.be/1jOJl8gRPyQ?t=508