5 ms·

The author states "For every watt of power the CPU consumes, it must dissipate a watt of heat." It was always my understanding that that in electrical devices,

The author states "For every watt of power the CPU consumes, it must dissipate a watt of heat." It was always my understanding that that in electrical devices, (with the exception of heaters) the amount of heat produced was inversely proportional to the efficiency of the device. So is it really true that all energy provided to the CPU or SOC is dissapated as heat?

Elrac 8y ago
The author's sentence is essentially a truism, because fiddling with information _as such_ and in theory doesn't use up any energy. As practically implemented in current CPU electronics, though, information needs to be communicated from point A to point B as a change in voltage. To convey that voltage change means having to move some amount of electrical charge into or out of the tiny capacitor that is a transistor's gate, via the non-perfect conductor that is the doped-silicon trace between the two points. Resistance saps part of the energy moving those electrons around and converts it to heat.
- dnautics 8y ago
  > fiddling with information _as such_ and in theory doesn't use up any energy. that's not true at all. Any time you destroy information (for example an and gate can destroy information) you use energy.
  - Elrac 8y ago
    Chances are you know more about this than I do, and I'd be interested to learn more. If you're willing to explain, I wonder how an AND gate destroys information. Certainly the output of a 2-input AND gate carries less information than both inputs together. But unless the gate is destroying the input signals, which it isn't, I don't see how infomation is being destroyed.
    - dnautics 8y ago
      https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle
jamesough 8y ago
Yep, it all ends up as heat. Energy is conserved, so if it didn't end up as heat, it would have to go somewhere, and there isn't really anywhere else it could go. Related topic: reversible computing. You might wonder if a computation need take any energy at all: it turns out that an irreversible computation (e.g. NOR, XOR, AND etc) is physically guaranteed to waste energy, but if you make sure your compute steps are always reversible (i.e. each input maps to one and only one output) then you can theoretically compute for free (the Feynmann lectures on computation cover this well). But these energies are negligible compared to the wattage that goes through a standard CPU.
cgdcraig 8y ago
That's true only of devices that don't convert the energy into work(motors), light(LEDs) or other voltages(transformers). All other electronics convert all the power into heat. Basically any computer is a heater that so happens is able to do math as well. Energy is consumed for doing a computation but it's 6-7 orders smaller than what the heat produced

Elrac 8y ago

The author's sentence is essentially a truism, because fiddling with information _as such_ and in theory doesn't use up any energy. As practically implemented in current CPU electronics, though, information needs to be communicated from point A to point B as a change in voltage. To convey that voltage change means having to move some amount of electrical charge into or out of the tiny capacitor that is a transistor's gate, via the non-perfect conductor that is the doped-silicon trace between the two points. Resistance saps part of the energy moving those electrons around and converts it to heat.

dnautics 8y ago
> fiddling with information _as such_ and in theory doesn't use up any energy. that's not true at all. Any time you destroy information (for example an and gate can destroy information) you use energy.
- Elrac 8y ago
  Chances are you know more about this than I do, and I'd be interested to learn more. If you're willing to explain, I wonder how an AND gate destroys information. Certainly the output of a 2-input AND gate carries less information than both inputs together. But unless the gate is destroying the input signals, which it isn't, I don't see how infomation is being destroyed.
  - dnautics 8y ago
    https://en.wikipedia.org/wiki/Landauer%27s_principle https://en.wikipedia.org/wiki/Landauer%27s_principle

jamesough 8y ago

Yep, it all ends up as heat. Energy is conserved, so if it didn't end up as heat, it would have to go somewhere, and there isn't really anywhere else it could go. Related topic: reversible computing. You might wonder if a computation need take any energy at all: it turns out that an irreversible computation (e.g. NOR, XOR, AND etc) is physically guaranteed to waste energy, but if you make sure your compute steps are always reversible (i.e. each input maps to one and only one output) then you can theoretically compute for free (the Feynmann lectures on computation cover this well). But these energies are negligible compared to the wattage that goes through a standard CPU.

cgdcraig 8y ago

That's true only of devices that don't convert the energy into work(motors), light(LEDs) or other voltages(transformers). All other electronics convert all the power into heat. Basically any computer is a heater that so happens is able to do math as well. Energy is consumed for doing a computation but it's 6-7 orders smaller than what the heat produced