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I've been using a Bitcoin miner as a heater in the winter. I figure if I'm going to use resistive heat, I might as well generated some possibly-valuable wooden nickels as a side effect of the conversion from electrical to heat energy.

But I'm curious: does all the energy get turned into heat during computation? In practice, I understand that not all the energy gets truly applied to the computation in the first place, due to power supply inefficiencies and fans and if there are any spinning platters. And also, a little bit of energy leaves the system through LED indicators, EMI radiation, and along network cables, etc.

But does any of the energy actually get "consumed" in the computation itself, turned into information or something? From a thermodynamic perspective, is there any difference between a chip that draws 5W while quietly calculating digits of π inside, versus a length of nichrome wire drawing 5W? Do you get exactly 5W of heat out in both cases?

There's a related question at Is it necessary to consume energy to perform computation?, but I'm sort of asking the opposite: when energy is consumed performing (purely) computation, does every last bit of it end up as heat?

Community
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natevw
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2 Answers2

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The short answer is yes, computation does create heat by necessity. That is because the value in a register is often erased and replaced by some new value, and the loss of information (the loss of the old value that was stored) is intrinsically a contribution to entropy. This applies to any irreversible process, like storing a computed number, but NOT to reversible processes, like forming the exclusive-or of a number and a registered value. The exclusive-or of the same number a second time, with the register, will reverse the operation (yield the same result as before the first exclusive-or, i.e. that operation was not irreversible).

The more subtle inquiry, 'does every last bit of it end up as heat', is probably deserving of a 'no' answer. That is because the machine state (the ones and zeros held in memory) includes stored energy (charge variations on internal capacitances), so that with all common electronic technologies, there is nonthermal energy in the computation, produced as well as consumed. The program state of flash chips, for instance, is a kind of charged battery with many years required before that energy finally dissipates and turns into heat.

Whit3rd
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The answer to this question is a clear "yes", all of the power going into a computing device ultimately turns into heat*. There is no energy equivalent of information. Put another way, energetically speaking information is completely worthless.

*Well, unless you do something fancy such as running a thermodynamic cycle fed by the heat emitted from a processor, say, which could then convert a part of that heat into mechanical work or other forms of energy.

Pirx
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