Last time I asked around about this question, the answer was surprisingly “probably not much”! When a low-power x86 chip (like those mobile chips) is idling (which is pretty much all the time if all you are doing is hosting a server on it) it consumes very little power, about the same level as an idling Pi. It is when the frequency ramps up that performance-per-watt gets noticeably worse on x86.
Edit: My personal test showed that my x86 laptop fared slightly worse than my Pi 3 in idling power (~2 watts higher it seems), but that laptop is oooooooold.
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At that point you’re running some sort of server on it probably.
For which, it’s not even the most cost effective hardware tbh. There are X86 based tiny PCs for good prices used
How does power consumption of those x86 PCs compare?
Last time I asked around about this question, the answer was surprisingly “probably not much”! When a low-power x86 chip (like those mobile chips) is idling (which is pretty much all the time if all you are doing is hosting a server on it) it consumes very little power, about the same level as an idling Pi. It is when the frequency ramps up that performance-per-watt gets noticeably worse on x86.
Edit: My personal test showed that my x86 laptop fared slightly worse than my Pi 3 in idling power (~2 watts higher it seems), but that laptop is oooooooold.