I'm not an expert, but I think the high-power modes do things like very aggressive caching and branch prediction, etc. to speed things up. So there's a bunch o

I'm not an expert, but I think the high-power modes do things like very aggressive caching and branch prediction, etc. to speed things up. So there's a bunch of energy spent on e.g. transferring and storing memory that may never be used, or computing branches that may never be hit. Lower power modes don't do this as aggressively, so they only consume energy for results that will be used. Plus I'm pretty sure your base voltage has to be higher to run at higher frequency, and non linearly so, to counter various electrostatic effects.