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 g

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.