In broad strokes, what are the most energy costly parts of a computation? One must be particularly bad... I'm guessing CPU activity, because it generates the mo

In broad strokes, what are the most energy costly parts of a computation? One must be particularly bad... I'm guessing CPU activity, because it generates the most heat? If you broke it down further, what's the most expensive parts of it? What causes divergence between energy efficiency and time complexity? I would expect both roughly scale proportionate to the number of instructions executed.