Joel Hruska, ExtremeTech, What does a CPU do when it’s doing nothing? here. It runs Java, that is my final answer.
Your CPU spends the vast majority of its time doing absolutely nothing. This is a fact that most tech enthusiasts are generally aware of, but the mechanics of how a CPU does nothing, switches over to briefly do something, and then returns to doing nothing again isn’t something we’ve discussed in great detail. It’s a question that’s increasingly important to modern processors; the goal of most chips built today is to return to their lowest power states as quickly as possible.