Why do CPUs run hotter...?

Why does a Pentium CPU run hotter when "working hard" (executing complex
software) than when the OS is idling?

It is always executing *some* instruction, and in that sense, is never idle.

I understand that CMOS gates dissipate power only when changing state. I
*presume* what's going on is that when the CPU is executing software, it is
executing a greater variety of machine instructions and therefore heating up
a larger proportion of the circuitry in the chip (since there is special
circuitry for each kind of instruction).

Am I on the right track? This is one of those dumb questions where I'd like
to know the exact answer, rather than just guessing.


.

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