Re: Thermal considerations?
I like the way you think--but the designers are WAY ahead of you. For instance, Apple laptops would sleep between keystrokes--in 2000. I know that the AMD Athlon would power down the parts of the FPU not in use _every cycle_. That's not as big a deal as clock distribution, but I know I heard designers talking about powering down the clocks to the FPU when the fpu enable bit was not set.
Yes, crazy, really crazy, power saving measures became a thing near the death of bipolar (transistor) gates. The design teams saw no reason to ignore those lessons when MOSFET happened. Much has changed in the ten years since I moved on, but I am completely confident that they are only adding techniques when it comes to power savings.