Suppose you are building a device that needs a small CPU, it's running on battery power so you want to minimize the energy consumption, and you only need a small amount of computation. What's the most energy-efficient CPU?
My first thought would be that an 8-bit CPU would use the least energy. But on thinking about it further, maybe something a bit more powerful would be more efficient. For example, a 6502 has only a few thousand transistors, an ARM-1 has an order of magnitude more - but the ARM-1 delivers more than an order of magnitude more computing power, so it might overall save energy. Is that reasoning correct?