The USB chip (like many microcontrollers) has clock gating and sleep modes so it uses almost no power when idle. When running it uses 10 mA (50 mW) which is pre

The USB chip (like many microcontrollers) has clock gating and sleep modes so it uses almost no power when idle. When running it uses 10 mA (50 mW) which is pretty low, but in deep sleep mode it uses just 100 µA (0.5 mW). In comparison, a desktop processor can use 95 W or more and the Cray 1 used over 100 kW.