Power management control software including power management policies is provided with those policies divided into observation code 18, 20, 22 and response code 26, 28, 30. When predetermined execution points 10, 12 within the operating system 2 are reached registered observation code 18, 20 for those execution points 10, 12 is triggered to be executed and serves to store event data within an event data store 24. At another time independent of the execution points 10, 12, the response code 26, 28, 30 is executed to read the event data from the event data store 24 and generate power control predictions and control signals therefrom.