There is a clear trade-off between saving energy and system performance and their respective priorities vary according to time and circumstances. To solve this problem, it will be necessary to add another function to change the management policy in each condition. This technique effectively lowers CPU power, but the ratio of CPU power to the total system power is almost always less than 40% [ 17]. Unfortunately, other components such as memories and disk drives do not have a wide dynamic power range like CPUs.