Since more power consumption results in more failures and degradations in system performance, reliability, and power bills, it has been a critical problem for not only large scale server system but also personal computers (PCs). Though much literature has focused on energy management and power budgeting for server systems, power consumption of PCs does not attain sufficient attentions fairly. In this paper an online power measurement and prediction framework is proposed and used to save more energy considering the PC as a whole controlled system. The framework includes parts such as power measurement unit, power prediction unit and a simple execution unit of power reduction decisions. A hardware-software joint prototype is implemented based on an intelligent digital multimeter. Experiments on a desktop PC and a laptop show that PC with the framework can save more power consumptions than that of the PCs without this framework.