Software controlled power management

Reducing power consumption is critical in many system designs. Dynamic power management is an effective approach to decrease power without significantly degrading performance. Power management decisions can be implemented in either hardware or software. A recent trend on personal computers is to use software to change hardware power states. This paper presents a software architecture that allows system designers to investigate power management algorithms in a systematic fashion through a template. The architecture exploits the Advanced Configuration and Power Interface (ACPI), a standard for hardware and software. We implement two algorithms for controlling the power states of a hard disk on a personal computer running Microsoft Windows. By measuring the current feeding the hard disk, we show that the algorithms can save up to 25% more energy than the Windows power manager. Our work has two major contributions: a template for software-controlled power management and experimental comparisons of management algorithms for a hard disk.