Modeling power management for hard disks

Recently, a large effort has been made to reduce the power consumed by computer-systems. Multiple power states have been defined, and mechanisms have been developed to allow system software to control transitions between these states. Unfortunately, little work has been done to determine effective times to change states. Statistical models of the power utilized by individual subsystems call provide a basis for making such decisions. The hard disk state model described provides both the quantitative data and insight necessary to design an efficient power management system.<>