ACPI Programming Guide: Dynamic Power Management

As we have seen, hardware may provide a variety of mechanisms to manage power, including sleep modes and clock rate control. Methods that reconfigure system states to optimize power consumption are known as dynamic power management. These mechanisms are typically managed by the operating system, which provides a software interface to the system tasks. The operating system views its own power states as a resource to be managed along with other resources. Centralizing the control of the power management mechanisms in the operating system allows the OS to ensure that all necessary components are notified of any change to the power management state.