This chapter provides an overview of the various power management technologies in Linux. The configuration of all available APM (advanced power management), ACPI (advanced configuration and power interface), and CPU frequency scaling settings are described in detail.
Unlike APM, which was previously used on laptops for power management only, the hardware information and configuration tool ACPI is available on all modern computers (laptops, desktops, and servers). On many types of modern hardware, the CPU frequency can be adapted to the situation, which helps save valuable battery time especially on mobile devices (CPU frequency scaling).
All power management technologies require suitable hardware and BIOS routines. Most laptops and many modern desktops and servers meet these requirements. APM had been used in many older computers. As APM largely consists of a function set implemented in the BIOS, the level of APM support may vary depending on the hardware. This is even more true of ACPI, which is even more complex. For this reason, it is virtually impossible to recommend one over the other. Simply test the various procedures on your hardware then select the technology that is best supported.