The Intel/Microsoft APM specification provides a system that allows
computers (especially laptops) to conserve electricity.

See About Advanced Power Management for background information.

The APM specification defines the following functions:
                Interface Connect Services                 needed?
INT 15H 5300H  Installation check                          No
INT 15H 5301H  Interface Connect                           No
INT 15H 5302H  Interface Connect (Protected Mode/16-bit)   No
INT 15H 5303H  Interface Connect (Protected Mode/32-bit)   No
INT 15H 5304H  Interface Disconnect                        Yes
                CPU Control Services                       
INT 15H 5305H  CPU Idle                                    Yes
INT 15H 5306H  CPU Busy                                    Yes
INT 15H 5307H  Set Power State                             Yes
                Status/Control Services                    
INT 15H 5308H  Enable/Disable APM Functionality            Yes
INT 15H 5309H  Restore APM BIOS Defaults                   No
INT 15H 530aH  Query Status                                No
                Power Management Event Notification        
INT 15H 530bH  Get Power Management Event                  Yes

See Also: About APM
INT 15H (AT Extended Services)
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Advance Power Management (APM) Functions