What is Advanced Power Management (APM)?

Advanced Power Management (APM): Here, we are going to learn about the advanced power management, its history, power management events, power states, etc.
Submitted by Anushree Goswami, on January 09, 2021

APM: Advanced Power Management

APM is an abbreviation of "Advanced Power Management". It is an API designed and created by Intel and Microsoft. In 1992, it is launched. It allows an operating system functioning an IBM-compatible personal computer to keep up the job with the BIOS, a component of the firmware of computer, to accomplish power management.

  • Revision 1.2, which launched in 1996, was the last version of the APM design. ACPI is planned and projected as the descendant of APM.
  • APM makes use of a layered method to administer and control devices.
    APM-aware applications, which comprise device drivers, converse to an OS-specific APM driver. This driver makes a communication to the APM-aware BIOS, which manages and organizes the hardware. There is the potential to choose out of APM control on a device-by-device foundation, which can be used if a driver yearns to make a communication straightforwardly with a hardware device.

Power Management Events

There are overall 12 power management events, in addition OEM-defined events, that can be directed from the APM BIOS to the operating system.

The APM driver on a standard basis polls for event alteration notifications.

Power Management Events:

Name Code
System Standby Request Notification0x0001
System Suspend Request Notification0x0002
Normal Resume System Notification0x0003
Critical Resume System Notification0x0004
Battery Low Notification0x0005
Power Status Change Notification0x0006
Update Time Notification0x0007
Critical System Suspend Notification0x0008
User System Standby Request Notification0x0009
User System Suspend Request Notification0x000A
System Standby Resume Notification0x000B
Capabilities Change Notification0x000C

Power management functions:

Name Code
APM Installation Check0x00
APM Real Mode Interface Connect0x01
APM Protected Mode 16-bit Interface Connect0x02
APM Protected Mode 32-bit Interface Connect0x03
APM Interface Disconnect0x04
CPU Idle0x05
CPU Busy0x06
Set Power State0x07
Enable/Disable Power Management0x08
Restore APM BIOS Power-On Defaults0x09
Get Power Status0x0A
Get PM Event0x0B
Get Power State0x0C
Enable/Disable Device Power Management0x0D
APM Driver Version0x0E
Engage/Disengage Power Management0x0F
Get Capabilities0x10
Get/Set/Disable Resume Timer0x11
Enable/Disable Resume on Ring Indicator0x12
Enable/Disable Timer Based Requests0x13
OEM APM Installation Check0x80
OEM APM Function0x80

Power States

The APM design power states comprises system power states and device power states:

System power states

  • System Full On
  • APM Enabled
  • APM Standby
  • APM Suspend
  • System Off

Device power states

  • Device On
  • Device Power Managed
  • Device Low Power
  • Device Off

Reference: Advanced Power Management

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