Frequently Asked Questions

Q: What is APM and ACPI?

A:

Advanced Power Management

The BIOS Setup Utility supports Advanced Power Management (APM) and standby mode. The energy-saving standby mode is initiated in the following ways:

  • Time-out period specified in the BIOS Setup Utility
  • Suspend/resume switch connected to the front panel sleep connector
  • From the operating system, such as the Suspend menu item in Windows® 95

    • In standby mode, the motherboard reduces power consumption by using SMM capabilities. Reducing power to or turning off Video Electronics Standards Association (VESA) Display Power Management Signaling (DPMS)-compliant monitors and spinning down hard disks are examples of this.
The BIOS enables APM by default, but the operating system must support an APM driver for the power-management features to work.

Advanced Configuration and Power Interface

Under Advanced Configuration and Power Interface (ACPI), the operating system directs all computer and device power state transitions. The operating system places devices in and out of low power states based on preference and knowledge of how devices are being used by programs. Devices not being used may be turned off, or the entire computer may be placed in a low-power state.

ACPI gives the operating system direct control over the power management and Plug and Play functions of a computer. ACPI requires an ACPI-aware operating system, such as Windows NT 4.0, Windows 98 SE, Windows 2000, and Windows Me.

ACPI features include:

  • Plug and Play (including bus and device enumeration) and Advanced Power Management (APM) functionality normally contained in the BIOS Setup Utility.
  • Power management control of individual devices, add-in boards (some add-in boards may require an ACPI-aware driver), video displays, and hard disk drives.
  • Methods for achieving less than 30-watt computer operation in the Power On Suspend sleeping state, and less than five-watt computer operation in the Suspend to Disk sleeping state.
  • A soft-off feature that enables the operating system to turn off the computer.
  • Support for multiple wake up events.
  • Support for a front panel power and sleep mode switch.

How is APM Different from ACPI?

APM is the legacy power management scheme that was first supported in Windows 95. Most of the functionality for APM is in the computer-specific BIOS that is unaccessible to the operating system. APM powers down the computer to an acceptable power level when it was not in use.

As the computer platform has evolved and new capabilities and performance have been added to the computer, APM has no longer been able to meet power management requirements.

One example of this evolution is the integration of communication capabilities in the computer. On many computers with APM, communications connections are dropped when power is reduced. While in that state, the computer is unable to respond to any external event such as an incoming LAN packet or telephone call. Unlike APM, ACPI has the ability to control Plug and Play devices and all aspects of device power management.

You can use Device Manager as a method of checking for APM or ACPI support. Open Device Manager and select View devices by connection. Either Advanced Power Management or Advanced Configuration and Power Interface is one of the first devices in the list.