Power management

This topic briefly describes the PATROL Agent's support of application power management. It defines OnNow and ACPI and describes how they work. It then describes how the PATROL Agent supports OnNow/ACPI on Windows platforms.

ACPI definition and functions

ACPI is the Advanced Configuration and Power Interface. It succeeds Application Power Management (APM) and extends its capabilities. ACPI facilitates power management by making hardware status information available to the operating system. ACPI enables computers to perform the following tasks:

  • Manage power consumption, especially on portables, by turning on its peripherals and off
  • Be turned on and off by external devices or placed into a sleep state, so that the touch of a mouse or the press of a key will "wake up" the computer

OnNow definition and functions

OnNow is Microsoft's implementation of the Advanced Configuration and Power Interface (ACPI). It takes advantage of PC motherboards with BIOSes that support ACPI.

The OnNow feature allows a computer to always be on, and therefore instantly accessible to users, while consuming very little power when not in use.

Sleep state

Sleep state is a condition of power management that enables a system to suspend all processes. This suspension is a virtual shut down that permits a system to awaken and respond to commands without consuming much power. Following are the sleep states:

  • Hibernate
  • Stand by
  • Sleep

OnNow and ACPI operation

The following table describes how OnNow/ACPI-compliant applications and non-compliant applications behave when a system enters into sleep state and then awakens:




An internal or external device issues a command to go into sleep state.


The OnNow/ACPI function takes a snap shot of the system's state and all its applications by writing everything in memory to the hard drive.


Applications that support power options shut down their processes or die gracefully. Applications that do not support power options simply fail.


An internal or external device issues an awaken command.


The OnNow/ACPI function reads the information written to the disk and restores the state of OnNow-supported applications. It also attempts to restore the state of applications that do not support power management. These applications may not be recoverable because their processes are looping or suspended or startup information is unavailable because its owning data structures (such as files or databases) were corrupted during the shutdown.

PATROL Agent support for OnNow and ACPI

The OnNow/ACPI capabilities built into the PATROL Agent include the following:

  • Registering with the system during start up to receive power events; once enabled, the PATROL Agent service responds and processes the SERVICE_CONTROL_POWEREVENT control requests
  • Properly shutting down all processes when the system is placed in a sleeping state; this procedure reduces the chances that applications and files will be corrupted
  • Restarting the PATROL Console and PATROL Agent when the system is awakened and reestablishing connections without user intervention
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