Wake on Timer
Windows Vista systems are capable of waking from Sleep due to a timer event, such as a scheduled task or Windows Media Center television recording. The wake on timer feature enables the power manager to program the platform timer alarm to wake the system at a predetermined future time, based on requests from applications and services.
The global ability for the system to wake from timer is controlled in Windows Vista power policy. By default, the ability to wake from Sleep on timer is enabled for all power plans and both AC and DC power states.
Allow wake on timer
Allow Windows to automatically wake your computer from sleep on a timer for scheduled tasks and other programs.
The Windows power manager programs the platform timer alarm when the system enters the Sleep state. Disabling wake on timer for DC power prevents the power manager from programming the platform timer alarm if the system is on DC power when the computer enters Sleep. Similarly, disabling wake on timer for AC power prevents the power manager from programming the platform timer alarm when the system is on AC power and enters a Sleep state.
Disabling wake on timer can help extend usable mobile PC battery life by preventing the system from automatically waking from Sleep and allowing the system to wake from Sleep only when the user is ready to interact with the system again. System manufacturers designing ultraportable laptops for business and productivity use may want to disable the wake on timer policy.
However, it is important to note that if wake on timer is disabled, the following Windows functionality are not available on the system:
Hibernate idle time-out.
Windows Media Center television recording.
Scheduled tasks that are programmed to wake the computer from the Sleep state.
Automatic checks for new Windows Update if the preconfigured time occurs when the system is in the Sleep state.
Any other program or service that attempts to schedule a wakeable timer via the SetWaitableTimer