Microsoft KB Archive/937556

= Description of the default behavior of a Windows Vista-based desktop computer when it wakes up from sleep =

Article ID: 937556

Article Last Modified on 10/31/2007

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APPLIES TO


 * Windows Vista Home Basic
 * Windows Vista Home Premium
 * Windows Vista Ultimate
 * Windows Vista Business
 * Windows Vista Enterprise
 * Windows Vista Home Basic 64-bit Edition
 * Windows Vista Home Premium 64-bit Edition
 * Windows Vista Ultimate 64-bit Edition
 * Windows Vista Business 64-bit Edition
 * Windows Vista Enterprise 64-bit Edition

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INTRODUCTION
This article describes the default behavior of a Windows Vista-based desktop computer when you wake it from sleep and when it wakes up automatically. Additionally, the article introduces some power management tools. The computer may run better if you use these tools.



System power states in Windows Vista
The behavior of a Windows Vista-based desktop computer when it wakes up from sleep does not depend on how it went to sleep.

Windows Vista uses the following four power states:

System power state S1
System power state S1 is a sleep state. This power state has the following characteristics:
 * The computer consumes less power than it consumes in system power state S0 (the system working state).
 * The computer consumes more power than it consumes in other sleep states.
 * The processor clock is off.
 * The bus clocks are stopped.

System power state S2
System power state S2 is a sleep state. System power state S2 resembles system power state S1. However, in system power state S2, the CPU context and contents of the system cache are lost because the processor loses power.

This power state has the following characteristics:
 * The processor is off.
 * The bus clocks are stopped.
 * Some buses might lose power.

System power state S3
System power state S3 is a sleep state. This power state has the following characteristics:
 * The computer consumes less power than it consumes in system power state S2.
 * The processor is off.
 * Some chips on the motherboard may also be off.

System power state S4
System power state S4 is the hibernate state. System power state S4 is the lowest-powered sleep state. Also, system power state S4 has the longest wake-up latency.

For more information about these system power states, visit the following Microsoft Web site:

http://msdn2.microsoft.com/en-us/library/ms798270.aspx

Sleep states and the monitor
After you put the computer in the hibernate state, Windows Vista automatically turns off the monitor. The computer wakes up, and Windows Vista turns on the monitor when one of the following events occurs:
 * The computer receives network traffic.

Note To set the computer to automatically wake up when the computer receives network traffic, you must turn on the wake from sleep option of a network adapter that supports the Wake On LAN (WOL) functionality.
 * You manually wake the computer.

Windows Vista turns on the monitor when the computer wakes up regardless of the event that makes the computer wake up. This behavior occurs because a re-post process occurs when you wake up the computer from hibernate state. In the re-post process, the computer loses the information about the events that make the computer wake up. Therefore, Windows Vista cannot tell the difference between a wake-up that you initiate and an automatic wake-up.

After you put the computer in a sleep state other than the hibernate state, Windows Vista automatically turns off the monitor. The computer wakes up when one of the following events occurs:
 * The computer receives network traffic.
 * You manually wake up the computer.
 * Windows Vista detects keyboard activity or mouse activity.

When the computer receives network traffic, Windows Vista does not turn on the monitor. However, when you manually wake up the computer, and when Windows Vista detects keyboard activity or mouse activity, Windows Vista turns on the monitor. This behavior occurs because in these situations, a component sends a request to call the SetThreadExecutionState function together with the ES_DISPLAY_REQUIRED flag.

Power management tools
You can use the Powercfg tool to control the computer's power settings. To view the current power configuration, run the powercfg -q command at a command prompt.

You can also test the computer configuration and the computer's response to different system power states. To do this, use the power management test tool (PwrTest.exe). PwrTest.exe is included in the Microsoft Windows Driver Kit (WDK). After you install Microsoft WDK, PwrTest.exe is in the Tools\Acpi\PwrTest folder. To view Help, run the Pwrtest /? command at a command prompt.

For more information about the power management test tool, visit the following Microsoft Web site:

http://msdn2.microsoft.com/en-us/library/aa906552.aspx

Away mode
Away mode is a new feature in Windows Vista that is designed for Media Center computers. When a computer is in away mode, Windows Vista turns off the display and mutes the analog audio. If you turn away mode off, the computer goes to sleep after the computer is idle for two minutes.

When the computer goes back to sleep
After the computer wakes up, the computer goes back to its previous sleep state if the computer is idle for a certain time. For example, this behavior may occur after the computer wakes up to automatically install a Windows update.

Keywords: kbhowto kbinfo kbexpertiseadvanced KB937556

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