Microsoft® Windows® XP Professional Resource Kit Documentation

Author Microsoft Corporation Pages 1744 Disk 1 Companion CD(s) Level Advanced Published 10/17/2001 ISBN 9780735614857 Price $59.99 To see this book's discounted price, select a reseller below.	More Information About the Book Table of Contents Sample Chapter Index Related Series Related Books About the Author Support: Book & CD Rate this book

Chapter 7: Supporting Mobile Users continued

Configuring Power Management

If you do not have an APM-based or ACPI-based computer, it is still possible to manage some aspects of power consumption. For example, depending on the capabilities of your hardware, you can reduce the power consumed by the computer by setting timers to turn the display or disk drives off.

ACPI Power Management

Each device class on the computer has a power policy owner. The policy owner for a particular device class is the component that is best aware of how the device is used. Typically this is the device class driver. Each policy owner must manage power appropriately for its class and work consistently with the operating system's policy for putting the computer into a low-power state. For example, a network adapter might sense that no network cable is plugged in, and therefore request that the operating system put the adapter in a low-power state because it is not being used.

In order to use the ACPI power management features in Windows XP Professional, your computer must have an ACPI-compliant BIOS that is compatible with Windows XP Professional.

During setup, Windows XP Professional determines which hardware abstraction layer (HAL) to install on the computer. If the computer has an ACPI-compliant BIOS, an ACPI HAL is installed and you are able to use ACPI power management features. If the computer does not have an ACPI-compliant BIOS, a non-ACPI HAL is installed and ACPI power management features are not available.

In order to determine which HAL to install, Windows XP Professional performs the following process during setup:

1. Windows XP Professional checks the ACPI BIOS tables during startup. These tables list the devices that are installed on the computer and their power management capabilities.

If this information is missing, or if the information is in the wrong form, a non-ACPI HAL is installed.

2. If the tables are correct, Setup determines whether the computer's BIOS is known to be incompatible with the ACPI standard.

If the BIOS is on the incompatible list, a non-ACPI HAL is installed.

3. If the BIOS is not on the incompatible BIOS list, Setup checks the BIOS date.

If the BIOS is not on the incompatible BIOS list, and the BIOS date is later than 1/1/99, an ACPI HAL is installed.

4. If the BIOS is not on the incompatible BIOS list, and the BIOS date is earlier than 1/1/99, Setup determines if the BIOS is known to be compatible with Windows XP Professional.

If the BIOS is compatible, an ACPI HAL is installed.

If the BIOS is not compatible, an earlier HAL is installed.

For more information about BIOS compatibility, see the Hardware Compatibility List link on the Web Resources page at http://www.microsoft.com/windows/reskits/webresources.

You can use Device Manager to determine whether your computer is operating in ACPI mode.

To determine whether Windows XP Professional is running in ACPI mode

1. In Control Panel, click Performance and Maintenance, and then click System.
2. In the System Properties dialog box, click the Hardware tab, and then click Device Manager.
3. In the details pane, click Computer.

If Advanced Configuration and Power Interface (ACPI) PC is listed under Computer, the computer is operating in ACPI mode.

If you have an ACPI BIOS, but Windows XP Professional is not installed in the ACPI mode, your ACPI BIOS might be noncompliant. Check with your computer manufacturer to see if a more recent, ACPI-compatible BIOS is available. If Windows XP Professional is installed in non-ACPI mode on your computer, and you upgrade to a new BIOS version, you must reinstall Windows XP Professional to enable ACPI mode. For more information about upgrading the BIOS on a portable computer, see the Hardware Update link on the Web Resources page at http://www.microsoft.com/windows/reskits/webresources.

You must be a member of the Administrators group to view the Hal.dll file to determine which hardware abstraction layer is installed.

APM Power Management

APM does not work with every APM-compatible system running Windows XP Professional. Microsoft has tested APM-capable systems to determine how well each system and BIOS combination supports APM.

Mobile systems can support APM if they meet the following criteria:

• Hardware must meet basic Windows XP Professional requirements.
• An ACPI-compliant BIOS is not available for end-user system upgrade.
• The APM 1.2-compliant BIOS is not on the "Disable APM List" for a particular BIOS version number and date.
• All user-defined CMOS power control features are disabled or minimized, time-outs are set to Off or to the longest possible time allowed, and the APM BIOS is enabled.

Determining APM BIOS Compatibility

In order for you to use APM-based power management features with Windows XP Professional, the APM-based BIOS on your computer must be compatible with Windows XP Professional.

Windows XP Professional supports APM version 1.2 on portable computers. The portable computer, however, must have an APM-compatible BIOS in order for APM features to work properly. Windows XP Professional determines whether a BIOS is APM-compatible during setup, and on the basis of this determination, does one of the following:

• Installs APM support (Ntapm.sys and Apmbatt.sys) and enables APM if the computer's BIOS is found on the auto-enable APM list.
• Does not install or enable APM support if the computer's BIOS is found on the disable APM list. APM on these systems does not work reliably, and if used, data loss might occur.
• Installs APM support but does not enable APM support if the computer's BIOS is not on the auto-enable APM list or the disable APM list. APM might work properly, but you must enable APM in the Windows XP Professional graphical user interface (GUI). For more information about enabling APM, see "Configuring APM BIOS" later in this chapter.

If APM is not enabled after you install Windows XP Professional, either the computer's BIOS is on the disable APM list, or it is not on the auto-enable APM list. You can determine whether either of these is the case by using the Apmstat.exe tool, which is included with the Windows XP Professional Support Tools on the Microsoft^® Windows^® XP Professional operating system CD.

To determine APM BIOS compatibility by using Apmstat.exe

• At the command prompt, type:

apmstat

If Apmstat.exe reports that an APM BIOS is not known to be compatible and it is not known to be incompatible, you might still be able to use APM, but you must enable and configure APM so that it works properly on your computer.

To verify that APM support is installed on a computer

1. In Control Panel, click Performance and Maintenance, and then click System.
2. Click the Hardware tab, and then click Device Manager.
3. On the View menu, click Show hidden devices.

If NT Apm/Legacy Support is listed in the details pane, APM support is installed.

To enable APM

1. In Control Panel, click Performance Maintenance, and then click Power Options.
2. Click the APM tab.
3. Under Advanced Power Management, select the Enable Advanced Power Management support check box.

Configuring APM BIOS

In order to utilize APM power management on your system, you must configure an APM-based BIOS so that power management works properly with Windows XP Professional. This might involve configuring the APM BIOS in the following way:

1. Set BIOS time-outs to the maximum time or disable them. This allows the operating system (instead of the BIOS) to control time-outs. Because some APM BIOSs turn off or refuse to function if all time-outs are disabled, you might want to set time-outs to the maximum allowed time instead of disabling them.
2. Make sure that screen blanking is turned off in the BIOS. Typically, you can turn off screen blanking in the BIOS by disabling the time-out for the display or by setting the time-out to the maximum value. Screen blanking reduces power to the display, which causes the computer to appear to be shut down.

Activating a pointing device typically wakes the system and restores power to the display. However, USB and other external pointing devices do not wake the system or restore power to the display.

Do not use a supplemental video card with a portable computer if you use APM. Use only the video card included with the portable computer. The APM BIOS might not detect a video card that is added to the system or a video card that is in a docking station. If the adapter is not discovered by the APM BIOS, the suspend feature does not work.

Power Management Schemes and Options

Configuring Power Schemes

Using power schemes, you can configure how and when a computer turns off devices, enters a suspend state, or changes processor performance levels on mobile systems that support this function. You can configure these settings according to the power source in use — whether the computer is plugged into a wall outlet or powered by battery. Depending on the hardware capability, you might be able to configure some of these settings even if the computer is not ACPI- or APM-enabled.

The following default power schemes are available in Windows XP Professional: Home/Office Desk, Portable/Laptop, Presentation, Always On, Minimal Power Management, and Max Battery. You can customize any scheme, or add or delete new schemes to fit a specific situation.

For more information about configuring the standby feature and the hibernate feature, see "Configuring Hibernation and Standby" later in this chapter.

The default power scheme on portable computers is Portable/Laptop; the Home/Office Desk scheme does not optimize battery power. You might need to change the power scheme based on how the computer is used. For example, you might choose the Presentation scheme to prevent the computer from turning off the display during a presentation.

To configure a power scheme

1. In Control Panel, click Performance and Maintenance, and then click Power Options.
2. Click the Power Schemes tab.
3. Select a power scheme. You can then change the settings in the power scheme to best meet your needs.

Configuring Hibernation and Standby

When a computer enters hibernation, the current state of the computer is saved to disk, and the power to the computer is turned off. When a computer wakes from hibernation, it reads the current state data from the disk and restores the system to the state that it was in before it entered hibernation. All programs that were running are restarted, and network connections are restored.

Hibernation is enabled by default. All ACPI-compatible and most APM-compatible computers can be set to enter hibernation.

Because the contents of the computer's memory are written to disk when the computer enters hibernation, you must have at least as much available disk space as you have memory.

To disable hibernation

1. In Control Panel, click Performance and Maintenance, and then click Power Options.
2. Click the Hibernate tab.
3. Clear the Enable hibernate support check box.

When a computer enters standby, the computer's state is saved to memory and most circuitry and devices are turned off. When a computer resumes from standby, the state is restored from memory and power is restored to all devices. If power is interrupted when the computer is in standby, data might be lost. All installed devices and device driver software must properly support power management in order for standby to be available.

To provide security, you can have the computer prompt the user for a user name and password after it resumes from hibernate or standby. Password protection is enabled by default.

To disable password protection when a computer resumes from standby

1. In Control Panel, click Performance and Maintenance, and then click Power Options.
2. Click the Advanced tab.
3. Clear the Prompt for password when computer goes off standby check box.

Configuring the Group Policy Refresh Interval for Hibernation or Standby

You can configure the refresh interval by using Group Policy, which controls how often policies are applied on the computer. By default, the refresh interval is 90 minutes, but it can be set to any value between 0 and 64,800 minutes. You can also set an interval offset, which is a random period of time that is applied to the refresh interval. Randomizing the refresh interval prevents clients with the same refresh interval from overloading the server by simultaneously requesting policy updates. By default, the interval offset is 30 minutes, meaning that a random time between 0 and 30 minutes is applied to the refresh interval.

In some cases, Group Policy refresh settings can prevent a computer from entering hibernation or standby. This is because a policy update resets the hibernation or standby timer (as moving the mouse or pressing a key does). For example, if a computer is set to enter hibernation or standby after being idle for 45 minutes, but the Group Policy refresh interval is set at 30 minutes, the hibernation or standby timer never reaches 45 minutes. To ensure that the standby timer reaches 45 minutes (or whatever time you set), set the Group Policy refresh interval so that it is greater than the hibernation setting or standby setting in Power Options. You can also configure Group Policy so that it does not apply settings while the computer is being used.

To change the Group Policy refresh interval and the interval offset for User Configuration settings

1. In the Run dialog box, type gpedit.msc.
2. In the details pane of Group Policy, under User Configuration, open the Administrative Templates folder, and then open the System folder.
3. Click Group Policy.
4. In the details pane, double-click Group Policy refresh interval for users.
5. Click Enabled.
6. Change the settings for the refresh interval and the interval offset.

To change the Group Policy refresh interval and interval offset for Computer Configuration settings

1. In the details pane of Group Policy, under Computer Configuration, open the Administrative Templates folder, and then open the System folder.
2. Click Group Policy.
3. In the details pane, double-click Group Policy refresh interval for computers.
4. Click Enabled.
5. Change the settings for the refresh interval and the interval offset.

To disable policy updates while a computer is running

1. In the Run dialog box, type gpedit.msc.
2. In the details pane of Group Policy, under Computer Configuration, open the Administrative Templates folder, and then open the System folder.
3. Click Group Policy.
4. In the details pane, double-click Disable background refresh of Group Policy.
5. Click Enabled.

Configuring Battery Monitoring and Management

Windows XP Professional allows you to monitor and manage a portable computer's battery by using Power Meter. Windows XP Professional can also monitor multiple batteries. Battery monitoring and management are only available on ACPI-enabled and APM-enabled computers.

By default, the battery status icon will appear on the taskbar whenever the computer is operating on battery power. You must enable the battery status icon to make it appear on the taskbar at all times. This icon gives users direct access to the power meter feature, allows selection of the current power scheme, and offers direct access to power properties by means of the Power Options Control Panel option.

To add the battery status icon to the taskbar

1. In Control Panel, click Performance and Maintenance, and then click Power Options.
2. Click the Advanced tab.
3. Select the Always show icon on the taskbar check box.

If your portable computer uses multiple batteries, you can also configure the battery meter to display the status of multiple batteries.

To configure the battery meter for multiple-battery computers

1. In Control Panel, click Performance and Maintenance, and then click Power Options.
2. Click the Power Meter tab.
3. Click Show details for each battery.

You can set alarms to indicate low-battery and critical-battery levels. You can select visual and audible alarm notifications, specify an action to take such as making a change in power state (standby, hibernation, shutdown), and specify the execution of a program to be run.

To configure alarms to indicate low-battery and critical-battery levels

1. In Control Panel, click Performance and Maintenance, and then click Power Options.
2. Click the Alarms tab.
3. Set the battery activation levels that you want.
4. Click Alarm Action to configure the behaviors of an activated alarm.

Configuring Power Button, Sleep Button, and Lid Switch Behavior

ACPI-enabled mobile computers can have up to three buttons for controlling system power: a Power button, a Sleep button, and a Lid Switch. Windows XP Professional allows you to configure the action of each button as follows:

• Do nothing
• Ask me what to do
• Sleep
• Hibernate
• Shut down

To configure power system button functionality

1. In Control Panel, click Performance and Maintenance, and then click Power Options.
2. Click the Advanced tab.
3. Under When I close the lid of my portable computer, select a lid-switch action.
4. Under When I press the power button on my computer, select a power-button action.
5. Under When I press the sleep button on my computer, select a sleep-button action.

Enabling Devices to Wake the Computer

On ACPI-compatible systems, Windows XP Professional can enable some devices to wake the system from the hibernation or standby. Windows XP Professional supports wake events such as modem wake–on-ring, wake–on-LAN, and wake–on-critical battery. Windows XP Professional also supports wake–on-LAN for CardBus network adapters. Note that in order for the wake features to function, they must be supported by the appropriate computer hardware.

To enable a device to wake the computer

1. In Control Panel, click Performance and Maintenance, and then click System.
2. Click the Hardware tab, and then click Device Manager.
3. Select the device that you want to wake the system, and then double-click to open the Properties dialog box.
4. On the Power Management tab, click Allow this device to bring the computer out of standby.

If no Power Management tab appears, the device does not support system wake.

Hiding Power Options

You can prevent users from configuring power options by specifying Control Panel settings in Group Policy. You can disable Control Panel entirely, hide specific Control Panel tools, and show specific Control Panel options. Hiding Power Options can be beneficial if you have configured the power options, and you do not want users to change those options. However, if you hide Power Options, users have no means to reconfigure power management settings if they need to be changed while they are away from the office. For example, portable computer users frequently use the Portable/Laptop power scheme. When they use the portable computer for a presentation, however, it is recommended that they switch to the Presentation scheme to prevent the portable computer from turning off the display or entering standby or hibernation during the presentation. Users cannot change power schemes, or any other power option, if Power Options is not available.

To hide Power Options by using Group Policy settings

1. In the Run dialog box, type gpedit.msc.
2. In the Group Policy console tree, under User Configuration, open Administrative Templates.
3. Click the Control Panel folder.
4. In the details pane, double-click Hide specified control panel applets.
5. In the Hide specified Control Panel applets Properties dialog box, click Enabled, and then click Show.
6. Click Add.
7. Type power options.

Typically, Power Options appears in the Show Contents dialog box, under List of disallowed control panel applets.

To disable Control Panel by using Group Policy settings

1. In the Run dialog box, type gpedit.msc.
2. In the Group Policy console tree, under User Configuration, open the Administrative Templates folder.
3. Click the Control Panel folder.
4. In the details pane, double-click Disable Control Panel.
5. Click Enabled.

Last Updated: October 3, 2001

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