Tài liệu Power Management docx

By using the Power Options applet in the Control Panel, it is possible to decrease energy consumption by any device installed in the system.. Table 5.2 lists the registry keys that you c

Power Management

The power-management system in Windows 2000, Windows XP, and Windows Server

2003 is an integrated approach to power management within the whole computer system (for both hardware and software) This means that the computer system supporting power management must include both hardware and software support for the following

functions:

ƒ Minimum time expenses for startup and shutdown This means that the system may stay in a hibernation state as long as necessary It may "wake up" from this mode very quickly (this doesn't require rebooting)

ƒ Efficient and economic power consumption, meaning an increase in the working life of the hardware Devices consume power only when they process a system request or perform operations requested by the user Devices that aren't in use during a specified time period are switched to a "sleeping" state, and subsequently

"wake-up" as needed

ƒ Silent operation

Requirements for power-aware hardware and software are defined by the OnNow

initiative Windows XP and Windows Server 2003 provide this support and both the PC

as a whole and each individual device consume the minimum amount of power (if the hardware meets the OnNow requirements) Notice that power management and PnP are interrelated and depend on each other

This approach provides the following advantages:

ƒ Intelligent behavior by the system The operating system and applications work together to operate the PC, delivering effective power management in accordance with your current needs For example, applications won't inadvertently keep the

PC busy when they aren't necessary, they proactively participate in shutting down the PC to conserve energy and reduce noise

ƒ Improved robustness and reliability

ƒ Higher level of integration

By using the Power Options applet in the Control Panel, it is possible to decrease energy consumption by any device installed in the system However, this is only the case if you have an ACPI-compliant computer system

The Power Schemes Tab

To start the Power Options applet, proceed as follows:

1 From the Start menu, select Settings | Control Panel Double-click Power

Management

2 The Power Options Properties window will appear (Fig 5.13)

Figure 5.13: The Power Schemes tab of the Power Options Properties window

3 To reduce the power consumption of your computer devices - or of your entire

system - choose a power scheme, which is a collection of settings that manage the

power usage of your computer You can select one of the existing power schemes

or create a user-defined power scheme For example, depending on your hardware, you can do the following:

ƒ Specify the conditions where the system will automatically turn off your monitor and hard disks to save power

ƒ Put the computer on standby if it is idle for a long period of time While on standby, your entire computer switches to a low power state, where devices such as the monitor and hard disks turn off and your computer uses less power When you want to use the computer again, it comes out of standby quickly, and your desktop is restored exactly as you left it Standby is particularly useful for conserving battery power in portable computers

ƒ Put your computer in hibernation The hibernate feature saves everything in memory on disk, turns off your monitor and hard disk, and then turns off your computer When you restart your computer, your desktop is restored exactly as you left it It takes longer to bring your computer out of

hibernation than out of standby

Table 5.2 lists the registry keys that you can modify using the Power Schemes tab of the

Power Management Properties windows

Table 5.2: Registry Keys Modified Using the Power Schemes Tab Controls

Power Schemes option Registry key

Panel\PowerCfg\CurrentPowerPolicy Standby detection threshold values (for the

system, monitor, hard disk-System

hibernates, Turn off monitor, Turn off

hard disks fields, respectively)

Binary-encoded parameters

HKCU\Control Panel\

PowerCfg\PowerPolicies\n\Policies

Deleting the power scheme (the Delete

button)

Deletes the following key

HKCU\Control Panel\PowerCfg\

PowerPolicies\n\Policies

HKLM\SOFTWARE\Microsoft\Windows\ CurrentVersion\Controls

Folder\PowerCfg\LastID

Adding new power scheme (the Save As

button)

Adds new subkey under the following key:

HKCU\Control Panel\PowerCfg\

PowerPolicies\n\Policies

HKLM\SOFTWARE\Microsoft\Windows

\CurrentVersion\Controls Folder\PowerCfg\LastID

Generally, you need to turn off your monitor or hard disk for a short period of time to conserve power The most convenient mode for this is the standby mode, which puts your entire system in a low-energy state

The Hibernate Tab

Beside the standby mode, the Power Options applet allows you to put your system into hibernation mode As already mentioned, the hibernate feature saves everything in

memory on disk, turns off your monitor and hard disk, and then turns off your computer After rebooting the system, your desktop is restored exactly as you left it It takes longer

to bring your computer out of hibernation than out of standby

If you are planning to be away from your computer for any length of time, it is

recommended to put the system into hibernation To activate hibernation support,

proceed as follows:

1 Open the Power Options Properties window and go to the Hibernate tab (Fig 5.14) If your system doesn't support this option, the tab will be unavailable

Figure 5.14: The Hibernate tab of the Power Options Properties window

2 Set the Enable hibernate support checkbox Please note that when your

computer is set to hibernation, everything in the physical memory is saved to the hard disk Because of this, you need to have sufficient disk space on the hard disk (the file storing memory dump will be as large as your RAM)

After hibernation support is activated, the What do you want the computer to do? list

in the Shut Down Windows dialog will contain a new option - Hibernate, which allows

you to put the computer into hibernation manually (Fig 5.15)

Figure 5.15: When you enable hibernation support, the Shut Down Windows window will display a new option - Hibernate, allowing you to put the system to hibernation

manually

The Advanced Tab

The Advanced tab of the Power Options Properties window (Fig 5.16) allows you to

do the following:

Figure 5.16: The Advanced tab of the Power Options Properties window

ƒ Enable and disable the power options indicator on the taskbar (Fig 5.17) This indicator is a small icon that provides quick access to the Power Options applet

Figure 5.17: The taskbar indicator provides quick access to the Power Options applet

ƒ Enable and disable password protection for the standby mode

Registry keys that correspond to the parameters set using this tab are listed in Table 5.3

Table 5.3: Registry Keys Modified by Setting Parameters of the Advanced Tab

Always show icon on the taskbar checkbox HKCU\Control

Panel\PowerCfg

\GlobalPower

Table 5.3: Registry Keys Modified by Setting Parameters of the Advanced Tab

Policy\Policies

Display a prompt for a password when the computer

goes off standby checkbox

HKCU\Control Panel\PowerCfg

\Global PowerPolicy\Policies

The UPS Tab

If Uninterruptible Power Supply (UPS) is present in your system, it can also be managed via Power Options To configure and manage the UPS service, start the Power Options

applet in Control Panel, and go to the UPS tab (Fig 5.18) This tab displays the current power status, details on your UPS equipment and the current status of the UPS service

Figure 5.18: The UPS tab of the Power Options Properties window

Power Management Tools in Windows 2000, Windows XP, and Windows Server

2003

Having already discussed the power-management tools provided by Windows 2000, Windows XP, and Windows Server 2003, let's now discuss the basic concepts that allow these tools to be implemented

The topics covered here include:

ƒ Parameters included in the power scheme

ƒ How power-management settings specified by the Power Options Control Panel applet are stored in the registry

Power Schemes

Power management configuration in Windows 2000, Windows XP, and Windows Server

2003 is based on the concept of power schemes A power scheme is a group of preset power options that are passed to the Power Policy Manager component of the operating system to control the machine's power-management behavior

Each power scheme consists of a global power-policy structure and a power-policy structure

ƒ Global power-policy structures contain preset power options that are global across all power schemes

ƒ Non-global power-policy structures contain power options that are unique to a particular power scheme

These power-policy structures are further divided into machine structures and user

structures

registry key, and none of these values are exposed in the user interface For

example, you can't set any of these values using the Power Options applet in the Control Panel

and some of these values are displayed in the user interface Some of these

parameters can be set using the Power Options applet in Control Panel

The data structures defining power management policy are listed below:

structure contains the data common to all power schemes This structure is a container for a GLOBAL_USER_POWER_POLICY structure and a

GLOBAL_MACHINE_POWER_POLICY structure, which contains elements that are read from and written to the registry

GLOBAL_POWER_POLICY structure It contains the data common to all power schemes and users The elements in this structure are read from and written to the HKLM key in the registry

GLOBAL_POWER_POLICY structure It contains the data common to all power schemes for the user The elements in this structure are read from and written to the HKCU key in the registry

contains the data unique for all power schemes This structure is a container for the USER_POWER_POLICY and MACHINE_POWER_POLICY structures that contain the elements to be read from and written to the registry There is one

POWER_POLICY structure for each power scheme on a machine

structure It contains the data unique to each power scheme, but common to all users The elements in this structure are read from and written to the HKLM key in the registry

structure It contains the data unique to each user and power scheme The elements

in this structure are read from and written to the HKCU key in the registry

Registry Keys Intended for Power Management

In this section, we'll discuss the registry keys that are used for power management You may edit any of them using one of the registry editors

Note Changing registry entries responsible for power management won't have an

immediate effect Windows only reads settings from the registry when you log on,

when you click OK in Control Panel, or when a Powerprof.dll function is called on

to read the registry

The registry keys used for power management are listed below

battery-power-alarm event

ƒ HKCU\AppEvents\EventLabels\CriticalBatteryAlarm - descriptive name of a critical battery-power-alarm event

HKCU\AppEvents\Schemes\Apps\PowerCfg\LowBatteryAlarm\.Default,

HKCU\AppEvents\Schemes\Apps\PowerCfg\CriticalBatteryAlarm\.Current,

HKCU\AppEvents\Schemes\Apps\PowerCfg\CriticalBatteryAlarm\.Default - filenames of the WAV files that will play as a low and critical power-alarm events

ƒ HKCU\Control Panel\PowerCfg\CurrentPowerPolicy - index of current user and machine power policy

ƒ HKCU\Control Panel\PowerCfg\GlobalPowerPolicy\Policies - the user global power policy (binary encoded data)

n, where n = 0, 1, 2, etc

ƒ HKCU\Control Panel\PowerCfg\PowerPolicies\n\Description - descriptive string for power scheme n, where n = 0, 1, 2, etc

ƒ HKCU\Control Panel\PowerCfg\PowerPolicies\n\Policies - user power policy n, where n = 0, 1, 2, etc (binary encoded data)

Folder\PowerCfg\LastID - index of the last power policy in the lists of user and machine power policies (for example, if there are six user power policies and six machine power policies in the registry, the value of this key is 5)

Folder\PowerCfg\DiskSpinDownMax - the maximum disk spin-down time that Control Panel will allow the user to set

Folder\PowerCfg\DiskSpinDownMin - the minimum disk spin-down time that Control Panel will allow the user to set

Folder\PowerCfg\GlobalPowerPolicy\Policies - the machine global power policy (binary encoded data)

Folder\PowerCfg\PowerPolicies\n\Policies - machine power policy n, where n = 0,

1, 2, etc (binary encoded data)