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Power management settings control the
behavior of a computer in different power use situations, such as when
it is plugged in or running on a battery. Although all computers should
be configured with power management settings to save energy, power
management settings on laptops help to balance performance against
energy usage. In some cases, you’ll want to reduce laptop responsiveness
and overall performance to increase the battery life, enabling the
laptop user to run the laptop on battery for longer periods of time. In
other cases, you might want to ensure moderate performance and a
moderate battery life, or you might want to ensure maximum performance
regardless of how this affects battery life.
The core aspects of power management are managed using power plans, which are collections of power
management settings that control power usage and consumption. A
computer can have multiple power plans, but only one can be active at
any given time. In addition to power plans, most computers have preset
behaviors for when the power button is pressed and for when the sleep
button is pressed, and laptops have a default action for when you close
the laptop’s lid. Typically, closing a laptop’s lid puts it into sleep
mode, pressing and holding the power button shuts down a computer, and
pressing the sleep button puts a computer into sleep mode. Through
systemwide settings for power options, you can customize the power
button and password-protection-on-wakeup behavior to meet the needs of
individual users or groups of users.
1. Managing Power Options from the Command Line
Windows 8 includes the Power
Configuration (Powercfg.exe) utility for managing power options from
the command line. You can view a list of parameters for this utility by
typing powercfg /? at a command prompt. The parameters you’ll work with most often include:
-
–a Lists the available sleep states on the computer and the reasons why a particular sleep state is not supported. -
–d [guid] Deletes the power plan specified by the globally unique identifier (GUID). -
–devicequery all_devices_verbose
Lists detailed power support information for all devices on the
computer. Be sure to redirect the output to a file because this list is
very long and detailed. -
–energy Checks the
system for common configuration, device, and battery problems and then
generates an HTML report in the current working directory. -
–h Toggles the hibernate feature on or off. -
–l Lists the power plans configured on a computer by name and GUID. -
–q [guid] Lists
the contents of the power plan specified by the GUID. If you don’t
provide a GUID, the contents of the active power plan are listed. -
–requests Displays
all power requests made by device drivers. If there are pending
requests for the display, these requests would prevent the computer from
automatically powering off the displays. If there are pending requests
for any device including the display, these requests would prevent the
computer from automatically entering a low-power sleep state. -
–s [guid] Makes the power plan specified by the GUID the active power plan. -
–x [setting] [value] Sets the specified value for the specified setting in the active power plan.
Note
By default, Windows 8 computers use hybrid sleep instead of
hibernate. Hibernate should not be configured without first determining
compatibility. Note also that the Power
Configuration utility (Powercfg) accepts either a hyphen (-) or a slash
(/) for commands. I prefer to use a hyphen because of its location on
the keyboard.
The following is a sample listing returned by typing powercfg –l at a command prompt:
Existing Power Schemes (* Active)
-----------------------------------
Power Scheme GUID: 381b4222-f694-41f0-9685-ff5bb260df2e (Balanced)
Power Scheme GUID: 8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c (High performance)
Power Scheme GUID: a1841308-3541-4fab-bc81-f71556f20b4a (Power saver)
Power Scheme GUID: c1d97820-3148-42a9-a587-75d618a9bb2b (Graphics Dept) *
The active plan is marked with an asterisk. From this listing, you
can determine that this computer has four power plans and the active
power plan is the Graphics Dept plan.
If you want to configure power plans or modify power settings using
Powercfg, you need to do so by using an elevated command prompt. When a
parameter requires a GUID, the easiest way to obtain this value is to
type powercfg –l at
an elevated command prompt, and then copy the value for the appropriate
power plan. For example, if you want to make the Balanced plan the
default plan for the computer in the previous example, you would type
the following at an elevated command prompt:
powercfg -s 381b4222-f694-41f0-9685-ff5bb260df2e
You determine the power modes that a computer supports by typing powercfg –a at a command prompt. Powercfg will list exactly what modes are and aren’t supported, such as the following:
The following sleep states are available on this system:
Standby (S1 S3)
Hibernate
Hybrid Sleep
The following sleep states are not available on this system:
Standby (S2)
The system firmware does not support this standby state.
If a computer has problems entering sleep or hibernate mode, you can
use powercfg –a to possibly determine what is causing the problem. If
the firmware doesn’t support a particular mode, you may in some
(limited) cases be able to update the firmware to gain support for a
particular mode. If a device that doesn’t support a particular mode is
causing a problem, you may be able to remove the device and replace it
with a compliant device.
Any time you want to evaluate a computer’s power configuration and
device compatibility, you can generate a Power Efficiency Diagnostics
report by entering powercfg –energy
at a command prompt. When you run powercfg –energy, the report is
generated as an HTML document called Energy-Report.html. In the report,
you’ll see the results of power management compliance for devices. Any device that doesn’t support power
management appropriately will be listed, along with the error details.
For example, if a USB device doesn’t properly enter the Suspend state,
you’ll see the detailed information about the errors encountered and the
device configuration. If a power
management capability has been disabled due to a compatibility issue,
you’ll see this. For example, if the PCI Express Active-State Power
Management feature isn’t supported on the hardware and the feature has
been disabled because of this, you’ll see this listed in the report.
Warnings and additional information about devices and compatibility are
provided as well, including details on supported sleep states and
processor power management capabilities.
Note
REAL WORLD For laptops,
important information is provided on battery charging and battery life.
If a battery is nearing or at the end of its useful life, you’ll be able
to tell this because the battery life is limited and the battery
details will show the battery isn’t holding a charge like it should.
You’ll then know you need to replace the laptop’s battery.
To dig even deeper into power management issues, you can get
comprehensive power support details for every device on the computer by
entering the following command:
powercfg -devicequery all_devices_verbose > power.txt
where Power.txt is the name of the file in the current working directory in which the power information will be saved.
When you’ve configured Windows PowerShell for remoting, you can
easily execute Powercfg on multiple remote computers. To do this, enter
the name of each remote computer to check on a separate line in a file
called Computers.txt, and then save this file. Then open an elevated
administrator Windows PowerShell prompt and enter the following
commands:
$comp = get-content c:\computers.txt
$s = new-pssession -computername $comp
invoke-command -session $s { powercfg.exe -energy }
Here, C:\Computers.txt is the path to the Computers.txt file. Update
this path as appropriate for where you saved the file. On each computer,
an Energy-Report.html file will be created in the default directory for
the user account used to access the computer. If you would rather not
have to retrieve the HTML document from each computer, you can write the
report to a share and base the report name on the computer name, as
shown in the following example:
$comp = get-content c:\computers.txt
$s = new-pssession -computername $comp
invoke-command -session $s { powercfg.exe -energy -output
"\\fileserver46\data\$env:computername.html"}
Here, you write the report to the \\fileserver46\data share and name the file using the value of the ComputerName
environment variable. Note that when you work with Windows PowerShell
and are referencing commands with executables, you must specify the .exe
file extension with the program name.
2. Working with Power Plans
On mobile computing devices, the notification area of the taskbar
includes a Power icon. Tapping or clicking this icon shows the battery
state and the power plan that you are using. Tapping or clicking either
of the links provided in the notification status dialog box opens the
Power Options page in Control Panel. Out of the box, most configurations
of Windows 8 have three preferred power plans:
-
Balanced
A power usage plan
that balances energy consumption and system performance. The processor
speeds up when more resources are used and slows down when less are
needed. This is the default power plan. Use this plan for users who work
with a wide variety of applications, including those that are
moderately graphics-intensive, such as Microsoft PowerPoint, and those
that are not graphics-intensive, such as Microsoft Word and Microsoft
Outlook. -
High Performance
A high-power usage
plan that optimizes the computer for performance at a direct cost to
battery life. This plan ensures that you always have enough power for
using graphics-intensive programs or playing multimedia games. Use this
plan when performance is essential and users work primarily with
graphics-intensive applications or applications that perform complex
arithmetic calculations. Note that you may have to tap or click Show
Additional Plans to view this power plan. -
Power Saver
A low-power usage
plan designed to reduce power consumption. This plan slows down the
processor to maximize the battery life. Use this plan for users who work
primarily with non-graphics-intensive applications, such as Word and
Outlook.
Power plan settings are divided into two general categories: basic
and advanced. Basic power settings control when a computer dims or turns
off its display, as well as when the computer enters sleep mode. It’s
important to note that mobile computing devices have On Battery and
Plugged In settings that can be configured independent of each other.
For example, you may want a computer’s display to dim after 2 minutes of
inactivity when on battery or after 5 minutes of inactivity when
plugged in.
Advanced power settings determine precisely whether and when power
management components on a computer are shut down and how those
components are configured for performance. The advanced power settings
available depend on the computer’s configuration and include:
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Battery\Reserve Battery Level
Determines the
percentage of battery remaining that initiates reserve power mode.
Typically, the default value is 7 percent, meaning the computer will
enter reserve power mode when there is 7 percent of battery power
remaining. Although you can set any percentage, a reserve level of 5 to
18 percent is often best. -
Desktop Background Settings\Slide Show
Determines whether
the slide show feature for the desktop background is available or
paused. The default setting is Available. If you set this option to
Paused, background slide shows on the desktop will be disabled. -
Display\Turn Off Display After
Determines whether and when a computer’s display is turned off to conserve power.
Use a setting of Never to disable this feature. Use a specific value in
minutes to determine how long the computer must be inactive before the
display is turned off. -
Hard Disk\Turn Off Hard Disk After
Determines whether and when a computer’s hard disk is turned off to conserve power.
Use a setting of Never to disable turning off the hard disk. Use a
specific value in minutes to determine how long the computer must be
inactive before the hard disk is turned off. Windows 8 provides a combo
box for setting numeric values. Tapping or clicking and holding the up
or down arrow enables you to rapidly scroll through values. If you
scroll down from 1, the next value is Never. You can also type a value.
If you enter a value of 0, this is interpreted as Never. -
Multimedia Settings\When Playing Video
Determines the power
optimization mode used when playing video. If you set this option to
Optimize Video Quality, the computer will use the best playback quality
possible for video. If you set this option to Balanced, the computer
will use a balanced approach, adjusting playback quality to some degree
to save power. If you set this option to Optimize Power Savings, the
computer will actively adjust the playback quality to save power. -
Multimedia Settings\When Sharing Media
Determines what the
computer does when a device or another computer plays media from the
computer. If you set this option to Allow The Computer To Enter Away
Mode, the computer will not enter sleep mode when sharing media with
other devices or computers. If you set this option to Allow The Computer
To Sleep, the computer can enter sleep mode after an appropriate period
of inactivity regardless of whether media is being shared with other
computers or devices. If you set this option to Prevent Idling To Sleep,
the computer will enter sleep mode when sharing media with other
devices or computers only if a user puts the computer in sleep mode. -
PCI Express\Link State Power Management
Determines the power
saving mode to use with PCI Express devices connected to the computer.
You can set this option to Off, Moderate Power Savings, or Maximum Power
Savings. -
Power Buttons And Lid\Power Button Action
Specifies the action
to take when someone pushes and holds the computer’s power button. You
can set this option to Do Nothing, Sleep, Hibernate, or Shut Down. -
Power Buttons And Lid\Sleep Button Action
Sets the default
action for the sleep button. Use this setting to override the computer’s
default action. You can set this option to Do Nothing, Sleep, or
Hibernate. You cannot, however, use an option that is not supported by
the computer. -
Processor Power Management\Maximum Processor State
Sets a maximum or
peak performance state for the computer’s processor. To save power and
reduce energy consumption, lower the permitted maximum performance
state. But you lower the performance state at a direct cost to
responsiveness and computational speed. Although reducing the maximum
processing power to
50 percent or less can cause a significant reduction in performance and
responsiveness, it can also provide a significant power savings. -
Processor Power Management\Minimum Processor State
Sets a minimum performance state for the computer’s processor. To save power
and reduce energy consumption, lower the permitted minimum performance
state—but you lower the performance state at a direct cost to
responsiveness and computational speed. For example, a value of 5
percent would lengthen the time required to respond to requests and
process data while offering substantial power savings. A value of 50
percent helps to balance responsiveness and processing performance while
offering a moderate power savings. A value of 100 percent would
maximize responsiveness and processing performance while offering no
power savings. -
Processor Power Management\System Cooling Policy
Determines whether
the operating system increases the fan speed before slowing the
processor. If you set this option to Passive, this feature is limited,
and the processor may run hotter than normal. If you set this option to
Active, this feature is enabled to help cool the processor. -
PlanName\Require A Password On Wakeup
Determines whether a
password is required when a computer wakes from sleep. You can set this
option to Yes or No. With domain computers, this option is set to Yes
and can be controlled only through Group Policy. -
Sleep\Allow Hybrid Sleep
Specifies whether the computer uses Windows 8 sleep mode rather than
the sleep mode used in earlier versions of Windows. You can set this
value to On or Off. Hybrid sleep mode puts the computer in a low-power
consumption state until the user resumes using the computer. When
running on battery, laptops and tablets continue to use battery power in
the sleep state, but at a very low rate. If the battery runs low on
power while the computer is in the sleep state, the current working
environment is saved to the hard disk, and then the computer is shut
down completely. This final state is similar to the hibernate state used with Windows XP. -
Sleep\Allow Wake Timers
Determines whether timed events should be allowed to wake
the computer from a sleep state. If you set this option to Disable,
timed events won’t wake the computer. If you set this option to Enable,
timed events can wake the computer. -
Sleep\Hibernate After
Determines whether
and when a computer hibernates to conserve power. When a computer goes
into hibernation, a snapshot of the user workspace and the current
operating environment is taken by writing the current memory to disk.
When a user turns the computer back on, reading the memory from disk
restores the user workspace and operating environment. In Windows 8,
this setting isn’t normally used because the standard configuration is
to sleep after a period of inactivity. Use a setting of Never to disable
this feature. Use a specific value in minutes to determine how long the
computer must be inactive before the computer hibernates. -
Sleep\Sleep After
Determines whether and when a computer enters a sleep state to conserve power.
Use a setting of Never to disable this feature. Use a specific value in
minutes to determine how long the computer must be inactive before the
computer enters a sleep state. -
USB Settings\USB Selective Suspend Setting
Determines whether
the USB selective suspend feature is available. If you set this option
to Disabled, selective suspend will not be used with USB devices. If you
set this option to Enabled, selective suspend can be used with USB
devices. -
Wireless Adapter Settings\Power Saving Mode
Specifies the power
saving mode to use with any wireless adapters connected to the computer.
You can set this option to Maximum Performance, Low Power Saving,
Medium Power Saving, or Maximum Power Saving.
As you can see, the advanced power settings control every facet of power management. The differences in the advanced settings are what really set the power
plans apart from each other. For example, while the High Performance
plan ensures performance by allowing the computer’s processor to always
run at 100 percent power consumption, the Power Saver and the Balanced
plans reduce energy consumption by configuring the processor to use a
minimum power consumption rate of 5 percent and a maximum rate of 100
percent.
When configuring power
plans, it is important to allow components to turn off after periods of
inactivity. Turning off components separately enables a computer to
progressively go into sleep mode. When a computer is fully in sleep
mode, all power-manageable components are switched off so that the
computer uses less power. When the computer is brought out of sleep
mode, the components, such as the monitor and hard disks, are turned
back on, restoring the user workspace. You should configure sleep mode
so that when a laptop is running on batteries, it goes into power
conservation mode when the user is away from the laptop for a relatively
short period of time, such as 20 or 30 minutes.
Because a computer can have multiple power
plans, each plan can be optimized for the way a laptop is used at a
particular time. You can configure multiple power plans for different
situations. At home or in the office, laptops might need different power
management configurations than they do when users are giving
presentations. In one case, you might want to configure the laptop to
quickly conserve energy when running on batteries. In another case, you
might want to ensure that the laptop never turns off its hard disk or
wireless adapters.
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