Windows 7 Power Management: Applying Power Settings with POWERCFG

By , May 7, 2010 9:14 am

Between Windows XP and Windows 7, Microsoft made significant changes under the hood to power management in order to make Windows a more energy efficient OS. While Windows Vista included a significant number of changes to power management, it really seems like Microsoft put much more effort into making Windows 7 more power efficient after complaints about terrible battery life with Windows Vista. This PDF provides a general overview of these changes. Many of the changes work out of the box, which is great for overworked sysadmins. However, there are a few settings that need to be configured as needed, particularly when it comes to system idle and standby settings. With Windows 7, Microsoft has included several additional features and troubleshooting tools that address some of the headaches caused by power management in Windows XP.

Standby Me

Before we dive into the guts of power management in Windows 7, let’s discuss the value of taking the time to configure power management settings.  Since going green is a hot trend right now, many companies are starting to put pressure on sysadmins to find ways to squeeze power savings from a major offender to the energy grid: Computers. At many companies, workstations are left running 24×7, even when not in use. If the work week is only 40 hours, that means that many of these computers are in a Powered On with Nothing to Do (POND) state for 100+ hours per week.  As Ford recently discovered, turning computers off when they are not in use is a great way to reduce energy waste and save some serious coin!

One disadvantage to turning off computers completely when not in use is that, when a user needs to use the computer again, they have to wait for the computer to start up, then log in, then load applications and documents again. Admittedly, this a bit time consuming and frustrating for an end user.  Therefore, many sysadmins opt to put computers into a low power standby mode as a fair compromise between user experience and energy savings. Standby mode, which powers down most system components as suspends the system state to RAM, allows the user instantly resume where they left off when they last used the computer. In modern computers, standby only consumes slightly more power than when in a powered off state.

Applying Settings with POWERCFG

If you’ve used the POWERCFG utility in Windows XP, you’ll probably find one major difference in Windows 7: GUIDs. In Windows XP, a power scheme could be configured by specifying the name of the scheme in the POWERCFG command line syntax. In Windows 7, that is no longer an option. Instead, you must specify the GUID associated with a particular power scheme when configuring and activating a scheme. While POWERCFG in Windows 7 still includes a way to change the monitor, disk, and standby timeouts of the active scheme, it takes some understanding of the Windows 7 power management GUIDs to do anything beyond that. Not only are the power schemes themselves identified by GUIDs, Windows 7 uses GUIDs to uniquely identify settings and groups of settings as well. While the idea of working with GUIDs may seem like a daunting task, it’s actually pretty easy to wrap your head around once you know how to find and use these GUIDs.

The most straightforward way to get a list of power scheme, group, and setting GUIDs is to run POWERCFG -QUERY. As a side note, this command tends to generate a lot of output, so it may be wise to pipe the output to a file like this:

POWERCFG.EXE -QUERY > powercfg.txt

After running the command, the current directory should contain the powercfg.txt file with the output from POWERCFG – QUERY inside of it. Here’s what it looks like:

An example of the output from the POWERCFG -QUERY command

As you can see from the example above, POWERCFG -QUERY provides very detailed information about every power scheme and setting set in power options in a nicely indented format. At the top is the GUID associated with the power scheme (High Performance). Directly below that is the GUID that identifies the first subgroup of settings (settings belonging to no subgroup). The GUIDs that identify each setting are directly below that, with information about possible setting values.

Example

Let’s say we wanted to change the setting Require a Password on Wakeup to No within the High Performance power scheme. First, we need to use the output from POWERCFG -QUERY to find the associated GUIDs and setting index:

The output of POWERCFG -QUERY that highlights the GUIDs used in this example.

These values are then plugged into commands POWERCFG -SETACVALUEINDEX and POWERCFG -SETDCVALUEINDEX:

POWERCFG -SETACVALUEINDEX 8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c fea3413e-7e05-4911-9a71-700331f1c294 0e796bdb-100d-47d6-a2d5-f7d2daa51f51 0
POWERCFG -SETDCVALUEINDEX 8c5e7fda-e8bf-4a96-9a85-a6e23a8c635c fea3413e-7e05-4911-9a71-700331f1c294 0e796bdb-100d-47d6-a2d5-f7d2daa51f51 0

As you may have guessed, the first command affects the computer while it’s plugged in. The second affects the computer while on battery. There’s a few things that have been implied in this example, but are worth covering in case you plan to script power settings for a fleet of computers:

  • Windows includes three built-in power schemes: Balanced, High Performance, and Power Saver. These schemes are identified by the same GUID on every Windows 7 computer.
  • The GUIDs that identify subgroups and power settings are the same on every Windows 7 computer.
  • To create a new scheme, use this command: 
    POWERCFG -DUPLICATESCHEME <POWER SCHEME GUID> <NEW GUID>

    The <NEW GUID> parameter is optional. If it is not specified, POWERCFG will automatically generate a new GUID.

  • Remember that if <NEW GUID> is omitted, the GUID that identifies your new scheme will be different on each computer that you run this command on.
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categories Power Management, Scripting, System Administration, Windows 7 | tags , , ,

One Response to “Windows 7 Power Management: Applying Power Settings with POWERCFG”

  1. (iBoyd) » Windows 7 Power Management: Fixing PC Insomnia says:
    May 16, 2010 at 1:19 pm

    [...] you haven’t already, you should check out my previous article about power management in Windows 7 in order to learn about power profiles and POWERCFG.EXE [...]

    Reply

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