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Checking Laptop Power Usage in Windows 7

written by: Lamar Stonecypher•edited by: Rebecca Scudder•updated: 11/21/2011

Windows 7 was intended to improve battery performance and decrease system overhead in several different ways that benefit laptop users. Here we'll look at how it works and how to get a detailed report of the system's current power status, as well as possible suggestions for improvement.

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    Changes since Vista

    • The command-line "powercfg.exe" tool has been given a new switch called "-energy" in Windows 7. When that's selected, it does a sixty-second scan of the system and then writes the results to a HTML file for review. This tool gives some very specific suggestions.
    • Fewer drivers are loaded at start-up, and Windows 7 tries to load drivers "in tandem" or at the same time. Fewer processes run in the background, and some defer loading until they are actually needed. Microsoft calls this just in time loading "Trigger-Start." It is part of a deliberate effort ito have the CPU return to and remain at an idle state as often as possible. In fact, Microsoft says that optimizing for the processor state is more important than optimizing for memory or hard drive storage because the CPU operates over such a wide range of speeds, utilization, and power consumption.
    • Windows 7 also tries to avoid increasing the processor speed except when it's absolutely required.
    • Microsoft has also worked on (standard definition) DVD playback, and they derived some dividends there. Playback in Windows 7 uses fewer resources than Windows Vista in CPU and graphics, audio playback, and DVD read efficiency.
    • Windows 7 keeps a closer watch over USB devices and tries to create a “selective suspend." One example of a USB device that benefits from more active management is a finger-print reader.
    • Windows 7 attempts to intelligently manage the screen brightness, which by the way, is responsible for about 40% of the total power utilization on a laptop. Dimming the screen is the most effective single method for prolonging runtime.
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    Sleep vs Hybrid Sleep vs Hibernate

    I have previously written about “Is Using Vista’s Hybrid Sleep Safe for My Laptop?" and concluded that for most folks, it was both safe and power efficient. That is still true in Windows 7, but Windows 7 does not give us any better fine-grained control over when the laptop in hybrid sleep mode will switch to hibernation and shut down. Many laptop users would prefer to have it happen sooner rather than later, of course, in order to preserve the battery.

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    Microsoft has come up with some interesting research in this area. A laptop that is sleeping with power applied only to maintain what’s actively in RAM will typically draw 1 watt or less from the battery. The laptop will also resume in as little as two seconds from this state.

    A laptop that is hibernated has written its memory contents to the hard drive and has shut down.The power draw is the same as having the device switched off, but the time to restart depends on the size of RAM installed and how long it takes to load the memory contents from the hard drive.

    Hybrid sleep is a combination of sleep and hibernation. When the device is put to sleep, it writes the data to the hibernation file and then continues to keep the memory powered – for a while. If the user does not interact with the computer again within a certain time, hybrid sleep will allow the device to go into hibernation.

    Shut down, of course, simply turns off the laptop, and the next restart is a regular boot-up from the hard drive.

    In general, I think it’s makes the most sense to use hybrid sleep when (1) you know that you’ll likely be using the laptop again within an hour or so, and (2) when you’re uncertain that you’ll be back that quickly, but you’re sure it won’t be more than four or six hours.If longer than that, you can prevent the small drain that hybrid sleep provides by hibernating the laptop instead.

    Finally, the type of sleep mode to choose should be influenced by your desired battery management. For example, my notebook is normally plugged in, and I have it set to recharge only when it drops below 88% capacity. It normally floats around the 90 to 96% mark when used at home, and this avoids unnecessary, unhelpful battery cycles. I routinely hibernate this machine except when I know that I’ll be using it again within an hour or so.

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    Power Configuration Switch in Windows 7 powercfg.exe

    A “switch" is a modifier that comes after a program name in Windows. It is usually set apart by a dash or a forward slash. Here is an example of the command and switch we’ll use to get a detailed listing of our laptop’s power configuration settings.

    powercfg -energy

    In order to run the query, start at the Windows start button/orb and select “All Programs." Then choose “Accessories" and right-click “Command prompt." Next, click “Run as administrator." You’ll need to clear the command prompt if UAC is at a high setting. Then type in the command above and press Enter.

    The scan will take 60 seconds, and then it will rapidly scroll the screen displaying the results. Don’t worry about this because it also writes the results to a file called “energy-report.html."

    When the scan completes, click on “Computer" and navigate to C: Drive → Windows → System32. There type

    energy-r

    in the search bar at top-right. It should quickly locate the energy-report.html file in the folder and select it. Grab it and drag it out to your desktop. Once there, double-click it and it will open in your web browser.

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    When I ran the scan with my laptop at idle, powercfg showed:

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    It did not take long upon looking at the outputted HTML file to determine that the powercfg program was concerned about something that I was not – the efficiency settings of the entire laptop, including when it is plugged in. It never had occurred to me that my (elderly) workstation-class notebook should run at anything less than “giddy-up" when used on my desktop. When plugged in, maximum performance to me means speed and power. The picture changes, however, when it’s off the cord. Then I think that maximum performance is battery endurance, at least enough to let me watch a DVD on a plane. (Of course, I really mean getting some work done during the flight.)

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    The first section showed information about the laptop.

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    The errors, which were deemed more serious and which had a red background, were mostly about settings with the laptop plugged in.

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    This was a bit puzzling to me as one would think that the settings on battery would be just as important.

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    I had previously selected the "Balanced" power plan on the notebook as it seemed very reasonable and I was not planning any trips away from plugs. The items that it flagged for warnings and their suggested settings were:

    • Display timeout is long on battery (over 15 minutes)
    • Display dim is long on battery (over 5 minutes)
    • Sleep timeout is long on battery (over 30 minutes)

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    It also chided that the wireless settings were adjusted for maximum performance (plugged in) and found that the processor utilization was "moderate" at 3.06%. It listed three applications running: Kaspersky Antivirus was at 0.87%, svchost.exe at 0.28%, and another process I didn't recognize also at 0.28%.

    There was more information about the battery, sleep modes supported, display brightness adjustability, processor management, and battery type and condition.

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    There you have it - how to get a detailed laptop power usage report in Windows 7.

    This is all good information, and having this new ability in an old utility is handy and actually useful. It's too bad that they haven't created a user interface for powercfg.exe and turned it into a more user-friendly application. Then again, it's not something that one needs to look at frequently.

References

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