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Using Sleep or Hibernation to Save Battery Power

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This document pertains to HP Notebook PCs with Windows Vista
You're in the middle of a project, you need to take a break, but you don't want to shut your computer down completely. You can put your computer into sleep or hibernation to conserve your battery power and yet not have to completely restart Windows after your break.
Window provides three simple options that allow you to enter one of these power-saving modes and to return to fully operational without have to restart your computer. The options are:
  • Pressing the power button
  • Pressing the sleep button
  • Closing the lid
Windows sets defaults, but it also allows you to change what power-saving state each action enters. Sleep and hibernation provides options between being fully-powered on or completely shut down. Without these modes, every time you need to conserve you battery, you would have to shut down and then endure the entire Windows boot process. Both sleep and hibernation are designed to save battery power when the computer is idle and allow a quicker return to functionality. Windows also recommends you to set a password to prevent another person from being able to "wake up" the computer and have access to your data.

What is sleep?

By default, Windows puts your computer to sleep when you press the power button on your computer. This applies both to the physical power button and to its software counterpart, which you can find when clicking start. You can also click Start and the arrow button for a list of additional options. Sleep automatically preserves your open documents and programs in memory and shuts down all nonessential functions.
Figure 1: Software Power Button
The main advantage of sleep is that it takes only seconds to restore your computer to where you left off—and uses only about as much electricity as a night light.
The disadvantage is that sleep mode retains the power to your memory (RAM). Thus, there is no saving of the memory contents to a file and which means no reloading of memory which makes it faster. However, if there is a power interruption for some reason while in this state, all your unsaved memory content is lost.

What is hibernation?

Hibernation is a deeper “off state” than sleep, and thus offers greater power savings at the cost of a slightly longer reboot time. It is also safer, because, unlike sleep, hibernation not only shuts down the power to peripherals (monitor, etc.) and hard drives, but also turns off the power to the RAM memory chips.
Hibernation saves (writes) all data in memory to a reference file on your hard drive before removing power. It then returns (reads) this file and reloads the data back into memory when you come out of hibernation. Thus restoring you to where you were before. The saving of memory data is why it takes a little longer to return (wake) from hibernation than coming out of sleep.
NOTE:However, if you want to power down your computer completely click the arrow next to the Lock button and then click Shut Down. This option also closes any open programs (you'll have the opportunity to save your work), shuts down Windows, and powers down your computer.

How do I configure my sleep and hibernation settings?

If you prefer to have Windows place your computer into another mode instead of sleep, you can change the power saving default settings. Windows provides the option to define your power buttons and the option to turn on password protection on exiting.
  1. Click Start , Control Panel, System and Maintenance, and then click Power Options.
  2. From the Select a power plan page, click Choose what the power buttons do from the list on the left panel.
  3. On the Define power buttons and turn on password protection page, you then have the option of choosing what happens when you:
    • press the power button
    • press the sleep button
    • close the lid
      Figure 2: Power Button Options
  4. For each of the above options, you can choose the what action occurs when the computer is either On battery or Plugged in. Click the down arrow on the button and choose one of the following options:
    • Do nothing
    • Sleep
    • Hibernate
    • Shut down
  5. Click Save changes.
  6. You can also choose to require a password upon wake up by selecting Require a password (recommended). However, any time the computer goes into a power saving mode you will have to enter your password to continue.
  7. Click Save changes to complete your selections .

How do I exit the power-saver modes

When the computer enters into hibernate or sleep, the Power button or LED blinks. To resume, press the Power button again and the computer should return to the same condition it was in before it went into hibernation or sleep.
NOTE:If you are using a screen saver and the On resume, display logon screen box is selected, you will have to enter your password even if you do not normally require a password when exiting sleep or hibernate.

Fixing devices that don't work after resuming from hibernation

If you were using a device such as your webcam when you put your computer into sleep or hibernate mode, the device may not function when you exit the power saving mode. If you experience this, you should ensure that your BIOS is the latest available for your computer. If your BIOS is current, then ensure your drivers are up to date. If a later version of the BIOS or a device driver is available, then download and install the update.

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