Many of us hibernate our PCs instead of turning them off. This provides a quick way to restart while using less power than the “Sleep” mode. This is particularly useful in laptops. Hibernation works by placing the contents of RAM in a hidden system file called “hiberfil.sys”. In Windows XP and Vista, this file is the same size as the amount of RAM that is installed on the PC. In Windows 7, the default is 75% of the RAM size. This file is always in the root of the drive with the Windows folder or normally the C: drive.
Deleting and restoring hiberfil.sys
It has become common to have a rather small volume for the C: system drive. It has also become common to have 4GB or more of RAM. This means that hiberfil.sys can take up a substantial portion of your system drive. If drive space becomes critical, you may wish to delete the hiberfil.sys file and turn off hibernation. Because hiberfil.sys is a super-hidden system file, the usual way to delete a file does not apply. However, there is a very simple way that uses the command line run as administrator.
Open a command prompt run as administrator and enter
powercfg –h off
That’s all there is to it. To restore the file enter
powercfg –h on
These changes take place right away
The command-line method is also useful for dealing with a corrupt or badly fragmented hiberfil.sys file. In the process of going in and out of hibernation many times, the file sometimes becomes corrupted. Deleting the file and then restoring it will clean up the file.
Changing the size of hiberfil.sys
If you wish to retain hibernation but want to reduce the size of hiberfil.sys, that can also be done in the command line. The file can be reduced to a smaller percentage of RAM with the command "powercfg –h -size <percent size>”. The command must be run as administrator. For example, to reduce hiberfil.sys to 50% of installed RAM, use
powercfg –h -size 50
Percent size cannot be smaller than 50.
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