Like Windows XP, you can put Windows Vista in hibernate mode too. When you hibernate Windows Vista, your computer saves all contents of the RAM in a file called hiberfil.sys in the root folder of the system partition. This file is same in size as the size of the RAM memory you have in your system. If you have 4 GB RAM, then this file is also 4 GB in size. If you do not use hibernation feature of Windows Vista, then this file is consuming a lot of disk space on your hard disk. If you do not use hibernation feature, you can turn it off and claim the disk space taken by hiberfil.sys.
Turn off hibernation
To turn off hibernation, open an elevated command prompt window as discussed in this article : How to open an elevated command prompt. In the command prompt window, type powercfg -H OFF and press Enter to turn off hibernation. It would automatically remove the hiberfil.sys file in the root folder of your system drive.
Turn on hibernation
To turn on hibernation, open an elevated command prompt window as discussed in this article : How to open an elevated command prompt. In the command prompt window, type powercfg -H ON and press Enter to turn on hibernation. It would automatically create the hiberfil.sys file in the root folder of your system drive.