C:\hiberfil.sys

C:\hiberfil.sys is a hidden system file and used by the Windows Kernel Power Manager to persist a copy of the system memory when hibernating a system. Thus, the size of the file is roughly equal to the amount of RAM installed on the computer.

On the command line, the file can be created or removed (and consequenctly hibernating be enabled or disabled) with the following commands (which require administrative privileges):

powercfg -h on
powercfg -h off