When hibernation is enabled in Windows 10, the operating system creates a file called hiberfil.sys in the root of your C: Drive. This hiberfil.sys stores the contents of memory (RAM) when you hibernate your PC. When you resume from hibernation, Windows reads this file again and transfers its contents back to memory. Because memory capacities on modern PCs are always increasing, the hibernation file takes up considerable disk space. Here is how you can compress the hibernation file and reduce its size in Windows 10.