I was working on my old machine running Windows XP to connect to internet (it hasn't connected to internet for years), and when installing Windows Update, the disk space on C:\ drive seems almost full. Then I noticed there's file called hiberfil.sys (used by Windows when hibernate is enabled) that consumes almost half GB. I tried deleting the file from Windows Explorer but got access denied error. Finally, by running "powercfg -h off" from Command window, the file was deleted automatically by Windows and I got plenty free space :-)