Sleep & Hibernate are power-saving options in operating systems like Windows Vista & 7.
Sleep preserves whatever you were doing in memory while Hibernate writes your settings and the content of memory to the hard disk (to a hidden system file called Hiberfil.sys located in the root folder of the drive where the operating system is installed) and then completely powers down the system. The size of the Hiberfil.sys file is approximately equal to how much random access memory (RAM) is installed on the computer.
Hibernation is more power saving than Sleep but waking from a state of Hibernation takes longer than waking from Sleep.
Use the sleep mode you won’t be using the computer for a short time and the Hibernate mode when you are not going to use the computer for more than several hours.
To disable Hibernation, type powercfg.exe /hibernate off at the command prompt.