Sleep saves any open documents and programs to RAM, switches off everything else, and then places the computer in a low-power state (commonly known as standby-mode), for this reason the computer can ‘wake-up’ very quickly. In Sleep mode, the power load is reduced considerably, saving a lot of energy. However, the power must not be cut off, and must be continue to supply to the computer. If you lose power while in sleep state, all current data will be lost since RAM is what we call volatile memory, so if a PC loses power, RAM loses the information it has stored in it.

Hibernation saves any open documents and programs to a hard drive before removing power from the computer. When computer is turned back on the running programs are reloaded from the file stored on hard drive so it appears they were never exit. The PC consumes even less power when it’s switched to hibernate. In fact, during hibernation, no power at all is used; you could technically leave the computer in this state for years. The main disadvantage of hibernation is that the computer takes longer to switch itself back to working state than it would from ‘sleep’.

 Both ‘sleep’ and ‘hibernate’ are power saving features that provide an easy and quick way to leave your computer in existing last state and come back to work on it at exactly the same state later without waiting too long to system to restore itself.