Sleep, Hibernation, and Stand By are the only true System Power States. Of the three, only hibernation provides no power to memory, and saves memory contents to the hard drive to be loaded back into memory when the computer wakes up.
Hibernation (also known as suspend to disk, or Safe Sleep on Macintosh computers) in computing is powering down a computer while retaining its state. When hibernation begins, the computer saves the contents of its random access memory (RAM) to a hard disk or other non-volatile storage. When the computer is turned on the RAM is restored and the computer is exactly as it was before entering hibernation. Hibernation was first implemented in 1992 and patented by Compaq Computer Corporation in Houston, Texas. Microsoft's Windows 10 employs a type of hibernation (fast startup) by default when shutting down.