chapter 8 operating system
Hibernation (computing)
Hibernation in computing is powering down a computer while retaining its state.Upon hibernation, the computer saves the contents of its random access memory (RAM) to a hard disk or other non-volatile storage. Upon resumption, the computer is exactly as it was upon entering hibernation.
When used to save power, hibernation is similar to sleep mode and saves more power at the cost of slower resumption.
Uses of hibernation
Hibernation saves electrical power. After hibernating, the hardware is completely powered down (just like for a regular shutdown). Therefore a hibernated machine uses no more electrical power than one which is switched off. Meanwhile, hibernation is a means of avoiding the burden of saving unsaved data before shutting down and restoring all running programs after powering back on.Hibernation is used in laptops, which have limited battery power available. It can be set to happen automatically on a low battery alarm. Most desktops also support hibernation, mainly as a general energy saving measure.
sleep mode
Many systems also support a low-power sleep mode or stand by mode in which the processing functions of the machine are powered down, using a little power to preserve the contents of RAM and support waking up; wakeup is almost instantaneous.The advantage of sleep mode is that resuming is much quicker than for hibernation. A hibernated system must start up, then read back data to RAM on resuming, which typically takes about ten seconds or more. A system in sleep mode only needs to power up the CPU and display, which is almost instantaneous. On the other hand, a system in sleep mode still consumes some power, while a hibernated system does not require any power at all. A sleeping computer is a case of a device consuming standby power, covered by regulations in many countries limiting such power under the One Watt Initiative to one watt from 2010. Since these facilities were introduced, most systems have come to offer both sleep mode and hibernation.
