Hibernation

Hibernation is a state of inactivity and metabolic depression in endotherms. Hibernation refers to a season of heterothermy that is characterized by low body temperature, slow breathing and heart rate, and low metabolic rate. Although traditionally reserved for "deep" hibernators such as rodents, the term has been redefined to include animals such as bears and is now applied based on active metabolic suppression rather than based on absolute body temperature decline. Many experts believe that the processes of daily torpor and hibernation form a continuum and utilize similar mechanisms. Hibernation during the summer months is known as aestivation. Some reptile species (ectotherms) are said to brumate, or undergo brumation, but any possible similarities between brumation and hibernation are not firmly established. Some insects, such as the wasp Polistes exclamans, hibernate by aggregating together in groups in protected places called hibernacula.

Often associated with low temperatures, the function of hibernation is to conserve energy during a period when sufficient food is unavailable. To achieve this energy saving, an endotherm will first decrease its metabolic rate, which then results in a decreased body temperature. Hibernation may last several days, weeks, or months depending on the species, ambient temperature, time of year, and individual's body condition.

Hibernation (computing)

Hibernation (or suspend to disk) 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 before entering hibernation. Like a powered down system, the power source from a system in hibernation can be removed without any state loss risk.

Uses

Hibernation saves electrical power. After hibernating, the hardware is powered down like a regular shutdown. 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.

Comparison to sleep mode

Many systems also support a low-power sleep 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. Instantaneous resumption is one of the advantages of sleep mode over hibernation. A hibernated system must start up and read data back to RAM, which typically takes time. 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 power to keep the data in the RAM. Detaching power from a system in sleep mode results in data loss, while cutting the power of a system in hibernation has no risk; the hibernated system can resume when and if the power is restored. Both shut down and hibernated systems may consume standby power unless they are unplugged.