Sleep mode

Sleep mode is a low power mode for electronic devices such as computers, televisions, and remote controlled devices. These modes save significantly on electrical consumption compared to leaving a device fully on and, upon resume, allow the user to avoid having to reissue instructions or to wait for a machine to reboot. Many devices signify this power mode with a pulsed or red colored LED power light.

In computers, entering a sleep state is roughly equivalent to "pausing" the state of the machine. When restored, the operation continues from the same point, having the same applications and files open.

Sleep mode has gone by various names, including Stand By (for Microsoft Windows 98-Server 2003), Sleep (for Mac OS 8-Mac OS X, Windows Vista, Windows 7, Windows 8, Windows 10, Windows Server 2008), Suspend (Windows 95) and Suspend to RAM (Linux). Machine state is held in RAM and, when placed in sleep mode, the computer cuts power to unneeded subsystems and places the RAM into a minimum power state, just sufficient to retain its data. Because of the large power saving, most laptops automatically enter this mode when the computer is running on batteries and the lid is closed. If undesired, the behavior can be altered in the operating system settings.

A computer must consume some energy while sleeping in order to power the RAM and to be able to respond to a wake-up event. A sleeping PC is a case of a machine on standby power, and this is covered by regulations in many countries, for example in the United States limiting such power under the One Watt Initiative, from 2010. In addition to a wake-up press of the power button, PCs can also respond to other wake cues, such as from keyboard and mouse.

Hibernation, also called Suspend to Disk on Linux, saves all computer operational data on the fixed disk before turning the computer off completely. On switching the computer back on, the computer is restored to its state prior to hibernation, with all programs and files open, and unsaved data intact. In contrast with standby mode, hibernation mode saves the computer's state on the hard disk, which requires no power to maintain, whereas standby mode saves the computer's state in RAM, which requires a small amount of power to maintain.

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