Sleep mode

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 boot.

Because of the large power saving, most laptops automatically enter this mode when the computer is running on batteries and the lid is closed.

In addition to a wake-up press of the power button, PCs can also respond to other wake cues, such as from keyboard, mouse, incoming telephone call on a modem, or local area network signal.

Without ACPI functionality, as seen on older hardware, sleep mode is usually restricted to turning off the monitor and spinning down the hard drive.

Microsoft Windows 2000 and later support sleep at the operating system level (ACPI S3 state) without special drivers from the hardware manufacturer, except of video adapters.

In older versions prior to Windows Vista, sleep mode was under-used in business environments as it was difficult to enable organization-wide without resorting to third-party software.

[4] A variety of third-party PC power management software exists for newer versions of Windows, offering features beyond those built into the operating system.

Since Safe Sleep also allowed state to be restored in an event of a power outage, unlike other operating systems, hibernate was never offered as an option.

The feature saves the contents of volatile memory to the system hard disk each time the Mac enters Sleep mode.

[9] Safe Sleep capability is found in Mac models starting with the October 2005 revision of the PowerBook G4 (Double-Layer SD[vague]).

If the computer being awakened is communicating via Wi-Fi, a supplementary standard called Wake on Wireless LAN (WoWLAN) must be employed.