Sleep mode refers to a low power mode for electronic devices such as computers, televisions, and remote controlled devices. These modes save significant electrical consumption compared to leaving a device fully on and idle but allow the user to avoid having to reset programming codes or wait for a machine to reboot. Many devices signify this power mode by a pulsing led power light.
Sleep mode can go by many different names including stand-by (Windows), deep sleep (Mac) and suspend (Linux). When placed in this Sleep mode, aside from the RAM which is required to restore the machine's state, the computer attempts to cut power to all unneeded parts of the machine. Because of the large power savings, most laptops automatically enter this mode when the lid is closed.
Though generally thought as two separate functions, modern Macintoshes and some specially configured Linux machines also feature a variation of Sleep mode that incorporates the strengths of hibernate. The RAM is copied to the hard drive before sleep mode is initiated, allowing for safety from power failure and instant-on at the same time.
ACPI is the current standard for power management, superseding APM and providing the backbone for sleep and hibernation on modern computers. When a non-ACPI device is plugged in, Windows will sometimes disable stand-by functionality for the whole operating system. Without ACPI functionality, as seen on older hardware, sleep mode is usually restricted to turning off the monitor and spinning down the hard drive.
Stand-by mode may affect equipment lifetime. Stand-by mode may reduce the thermal cycles of key components, therefore possibly improving the equipment reliability. This means equipment might last longer, so less electronic equipment will be scrapped. On the other hand, equipment in standby mode is at increased risk of damage from power surges, so stand-by may also shorten equipment lifetimes.
Linux implementations of Sleep/Suspend/Hibernate