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advanced configuration and power interface (power management) (ACPI)

Advanced Configuration and Power Interface (ACPI) is an interface for power management in personalcomputers. With ACPI, which was specified in 1997, the power-saving functions are executed by the operating system and not by the BIOS. In order for the connected devices to be controlled, they must be ACPI-enabled. They can then be individually put into sleep and hibernation mode and reactivated again by software, depending on requirements. However, this requires the Windows Driver Module(WDM) as a device driver under Windows.

ACPI is an open standard, developed by Intel, Toshiba and Microsoft, which has already been revised several times. It differentiates between several energy-saving functions, such as hibernation, the idle state with standby mode, in which essential hardware components, such as the hard disks and the display, are switched off, but the working memory continues to be buffered, the sleep state or the On-Now function, in which it is switched directly from the economy mode to the application programs without reloading.

ACPI power modes

ACPI power modes

The main ACPI modes are Suspend to RAM( STR), which is referred to as S3 mode, S1 mode Suspend to Disk( STD), Hibernation is S4 mode and Soft-Off state is S5 mode.

Hibernation activated during shutdown under Windows XP

Hibernation activated during shutdown under Windows XP

In S3 standby mode, the entire content is stored in the RAM and in S1 mode on the hard disk. The energy consumption only differs by half a watt or a bit more in these two modes, but this cumulates to several kilowatts over a year. The soft-off mode S5 prescribes a consumption of only 2 W in this mode in 2010, in 2014 the limit is only 1 W. ACPI controls the brightness and color temperature of displays depending on the ambient light with another energy-saving function. This function is controlled by an Ambient Light Sensor( ALS) and always adjusts the brightness of the display to the ambient light.

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Englisch: advanced configuration and power interface (power management) - ACPI
Updated at: 20.03.2013
#Words: 306
Links: interface (I/F), power management (PM), operating system (OS), basic input/output system (BIOS), indium (In)
Translations: DE
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