Advanced Configuration & Power Interface (ACPI)

(For Geeks Only)
By Joe Callison
6 August 2022

Advanced Configuration & Power Interface (ACPI)

The Windows operating system ACPI standard can support several states of power for computers, but not all are typically supported by the hardware manufacturer. The possible states are identified as follows: 

S0: normal working state

S1: CPU stops executing instructions but is still powered

S2: CPU loses power, but other components are still powered

S3: Most PC components lose power but RAM is kept refreshed in a low power state. This is the most common state that is defined as the “sleep” or standby state in Windows.

S4: This is the “Hibernate” state and is one of the items that can be configured after clicking “Change settings that are currently unavailable” in the Control Panel settings under Power Options – Choose what the power button does – Define power buttons and turn on password protection, as shown below (blue text next to the shield). Current system data and memory is written to a storage file (hiberfil.sys) and then all system power except for the network adapter, keyboard, mouse, and USB devices is lost. This is defined as the “hibernate” state in Windows. Waking from hibernation through one of the powered devices will reload the system data and memory from storage.

S5: This is the “shutdown” state in Windows. All system power is shut down in an orderly sequence.

G3: This is the hardware shutdown that functions outside of Windows to shut down all system power. The hardware power button can be configured in the Windows settings to initiate sleep, hibernate, shutdown, turn off the display, or nothing with a brief press. Depressing the power button for approximately 4 seconds or longer will turn off the power without going through a soft shutdown sequence.

There are additional power-related states that are variations of these states.

Low Power Idle (Standby) is an S0 state supported on some devices such as phones and tablets to conserve the battery and wake quickly.

Hybrid Sleep is an S3 state that will write to a hibernation storage file in the event power is lost while in the sleep mode. This is only provided on some devices by manufacturers.

Fast Startup writes to a hibernation storage file during a normal shutdown after the user is logged off, so only the operating system data is restored from storage, to speed up the boot process. This is a Windows feature that can be enabled or disabled in the Windows settings. The “restart” in Windows does not write to a hibernation file when shutting down regardless of the fast startup setting.

The available power states and their configuration status can be shown using the command prompt as follows:

Open Start

Right-click on Command Prompt and select the Run as administrator option

Type powercfg /availablesleepstates or powercfg /a and press Enter

The Hibernate state can be turned on or off from the command prompt. For example, powercfg /h on will turn hibernation on, and powercfg /h off will turn hibernation off. If hibernation is turned off, this will also disable Hybrid Sleep and Fast Startup from writing a hibernation file, it appears from the command prompt report below.

Other powercfg commands can be explored using help by entering the following in the command prompt:

powercfg /?

Posted by Joe Callison

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