ACPI States

ACPI (Advanced Configuration and Power Interface)

ACPI (Advanced Configuration and Power Interface) is an industry standard for managing power and hardware configurations in modern computer systems. It was developed to standardize and simplify the control of power consumption and hardware configurations by providing a uniform interface between the operating system and the hardware. With ACPI, operating systems can dynamically change power consumption and hardware configurations to adapt to the system's needs and optimize power consumption. For example, operating systems with ACPI support can reduce the power consumption of CPUs and other hardware when they are not in full load operation to minimize the overall energy consumption of the system. In addition to power management, the standard also takes care of the hot-plugging capability of certain hardware components such as hard disks, network cards and USB devices and helps the operating system to recognize and configure newly connected hardware. In short, ACPI is the standardized connection between the operating system and the hardware (and BIOS).

ACPI Sleep States

ACPI Sleep States are states in which the computer is put into a lower power consumption mode when it is not in use. The main purpose of the ACPI Sleep States is to save energy and extend the life of the hardware. There are different sleep states that save energy at different levels.

Detailed explanation

State S0

This is the fully active state in which the computer is operated normally.

State S1

In this state, the processor is put into standby mode, but the RAM remains active. This is the first sleep state the computer enters when you put it to sleep.

State S2

In this state, the processor is put into standby mode and the RAM is shut down. The computer takes a little longer to wake up from this state because the RAM has to be started up again.

State S3

This is the deepest sleep state, in which the processor, RAM and all other hardware components are shut down. The computer takes a little longer to wake up from this state because all hardware components have to be started up again.

State S4

S4: This is the "Hibernate" state, in which the computer saves all current data to the hard disk and then shuts down. When the computer is started from this state, all data is loaded back into RAM and the computer starts at the point where it was turned off. This sleep state consumes almost no energy, but the computer takes longer to wake up because all data has to be loaded from the hard disk.

State S5

S5: This is the "Power-off" state, in which the computer is completely turned off. In this state, the computer consumes no energy and cannot be started without the power being turned on again.

ACPI Device States

The ACPI Device States are states in which individual hardware components can be put into a lower power consumption mode when they are not in use. These states can save energy at different levels and help to extend the life of the hardware.

Device State D0

This is the fully active state in which the hardware is operated normally.

Device State D1

In this state, the hardware is put into a lower power consumption mode, but remains functional. The power consumption is higher than in the deeper device states, but the transition to this state is faster.

Device State D2

In this state, the hardware is put into a deeper power consumption mode. The power consumption is lower than in the D1 state, but the transition to this state takes longer.

Device State D3

This is the deepest device state in which the hardware is completely shut down. The power consumption is the lowest, but the transition to this state takes the longest.

Device State D4

This state is similar to the D3 state, but the transition to this state is faster. The power consumption is still very low, but the transition takes less time than in the D3 state.

Device State D5

This state is similar to the D2 state, but the transition to this state is faster. The power consumption is still lower than in the D1 state, but the transition takes less time than in the D2 state.

Reading out the supported states under Linux

Under Linux, the supported ACPI states can be read out via the sysFS. First of all, you need the path of the device, which can be output with the command lspci -v. As soon as the path for the corresponding device is known, you can use cat to display the supported device states.

Here is an example:

cat /sys/devices/pci0000:00/0000:00:1c.0/0000:02:00.0/power_state

Further information about the power management of the device can be found in the file power_management :

cat /sys/devices/pci0000:00/0000:00:1c.0/0000:02:00.0/power_management