Aggressive Link Power Management Explained

Aggressive Link Power Management (ALPM) is a power management protocol for Advanced Host Controller Interface-compliant (AHCI) Serial ATA (SATA) devices, such as hard disk drives and solid-state drives.^[1]

Description

When enabled via the AHCI controller, this allows the SATA host bus adapter to enter a low-power state during periods of inactivity, thus saving energy. The drawback to this is increased periodic latency as the drive must be re-activated and brought back on-line before it can be used, and this will often appear as a delay to the end-user.

States

There are three states:^[2]

• Active
• Low Power with two internal states Partial and Slumber. Partial has a maximum return latency of 10 microseconds while slumber has a maximum latency of 10 milliseconds. The states can be initiated by Host (HIPM), Device (DIPM) or both. Hot swapping is disabled.
• Device Sleep with a maximum return latency of 20 milliseconds unless otherwise specified in Identify Data Log

These can be selected by the SATA AHCI driver, usually via a configuration option, or by the OS Power Options. Windows Vista and later allows the tweaking of AHCI LPM modes through a registry hack.^[3] Hot swapping is disabled.

See also

• Energy Star
• Green computing
• Active State Power Management (ASPM)

External links

• Aggressive Link Power Management - Red Hat
• Web site: Designing Energy Efficient SATA Devices. - Intel

Notes and References

1. Web site: Serial ATA AHCI: Specification, Rev. 1.3. Intel. 31 October 2012.
2. Web site: Designing Energy Efficient SATA Devices. Intel. 31 October 2012.
3. Web site: Add AHCI Link Power Management to Power Options in Windows. 26 July 2017. 4 January 2023.