Editing Advanced Power Management (section)

==Overview==
[[File:APM-Layers.svg|thumb|The layers in APM]]
APM uses a layered approach to manage devices. APM-aware applications (which include device drivers) talk to an OS-specific APM driver. This driver communicates to the APM-aware BIOS, which controls the hardware. There is the ability to opt out of APM control on a device-by-device basis, which can be used if a driver wants to communicate directly with a hardware device.

Communication occurs both ways; power management events are sent from the BIOS to the APM driver, and the APM driver sends information and requests to the BIOS via function calls. In this way the APM driver is an intermediary between the BIOS and the operating system.

Power management happens in two ways; through the above-mentioned function calls from the APM driver to the BIOS requesting power state changes, and automatically based on device activity.

In APM 1.0 and APM 1.1, power management is almost fully controlled by the BIOS. In APM 1.2, the operating system can control PM time (e.g. suspend timeout).

In 1997, [[Phoenix Technologies]] released "APM 2.0" which is a kernel [[device driver]] compatible with an APM 1.2 BIOS.<ref>{{Cite news |title=APM 2.0: BIOS independent power management under Windows NT 4.0 or 3.51 |url=http://www.award.com:80/resources/apm-portables-ds.zip |url-status=dead |archive-url=https://web.archive.org/web/20051109023014/http://www.award.com:80/resources/apm-portables-ds.zip |archive-date=2005-11-09 |work=[[Phoenix Technologies]]}}</ref>