ACPI, which stands for Advanced Configuration and Power Interface is an open industry standard that was developed by many of the top computer companies such as HP, Intel, Microsoft, Phoenix and Toshiba. Perhaps the most notable part of ACPI is the power management element. It is also specified as the key element for OSPM (Operating System-directed configuration and Power Management).
The most imporant and commonly used aspect of ACPI is the power management. This type of power management will allow the operating system running on a computer to control the power. Prior to this standard, the power management was put into the hands of the computer’s BIOS, which meant that the operating system was unable to perform tasks such as physically turning off your computer once you have performed a shutdown. ACPI will allow the operating system to do this as well as many other aspects of the power savings such as turning off the monitor after a certain amount of time and turning off the hard disks when they have been inactive for a predetermined number of minutes.
Since the advent of ACPI, power saving features that were once only found in portable computers, have become commonplace on desktop computers and servers as well. Using these features, a computer may be put into a state in which very few devices are powered on, but can be quickly awaken in the case of an interupt such as the press of a keyboard button.
Because ACPI requires certain hardware in order to work properly, it cannot be added to older computers that have not been designed to support it. The first operating system that supported ACPI was Windows 98. This means that computers that came with older operating systems such as Windows 95, will not have the ability to follow the ACPI standard.
There are many different states used to define different situations in ACPI. There are global states that cover the different power states of the system as a whole. There are also device states that are specific to the various devices within the computer system, processor states specific to the computer’s CPU and performance states. More information on these states can be found online.
The ACPI standard does have some downfalls. First off, ACPI is a very complex standard compared to others. It is actually over 600 pages long and contains standards for many different componenets. The argument is that an ACPI compatible component is required to run very complex and potentially buggy code which could make a computer system unstable or insecure.
The other problem occurs when a device does not follow the ACPI standard, but claims to. When writing software for that device a decision will need to be made. It will either have to be written as ACPI compliant code, which could cause problems with the functionality of the the non-ACPI compliant device, or it can deactivate the ACPI standard to prevent the hardware issues with that device as a result of its non-compliance. This defeats the purpose of having an ACPI compliant device to begin with and does not give the manufacturer incentive to correct the issue as the device will work just fine with ACPI disabled software installed for it.
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