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Power Management is a feature of some electrical appliances, especially copiers, computers and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power state when inactive. In computing this is known as PC power management and is built around a standard called ACPI. This supersedes APM. All recent (consumer) computers have ACPI support.
In the military, ""Power Management"" often refers to suites of equipment which permit soldiers and squads to share diverse energy sources, powering often incompatible equipment. 
PC power management for computer systems is desired for many reasons, particularly:
- Reduce overall energy consumption
- Prolong battery life for portable and embedded systems
- Reduce cooling requirements
- Reduce noise
- Reduce operating costs for energy and cooling
Lower power consumption also means lower heat dissipation, which increases system stability, and less energy use, which saves money and reduces the impact on the environment.
Processor level techniques
The power management for microprocessors can be done over the whole processor, or in specific areas.
With dynamic voltage scaling and dynamic frequency scaling, the CPU core voltage, clock rate, or both, can be altered to decrease power consumption at the price of potentially lower performance. This is sometimes done in real time to optimize the power-performance tradeoff.
- AMD Cool'n'Quiet
- AMD PowerNow! 
- IBM EnergyScale 
- Intel SpeedStep
- Transmeta LongRun and LongRun2
- VIA LongHaul (PowerSaver)
Additionally, processors can selectively power off internal circuitry (power gating). For example:
- Newer Intel Core processors support ultra-fine power control over the functional units within the processors.
- AMD CoolCore technology get more efficient performance by dynamically activating or turning off parts of the processor.
Intel VRT technology split the chip into a 3.3V I/O section and a 2.9V core section. The lower core voltage reduces power consumption.
Operating system level: Hibernation
When a computer system hibernates it saves the contents of the RAM to disk and powers down the machine. On startup it reloads the data. This allows the system to be completely powered off while in hibernate mode. This requires a file the size of the installed RAM to be placed on the hard disk, potentially using up space even when not in hibernate mode. Hibernate mode is enabled by default in some versions of Windows and can be disabled in order to recover this disk space.
- CPU power dissipation
- Low-power electronics
- Dynamic voltage scaling
- Dynamic frequency scaling
- Advanced power management (APM)
- Advanced Configuration and Power Interface (ACPI)
- BatteryMAX (idle detection)
- 80 Plus
- Energy Star
- Green computing
- PowerTOP - diagnostic tool
- The Green Grid
- Sleep Proxy Service
- Standby power
- Thermal Design Power
- VESA Display Power Management Signaling (DPMS)
- Run-time estimation of system and sub-system level power consumption
- "Office of Naval Research - Power Management Kit". ONR. Retrieved 2015-01-15.
- "AMD PowerNow! Technology with optimized power management". AMD. Retrieved 2009-04-23.
- "IBM EnergyScale for POWER6 Processor-Based Systems". IBM. Retrieved 2009-04-23.
- "AMD Cool'n'Quiet Technology Overview". AMD. Retrieved 2009-04-23.
- Energy Star - Independent List of Products
- Energy Star - Low Carbon IT Campaign
- Energy Consumption Calculator
- Research Bibliography on Power Management