power management

Power management is a feature of some electrical appliances, especially copiers and computer peripherals such as monitors and printers, that turns off the power or switches the system to a low-power state after a period of inactivity. One power management standard for computers is ACPI, which supersedes APM. All recent (consumer) computers have ACPI support.

Motivations

Power management for computer systems are desired for many reasons, particularly:

• For portable and embedded systems: to prolong battery life and reduce heat dissipation requirements.
• For desktop systems: reduce cooling requirement and reduce noise.
• For supercomputers: reduce operating costs from energy and cooling.

Lower power consumption also means low heat dissipation, which increases system stability, and less energy use, which saves money and reduces the burden on the environment.

Processor level techniques

The power management for microprocessors could be done over the whole processors or some fine-grain areas.

For global power control, there are:

• Dynamic Voltage and Frequency Scaling (DVFS: an energy-saving technique that consists of varying the frequency and voltage of a microprocessor in realtime according to processing needs.
• Intel SpeedStep, AMD Cool'n'Quiet, AMD PowerNow!, VIA PowerSaver: allows the clock speed of a processor to be dynamically changed depending on workload levels.

Newer Intel Core processors support ultra-fine power control over the function units within the processors.

Operating system level: Hibernation

Main article: Hibernate (OS feature)

When computer system hibernates it dumps the entire contents of the RAM to disk and powers down the entire machine. On startup it reloads the data. It 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, 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.

See also

• DVFS Dynamic Voltage and Frequency Scaling for processors.
• Advanced Power Management (APM)
• Advanced Configuration and Power Interface (ACPI)
• VESA Display Power Management Signaling (DPMS)
• Energy Star
• Hibernate
• Green computing and Green energy

External links

• Energy Consumption Calculator
• Research Bibliography on Power Management

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