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Concept
Power management
Summary
Power management is a feature of some electrical appliances, especially copiers, computers, computer CPUs, computer GPUs 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 computers have ACPI support.
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.
The power management for microprocessors can be done over the whole processor, or in specific components, such as cache memory and main memory.
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.
Examples:
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.
ARM's big.LITTLE architecture can migrate processes between faster "big" cores and more power efficient "LITTLE" cores.
Hibernation (computing)
When a computer system hibernates it saves the contents of the RAM to disk and powers down the machine.
Official source
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