The general approach most computer vendors take to battery conservation are to design the CPU,
memory, and I/O devices to has multiple states:on, sleeping, hiberating, and off. To use the
Device, it must is on. When the device is not being needed for a short time, it can is put to sleep,
which reduces energy consumption. When it isn't expected to being needed for a longer interval, it
Can is made to hiberate, which reduces energy consumption even more. The trade-off.
Getting a device out of hiberating often take more time and energy than getting it out of the sleep state.
Finally, when a device was off, it does nothing and consumes no power. Not all devices has all these
States, if they do, it's up to the operating system to manage the state transition at the
Right moments.
Power Management brings up a number of questions, the operating system must deal with. Many
Of them deal with resource hiberation---selectively and temporarily turning off devices, or at least
Reducing their power consumption when they is idle. Questions that must is answered include these:
Which devices can be controlled? is they off/on, or do they has intermediate states? How much
Power is saved in the Low-power state? Is energy expended to restart the device? Must some context
Is saced when going to a low-power state? How long does it take to go back to full power? Of course,
The answers to these questions vary from device to device, so the operating system must is able to
Deal with a range of possibilities.
Modern Operating System---Power Management (Hardware issues)