Monday, February 15, 2010

system standby VS hibernate


system standby is a hardware/software solution where the hardware and software work together to manage the computer's power usage by shutting down some non-critical systems (Fans, drives, peripherals) and throttling back the critical ones (CPU, Network). Hibernation is a Software only solution that basically takes the current snapshot of the system (RAM memory) and writes it to the hard disk then informs the hardware that it should do a complete shutdown. When the hardware is turned back on, the hardware does a full POST (Power On/Self Test) process and then passes off to the software to do a full boot. Since the software wrote a copy of itself to the hard drive it skips it's full boot process and simply loads the system snapshot written to disk back into RAM and the applications that were running generally have no idea they were not running during that period of time the machine was "off". In short, Hibernation was created to give the false impression of quick "boot" times for users who wanted to start up their computers faster.
All of this seems to suggest that Hibernation would save more energy than System Standby. Although more will be said later on with regards to the subject, it is important to understand how modern PC hardware is designed. In the "old" days2 the power switch was hardwired to the power supply and when the switch was off then the power supply was off and little3 energy was being consumed. In modern configurations4 the power supply is always drawing some energy and supplying the system's motherboard with a trickle current. The motherboard uses this to keep an idea of what state the hardware is in ("on" or "off") and manage the devices accordingly. When a user switches "on" the power button, the motherboard5 determines what state it should change to based on rules. In a two state system the most basic is what state is the hardware in now and then change to the opposite state. As such, Hibernation, System Standby and turning a system "off" will result in similar if not the same power draws.

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