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System Standby (S3) v. Hibernation In New Windows PCs
Before understanding which mode of PC power management is best for a particular situation, it is important to have a basic understanding of the similarities and differences between System Standby and Hibernation in modern computers1.
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.
In general we recommend the application of system standby over hibernation for the following reasons.
These suggestions are based on recent standard PC configurations. For example, the table below summarizes measurements taken on a Dell Dimension 4400, Pentium 4.
Energy Savings Reduces power consumption from about 50 to 2.5 watts. Saving 47.5 watts. Reduces power consumption from about 50 to 1.8 watts. Saving 48.2 watts. Effectively no difference in energy savings potential between system standby and hibernate.
Response Time 5 - 10 seconds More than 20 seconds The response time for
hibernate depends on the amount of memory that was saved on the hard disk
during the shutdown procedure.
Saves work in the event of a power loss? No Yes System hibernate may be best applied to laptops that are running on batteries.
Response Mechanism Keyboard or mouse Power button With system standby users only need one mechanism (keyboard mouse) for both monitor and PC. Note: This may vary from brand to brand.
Typical Sleep Settings Less than 30 minutes to be qualified for ENERGY STAR. Greater than 60 minutes Shorter sleep settings means more energy savings.
The choice to enable System Standby, Hibernation or turning the system off is as much based on the situation the computer is used in as it is on power savings. Using the above information, one should be able to find a suitable method for their given situation. In most cases it is best to enable monitor power management at a period of 10 minutes, system standby at a time of 20 to 30 minutes. Hibernation should be employed at 60 minutes or higher if one wants their machine in a deep sleep for long periods of time and who is also concerned with start up times after long periods of being in the "off" state.