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Shutdown, Hibernate or Sleep?

PowerMAN offers three levels of power saving. The following explanation may be useful when determining which strategy to use:

  • Shutdown (Power Off) – The most efficient (and extreme!) method of power saving. This is generally only appropriate for situations where no user is logged on. Some sites, such as public access areas, may consider this policy for logged on users after a warning period to deter users from leaving computers unattended. Any programs or open documents are closed and the user must re-open them again before continuing.
  • Hibernate (S4) – This consumes the same amount of power as shutdown but allows the user session to be restored with a short delay (usually about 30 seconds). Any programs or open documents are preserved and the user may continue immediately after the system has resumed. This is appropriate for computers which are used long-term by the same user and where it would be inconvenient to shutdown the PC. Typically this policy would be used in an office environment.
  • Sleep (S1-S3) – This consumes more power than hibernate but allows the user to become active again within a few seconds. Any programs or open documents are preserved and the user may continue immediately after the system has resumed. Typically a PC in this state consumes only 2% of the energy used when running normally. However, this depends upon the exact configuration of the hardware (usually in the system BIOS).
Hibernate and sleep do not log out the current user and after entering their password. The user may continue immediately with their work. In some shared computer situations, such as a public access area, this can be inappropriate because the workstation will be locked for a subsequent user. In this situation PowerMAN may be used to log the user out before entering the low power mode.

In order of increasing energy consumption the available states are as follows:

  • S1 Sleep Smallest energy saving. System appears off but still requires a power supply. The CPU is stopped; RAM is refreshed; the system is running in a low power mode.
  • S2 Sleep System appears off but still requires a power supply. The CPU has no power; RAM is refreshed; the system is in a lower power mode than S1. Hardware support for this intermediate mode is quite rare.
  • S3 Sleep Bigger energy saving. System appears off but still requires a power supply. The CPU has no power; RAM is in slow refresh; the power supply is in a reduced power mode. This mode is also sometimes referred to as 'Save To RAM'. This mode is more common than S1.
  • S4 Hibernate Biggest energy saving. The system is actually off and may be unplugged or transported.
  • S5 Shutdown Same as hibernate.
Please remember that not all states are available on all hardware. The PowerMAN site reporting tool can be used to find which states are available on each PC. As a general rule PowerMAN will use the most energy efficient state supported by the hardware.