ACPI FAQ
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· What is S3/Standby/Suspend to RAM and S4/Hibernate/Suspend to Disk?
S3/Standby is a "sleep state" (suspend to the system memory) that is supported by the systems hardware and certain operating systems. Once the system goes to sleep, it will "wake up" when the mouse is moved,any key is pressed on the keyboard or the power button is pressed .Auto Power-on & Shut-down can wake up the computer from standby or hibernation state at specified time. S4/Hibernate is a "sleep state" in which data is moved from system memory to the hard disk. This enables a system to 'wake' quickly while still helping to maintain data since you are not subject to power outages like you are when a system is in a screen saver mode, in S1 or in Standby (S3).
State Description
S0/Working System is on. The CPU is fully up and running; power conservation is on a per-device basis.
S1 Sleep System appears off. The CPU is stopped; RAM is refreshed; the system is running in a low power mode.
S2 Sleep System appears off. The CPU has no power; RAM is refreshed; the system is in a lower power mode than S1.
S3 Sleep (Standby) System appears off. The CPU has no power; RAM is in slow refresh; the power supply is in a reduced power mode. This mode is also referred to as 'Save To RAM'.
S4 Hibernate System appears off. The hardware is completely off, but system memory has been saved as a temporary file onto the harddisk. This mode is also referred to as 'Save To Disk'.
S5/Off System is off. The hardware is completely off, the operating system has shut down; nothing has been saved. Requires a complete reboot to return to the Working state.

· Which operating systems support Standby (S3) and Hibernate (S4)?
S3 an S4 are supported by Microsoft Windows 7, Windows Vista, Windows 2003, Windows XP, Windows 2000, Windows Me and Windows 98SE. Windows 95 and Windows NT do not support S3/4.

· What is the benefit of the Standby and Hibernate sleep mode?
When a user does not use the system , lets the system goes to "sleep" then will saving the furthest power. When the user is ready to use the system again, the system "wakes up" in a few seconds. When the system wakes up, it is at the exact point it was at when the system went to sleep. (for example: in the middle of a Word document) The S3/4 feature saves power and increases user efficiency (users do not have to wait for the system to shut down or re-boot).
· What about Security when the system is "always on"?
For security reasons, you can lock the system with the locking function of the Auto Power-on & Shut-down.
· How much power does my system use when the in S3/4 sleep state?
Many systems are designed to draw less than 15 watts of power in the S3 sleep state for any configuration. Many configurations will draw less than 5 watts. In the S4 state, the computer power consumption is equivalent to power off.
· How to wake up the computer from standby state?
Windows 98SE, Windows 2000, Windows XP, Windows 2003, Windows Vista and Windows 7 support wake up from the keyboard or power button but only Windows 2000 or above support wake up from the mouse.Auto Power-on & Shut-down support wake up the computer from standby state at specified time.
Wake event S1 state S3 state S4 state S5 state
Power button · · · ·
RTC alarm · · · ·
PME (LAN/Modem) PCI · · · ·
USB (KB, Mice) · 98, Me, 2K or above x x
Keyboard - PS2 · 98, Me, 2K or above x x
Mouse - PS2 · Me, 2K or above x x
Auto Power-on & Shut-down · · · x

· How many expenses can I save?
Electricity cost is calculated roughly with $0.07KWH , cost savings approximately $10-$50 1 year.