System Power State S4System power state S4, the hibernate state, is the lowest-powered sleeping state and has the longest wake-up latency. To reduce power consumption to a minimum, the hardware powers off all devices. Operating system context, however, is maintained in a hibernate file (an image of memory) that the system writes to disk before entering the S4 state. Upon restart, the loader reads this file and jumps to the system's previous, prehibernation location.
If a computer in state S1, S2, or S3 loses all AC or battery power, it loses system hardware context and therefore must reboot to return to S0. A computer in state S4, however, can restart from its previous location even after it loses battery or AC power because operating system context is retained in the hibernate file. A computer in the hibernate state uses no power (with the possible exception of trickle current).
State S4 has the following characteristics:
Power consumptionOff, except for trickle current to the power button and similar devices.
Software resumptionSystem restarts from the saved hibernate file. If the hibernate file cannot be loaded, rebooting is required. Reconfiguring the hardware while the system is in the S4 state might result in changes that prevent the hibernate file from loading correctly.
Hardware latencyLong and undefined. Only physical interaction returns the system to the working state. Such interaction might include the user pressing the ON switch or, if the appropriate hardware is present and wake-up is enabled, an incoming ring for the modem or activity on a LAN. The machine can also awaken from a resume timer if the hardware supports it.
System hardware contextNone retained in hardware. The system writes an image of memory in the hibernate file before powering down. When the operating system is loaded, it reads this file and jumps to its previous location.
System Shutdown State S5In the S5, or shutdown, state, the machine has no memory state and is not performing any computational tasks.
The only difference between states S4 and S5 is that the computer can restart from the hibernate file in state S4, while restarting from state S5 requires rebooting the system.
State S5 has the following characteristics:
Power consumptionOff, except for trickle current to devices such as the power button.
Software resumptionBoot is required upon awakening.
Hardware latencyLong and undefined. Only physical interaction, such as the user pressing the ON switch, returns the system to the working state. The BIOS can also awaken from a resume timer if the system is so configured.
System hardware contextNone retained.
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System Power States