Reconfiguring the hardware while the system is in the S4 state might result in changes that prevent the hibernate file from loading correctly. If the hibernate file cannot be loaded, rebooting is required. System restarts from the saved hibernate file. Off, except for trickle current to the power button and similar devices. State S4 has the following characteristics: A computer in the hibernate state uses no power (with the possible exception of trickle current). 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. 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. Upon restart, the loader reads this file and jumps to the system's previous, prehibernation location. 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. To reduce power consumption to a minimum, the hardware powers off all devices. System power state S4, the hibernate state, is the lowest-powered sleeping state and has the longest wake-up latency. CPU context, cache contents, and chipset context are lost. Processor is off and some chips on the motherboard also might be off.Īfter the wake-up event, control starts from the processor's reset vector.

System power state S3 is a sleeping state with the following characteristics: Two seconds or more greater than or equal to the latency for S1.ĬPU context and system cache contents are lost.

Bus clocks are stopped some buses might lose power.Īfter wake-up, control starts from the processor's reset vector. Less consumption than in state S1 and greater than in S3. State S2 has the following characteristics: System power state S2 is similar to S1 except that the CPU context and contents of the system cache are lost because the processor loses power. Processor clock is off and bus clocks are stopped.Īll context retained and maintained by hardware. Less consumption than in S0 and greater than in the other sleep states. System power state S1 is a sleeping state with the following characteristics: Also see ADMINISTRATOR_POWER_POLICY structure. To restrict the system to a subset of Sx states, a user can provide MaxSleep and MinSleep fields in SYSTEM_POWER_POLICY structure. Typically, when the user presses the sleep button, the system goes to the S3 system power state. A user can specify the action to take when the sleep power button is pressed by using the Sleep button action. Use powercfg /a to enumerate all available sleep states on a system.

Furthermore, some devices might be able to wake the system only from S1 and not from deeper sleep states. For example, on some machines certain chips on the motherboard might lose power at S3, while on others such chips retain power until S4. All ACPI-compliant computers shut off their processor clocks at S1 and lose system hardware context at S4 (unless a hibernate file is written before shutdown), as listed in the sections below.ĭetails of the intermediate sleep states can vary depending on how the manufacturer has designed the machine. With each successive sleep state, from S1 to S4, more of the computer is shut down. In addition, on some computers, an external indicator tells the user that the system is merely sleeping. Some devices can wake the system from a sleeping state when certain events occur. The operating system need not be rebooted to return the computer to the working state. Unlike a system in the shutdown state (S5), however, a sleeping system retains memory state, either in RAM or on disk, as specified for each power state below in System hardware context sections. A system in one of these states is not performing any computational tasks and appears to be off. States S1, S2, S3, and S4 are the sleeping states.

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