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Appendix B: Power / Sleep / Global states explained

Under Advanced Configuration and Power Interface (ACPI) specification a PC can be in one of

several Power states. These power states are also known as Sleep (Sx) states or Global (Gx) states.

S0 is the ON state. The PC is fully functioning. All system devices and operating system, if

available, are running. S0 is also known as G0.

S3 is the Standby (Microsoft terminology) or Suspend-to-RAM state. The memory subsystem and

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power rail remains powered, while the rest of the system including the processor are not

powered. When the system resumes from S3, the system context remains intact because the

system memory was preserved and powered at all times.

S4 is the Hibernate (Microsoft terminology) or Suspend-to-Disk state. The system context (memory)

is saved to the hard drive as a hibernation file. When the system resumes from S4, the system

context is restored from the hibernation file. V

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remains powered, but all other subsystems

including system memory and the processor are not powered.

S5 is the Soft Off state. It is identical to S4 with the exception that the system context is not

saved. When the system resumes from S5, it will power up and going through POST. S5 is

also known as G2.

G3 is the Mechanical Off state. All subsystems are not powered in this state. The easiest way to

achieve this state is by removing A/C power from the system via unplugging the power cord.

The ME has its own power states (Mx) similar to the Sx states.

M0 is the ON state for the ME when the system is in S0 state. ME is fully powered and running.

M3 is the ON state for the ME when the system is in a non-S0 state. ME is fully powered and

running.

Moff is the OFF state for the ME. The system is in a non-S0 state.

The ME can be set to stay powered and active in all Sx states. If the system (host) is in S0, then the

ME will be in the corresponding M0 state. However, if the system is in S3, S4, or S5, then the ME will

remain active, but it will be in M3 state.