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PC Power Management Guide Rev. 2.0
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ACPI Power Management States

These are the power management states as defined in the ACPI specification. I’ll go through them briefly but let's get a big picture of it first. The details of each and every state will be described in the following sections.

Global system states

  • The entire system state which is visible to user.
  • Divided into 4 states – G0, G1, G2, G3

Sleeping states

  • They are the sleeping states resides in global system state G1 (except S5)
  • Divided into 5 states – S1, S2, S3, S4, S5

Device Power states

  • This power state is usually invisible to user.
  • When a device is at ‘on’ state, another one might be in ‘off’ state.
  • Divided into 4 states – D0, D1, D2, and D3.

CPU Power states

  • Also known as CPU sleep states.
  • It is within the global system state G0
  • So far divided into 5 states – C0, C1, C2, C3, and C4.
  • In future, there will be up to C6 states (Penryn).

CPU / Device Performance states

  • CPU / Device power management when it is still active.
  • Usually clock speed and voltage varies depend on workload.
  • The amount of P-state is CPU / Device specific
  • Eg. Higher clock ratio CPU will have more P-states than a lower clock ratio CPU

CPU Thermal Monitor

  • It throttles the CPU to a lower performance state when temperature exceeds the threshold.
  • In TM1, throttling is done via changing its duty cycle.
  • In TM2, throttling is done via changing its clock speed and core voltage (P-state).

<<< Introduction : Previous Page   |   Next Page : Global System States (G-States), Global States Summary >>>


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