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+.. -*- coding: utf-8; -*-
+.. include:: HEADER.rst
+
+==================
+ Power management
+==================
+
+* ACPI power states.
+
+ http://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface
+
+** Global states.
+
+ * G0 (S0) Working
+ * G1 Sleeping (subdivides into the four states S1 through S4)
+
+ * S1: All processor caches are flushed, and the CPU(s) stop executing
+ instructions. Power to the CPU(s) and RAM is maintained; devices that do
+ not indicate they must remain on may be powered down.
+ * S2: CPU powered off.
+ * S3: Commonly referred to as Standby, Sleep, or Suspend to RAM. RAM
+ remains powered.
+ * S4: Hibernation or Suspend to Disk. All content of main memory is saved
+ to non-volatile memory such as a hard drive, and is powered down.
+ * G2 (S5) Soft Off. G2, S5, and Soft Off are synonyms. G2 is almost the same
+ as G3 Mechanical Off, but some components remain powered so the computer
+ can "wake" from input from the keyboard, clock, modem, LAN, or USB device.
+ * G3 Mechanical Off: The computer's power consumption approaches close to
+ zero, to the point that the power cord can be removed and the system is
+ safe for dis-assembly (typically, only the real-time clock is running off
+ its own small battery).
+
+** System states.
+
+ * S0 Working (G0), Processor in C0-C3, full context save RAM maintained
+ * S1 Sleeping with processor context maintained, RAM maintained
+ * S2 Sleeping with processor content not necessarily maintained, RAM
+ maintained, most devices in D3
+ * S3 Sleeping, lower than S2, RAM maintained, most devices in D3
+ * S4 Sleeping, lower than S3, RAM not maintained, most devices in D3
+ * S5 Sleeping, lower than S4, no context saved, reboot necessary
+
+** Device states.
+
+ * D0 Fully-On is the operating state.
+ * D1 and D2 are intermediate power-states whose definition varies by device.
+ * D3 Off has the device powered off and unresponsive to its bus.
+
+** Processor states.
+
+ * C0 is the operating state.
+ * C1 (often known as Halt) is a state where the processor is not executing
+ instructions, but can return to an executing state essentially
+ instantaneously. All ACPI-conformant processors must support this power state.
+ * C2 (often known as Stop-Clock) is a state where the processor maintains all
+ software-visible state, but may take longer to wake up. This processor
+ state is optional.
+ * C3 (often known as Sleep) is a state where the processor does not need to
+ keep its cache coherent, but maintains other state. Some processors have
+ variations on the C3 state (Deep Sleep, Deeper Sleep, etc.) that differ in
+ how long it takes to wake the processor. This processor state is optional.
+
+** Performance states.
+
+ * P0 max power and frequency.
+ * P1 less than P0, voltage/frequency scaled.
+ * Pn less than P(n-1), voltage/frequency scaled.
+
+* Control power schema under Windows.
+
+Use powercfg utility. To se current state:
+
+ cmd> powercfg /QUERY
+
+To see all available states:
+
+ cmd> powercfg /LIST
+
+To restore power configurtion:
+
+ cmd> powercfg /RestoreDefaultPolicies
+
+* Intel.
+
+** Intel Speedstep® Technology.
+
+ http://www.intel.com/support/processors/sb/CS-028855.htm
+ Frequently asked questions for Intel Speedstep® Technology
+ http://www.intel.com/p/en_US/support/highlights/processors/frequencyid
+ Intel® Processor Frequency ID Utility
+ http://software.intel.com/en-us/articles/enhanced-intel-speedstepr-technology-and-demand-based-switching-on-linux
+ Enhanced Intel SpeedStep® Technology and Demand-Based Switching on Linux