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ACPI Power states, when do CPU fan, PSU fans turn off/on?

By rodion15
Aug 9, 2015
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  1. In which of the ACPI power states on a desktop computer are the CPU/PSU fans on?

    I guess in S0 all fans are ON. In what of the other states are fans off?
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    Wikipedia: Advanced Configuration and Power Interface:

    • G0 (S0): Working. "Awaymode" is a subset of S0, where monitor is off but background tasks are running.
    • G1, Sleeping subdivides into the four states S1 through S4:
    o S1: All processor caches are flushed, and the CPU(s) stops executing instructions. Power to the CPU(s) and RAM is maintained; devices that do not indicate they must remain on may be powered down.
    o S2: CPU powered off. Dirty cache is flushed to RAM.
    o S3: Commonly referred to as Standby, Sleep, or Suspend to RAM (STR). RAM remains powered
    o 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 is almost the same as G3 Mechanical Off, except that the PSU still supplies power, at a minimum, to the power button to allow return to S0. A full reboot is required. No previous content is retained. Other components may remain powered so the computer can "wake" on input from the keyboard, clock, modem, LAN, or USB device.
    • G3, Mechanical Off: The computer's power has been totally removed via a mechanical switch (as on the rear of a PSU). The power cord can be removed and the system is safe for disassembly (typically, only the real-time clock continues to run - using its own small battery).
     

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