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Thread: What's the difference between PWM and "auto" fan control in BIOS?

  1. #1
    Join Date
    Nov 2012

    Default What's the difference between PWM and "auto" fan control in BIOS?

    Not sure if this is a standard distinction, I can't control the CPU fan (which has 4 pins and the system can control it under load) with Speedfan with either setting. FWIW I have the GA-M55SLI-S4 1.0 with the Beta F11j BIOS.

  2. #2
    Join Date
    Dec 2010
    Near Toronto but not in it

    Default Re: What's the difference between PWM and "auto" fan control in BIOS?

    PWM is the most sure way of confirming fan speed rotation. if that fan is commanded at 1500rpm and the MB senses that the fan is spinning at 1450rpm it will compensate the difference, increase the voltage and make it 1500RPM. possibly with your MB being set to Auto is disabling the control from windows?

    in your MB, Auto sets the follwing; BIOS autodetects the type of CPU fan you installed and sets the optimal CPU Smart FAN control mode for it. (Default Value)

    But for this to operate properly you also have to enable CPU Smart FAN Control, and your CPU has to support it.

    I would try to disable CPU Smart Fan and then set the fan control to PWM and then see it you can control it in windows. only issue with that is if overclocking, you may not be adaquately cooling the system during bootup.

    but it could be worth a try.

    Main Rig
    OS = Win10-64Bit
    CPU = Ryzen 1700x Overclocked to 4Ghz with custom water-cooling loop
    Mem = 16GB RAM @ 3200Mhz
    MB = Asus ROG C6H
    GPU = Asus 1080Ti ROG Strix
    HD = 512GB M.2 Samsung 960 Pro
    PSU = EVGA SuperNOVA 1300w
    Case = Cooler Master HAF-X 945

    HTPC / Home Server
    OS = Win7 64Bit running XBMC HTPC Front end with Windows Server 2012 Virtual Machine with 12GB ram assigned for homer server
    CPU = i7-980X @ 3.5Ghz CoolerMasster Hyper 212 Evo
    Mem = 24GB RAM
    MB = Gigabyte GA-X58A-UD5 v1.0 with F6 Bios
    GPU = EVGA nVidia GT210
    HD = 2x PNY 120GB Raid 0 (OS)
    Storage = 8TB WD Black Storage
    PSU = Corsair TX750
    Case = Define R5

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