How-to Autostart a PC Automatically When Connecting it to the Mains Power

I’ve decided it would be good if I could just hide the computer under the table, as I never use the DVD writer, and I can access USB ports for removable storage or debug board via a USB hub on my table. The only problem is that I would have to go under the table to press the power button each time I want to power on the computer. Feasible, but not very convenient. Every morning, I connect a power strip to the mains supply for my computer, monitor, and related equipment, so it would be good if the computer could just start when I connect it. I found out there’s an option in the BIOS of my main board to do just that. Most other people seem to use that feature to be able to automatically restart their computer after a power failure so that they can access it remotely. Some smart power strips such as PowerUSB Watchdog also need that feature to automatically restart a computer if it hangs.

BIOS AC Back Function

In the BIOS of my motherboard (Gigabyte GA-970A-D3), I need to go to Power Management Setup, and change AC Back Function with one of three options:

  • Soft-Off – This is the default setting. When the power comes back, it will always stay in power off mode until you press the power button
  • Full-On – Each time the AC power is connected, the computer will automatically start. This is the setting that fulfills my needs.
  • Memory – If you turn off the PC normally, and you disconnect the computer from the mains or there is a power failure when it’s off, the computer will not start automatically. If the computer was running when the power was cut, then it will start automatically.

Selecting Full-On does exactly what I need. Whenever AC power is ON, the computer will auto-run without having to press the power button.

The exact option depends on the BIOS, but I’ve read most recent motherboards should support this feature. This method is OS-independent, so it would work with Linux based distributions, Windows, MAC OS X or any other operating systems you may use.

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11 Replies to “How-to Autostart a PC Automatically When Connecting it to the Mains Power”

  1. Once I had a PSU go bad in the manner that it would go out as soon as a significant load starts to be applied;
    and then it would recover after a short while. In combination with the Full-On setting that you suggest, this caused a poweroff-poweron loop on my server, and by the time I [woke up and] noticed it, the server had about +150 poweroff/on cycles on all HDDs; which is NOT exactly great for their lifespan.

    Also in some cases when utility power goes down for a blackout, on restoring it sometimes flashes on/off briefly (or even with various weird voltages) before going into proper operation.

    So I think this needs to be enabled with some caution.

  2. @rm
    Thanks for sharing your experience. I usually disconnect the power at night, but power is flaky here, and I often have power failures, I’ll see how it goes.

  3. I have set up in bios setting in Power management setup Ac Back Function- Always On. It was working Properly but from some days its not working and the second problem is when power come it does not start normally i have to unplug my power cable of my computer and plug it again then it start otherwise not in my server computer. what may be the reason. Plz help

  4. My office PC’s power button is not working. So this information was useful for me. Thanks for share this.

      1. Hi I can’t find this ac back setting in my BIOS, where should I find this setting for auto start the pc. I also attached my bios screen image for reference.

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