Well, I may as well throw my two cents in here. :)
On computers using a standard ATX power supply, pin #9 on the connector
provides power to the motherboard at all times as long as the PSU itself has AC
wall power power coming in.
Modern motherboards use this "Standby" power to run small always-on power
management circuitry (I believe this is integrated directly into the chipset
these days) which monitors all sources of a "power on" signal, be it the power
button on the case, or a LAN controller, or a built-in watchdog timer, or
what-have you. When such a signal is received, this power management circuitry
pulls pin #16 low to power up all the other voltage lines of the PSU, which
fully turns on the computer.
Optionally, some BIOSes allow the user to choose whether or not to instantly
power up when this pin begins outputting voltage (e.g. when wall power is
restored).
So yes, the motherboard does fire up some circuitry as soon as it gets power,
but it doesn't boot per se.
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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Thursday, January 13th, 2022 at 5:12 PM, Bret Johnson bretj...@juno.com
wrote:
> there is absolutely nothing complicated to have a
>
> "on power return, boot computer"
>
> option. it used to be the default.
You all are missing the point. As soon as the motherboard gets power, it starts
booting. That is how it has always worked.
The problem is how to get the appropriate power to the motherboard in the first
place. If you lose power to the motherboard, either because the power supply
lost its external (wall) source or because something in the power supply went
bad, the computer will boot when power is supplied to the motherboard again.
The problem is, the BIOS and the ACPI are on the motherboard and need power in
order to function, and they can't tell the power supply to turn on if the power
supply is not already supplying power to them. It's a circular regress (or a
"Catch 22").
There is no setting to tell the computer start booting when it first gets power
-- it does that automatically and you can't disable that "feature". The problem
is how to get the power to the motherboard in the first place, and you can't do
that with software that doesn't do anything unless it already has power being
supplied to it and the computer has already started booting.
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