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Although I don't know this for sure, I'm pretty sure that holding the power button on all computers will force them to shutdown after varying lengths of time. This is particularly useful if the computer freezes, or some other error necessitates a total reboot.
What I'm interested in is whether this force-shutdown mechanism is hardcoded into the computers underlying firmware? Or whether this is built into the computer on a hardware level. If the mechanism was firmware, then it is logical to assume that a CPU-level error would prevent this mechanism from properly triggering, which leads me to believe this is a hardware function.
To summarise: Is the universal (I assume) force-shutdown mechanism built in at a hardware or firmware level? And can someone elaborate on the mechanisms nature, variants and general history.
None. It is done in software. – user207421 – 2017-04-02T10:01:54.197
7@EJP Wrong. See my answer :) – DavidPostill – 2017-04-02T11:11:06.943
2On some of the custom devices I've worked with that also have a soft power button and are battery powered (making a hard power cycle difficult for a user), we explicitly add a separate microcontroller or timer+logic circuits (or a dedicated section on an FPGA) to handle power when the firmware is sufficiently complex to allow for a hard power off if there's a firmware bug that locks it. – Jason C – 2017-04-02T13:42:12.603
4Most statements with "all" are wrong. – Paŭlo Ebermann – 2017-04-02T17:23:42.623
2If all else fails there is a further fully hardware backup solution involving a thick black cord at the back with a 3 pin connector, removing this will also force shutdown. – Darren H – 2017-04-03T07:54:35.430
3@DarrenH not on a laptop with a non-removable battery. Flattenting the battery would work but mine has 10+ hours life (for example) – Chris H – 2017-04-03T08:04:05.647