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Comment by koolba | Hacker News Reader

That’s pretty funny though I don’t think it’d work on a modern setup as everyone I’ve seen for the past 20 or so years does a hard power off after holding down the power button for 5+ seconds.

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This was before the introduction of ACPI, which is what makes that possible. Prior to that, switches in PCs operated more like a latching switch than a momentary switch (regardless of whether it was actually a momentary switch or not), so it was the action of releasing the button that would either send the signal to shutdown, or physically break the circuit supplying power to the computer.

This is where the old "It is now safe to shut down your computer." screens of Windows 9x/NT 3 came from. http://i0.kym-cdn.com/photos/images/original/001/286/950/e05...

Are services still running when that screen is being displayed? I'd have thought that by the time it shows up, all processes are terminated.

It's in the article. The guy pressed the power button on the wrong machine, other than the one that was shut down.

Holding for 5 secs is an ACPI function, ACPI was first released in 1996, so having systems without it around in 1999 wouldn't be surprising.

I've learned coding on such machines, they're quite fun. Easily recognized by the computer requiring a manual powerdown after the OS has shutdown (Win95 showed a message ala "You can powerdown the machine now")

Before ATX and ACPI standards a typical power button was just a switch in power supply's AC circuit:

https://www.youtube.com/watch?v=SYdnPTX0FD8

A model of PS/2 I worked on when I was a teenager had mains voltage across two exposed terminals behind the big power switch. I discovered this when dropping a screwdriver across them.

Had a power supply open to replace the fan, turned it on while open to test if it was wired up correctly. I flicked the switch with my thumb, with two fingers inside the case to stabilise it as the fan was loose. Those fingers briefly touched across the back of the switch and I got 240v mains straight to my hand. Luckily it caused my whole arm to contract so my hand couldn't seize up around the terminals!

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