Sixth mechanism

The behaviour then became embodied in the ACPI spec (holding the power button for more than 4 seconds is supposed to transition into G2), but on modern laptops this is usually managed by the embedded controller rather than the switch being inlined with the PSU or battery in any way. And, inevitably, various vendors get this wrong. I've got a Vaio that won't turn off if you oops, because every time the EC blinks the LEDs it forgets the power button state and so doesn't think it's been pressed for long enough.