Comment by numpad0

ACPI defines power state of power-saving capable offbrand fake IBM computers(among other things, and also the "fake IBM" part is almost completely moot at this point).

ACPI power state S0 is everything running. S1 pauses CPU and CPU I/O bus. S2 puts CPU to reset. S3 cuts power to CPU. S4 cuts off everything(not actual power off). S5 cuts off everything(actual power off).

S3 and S4 are often referred to as Sleep and Hibernation. In Sleep, RAM contents are kept as-is, and sleep handling code just restore CPU internal states that gets lost. In Hibernation, OS usually dump RAM contents to disk, and write back to RAM upon bootup - S4 and S5 aren't always clearly separated and both Windows and Linux tend to go through standard boot processes, then do the state resume using RAM dump they find on disk.

For SOME reason, Microsoft forced laptop vendors to quit supporting S3 in favor of their custom "S0iX" state, which is more or less just machine running at full power, which can be extremely wasteful as far as sleep state goes.

The official explanation for this pressuring is that everybody want notification and this is the only way Windows could possibly handle notifications. A lot are skeptical about that.

1: https://learn.microsoft.com/en-us/windows-hardware/drivers/k...