system
Given the following post, respond as if you're commenting on Reddit:
human
How can a computer tell itself to turn on again when performing a restart?

To clear things up: You have commanded the computer to restart it has turned off, but how does it then initiate the command for it to turn on again?
gpt
The trick is it doesn't fully power anything off (unless you use the Kill switch on the back of the PS) there is always a constant feed of power coming through it. 

Many mainboards have an LED (on the board itself) that remains lit to let you know that the power is still on if it's plugged in.