system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If rebooting is turning a system off and then back on again automatically, how does the system turn itself on while being off?
gpt
Whether or not your computer is "on" ( power states of the computer) are controlled by something called the ACPI (Advanced Configuration and Power Interface). When you tell your computer to "shut down", the operating system tells the ACPI to stop all processes. However, your computer does not actually completely power down, it has some stored juice with which it can restart itself when asked. This is called a standby power supply. The power button these days does not actually physically stop electricity to flow into the computer, it just tells a subroutine to go into a standby and wait for a new input to restart itself. At the end of a shutdown process, your computer tells the ACPI that the computer should reboot. When this happens, the components are reset with commands stored in them by the bootstrapping process (booting, as it were). So in other words, as long as the power is connected these days, the computer never actually turns off, it only resets various components and then behaves as if it was turned off.