How does the computer turn itself on when told to 'restart'? [closed]

Question

Possible Duplicate:
How does a computer restart itself?

1. if we want to on our PC we press on switch then computer is start..
2. if we want to shutdown our PC we give commond for switchoff .
3. But there is an interesting state between Shutdown and Statup ."Restart..!".

?. what happened internally and How a PC is going shutdown and without press on button it automatically rebooted itself?

Answer 1

ATX power supplies are under the control of the motherboard, not of the switch. Normally the power supply provides only a small standby current; the power switch on such a machine, actually a momentary NO switch, signals the motherboard that it should put the power supply into full operation. An ACPI command is used to tell the motherboard to put the power supply back in standby, shutting the machine down.

But a "restart" is actually just the CPU being sent to a specific location in BIOS and running the boot routines fresh from the beginning.