Wikipedia
In computing, booting is the process of starting a computer It can be initiated by hardware such as a button press, or by a software command After it is switched on, a computer's central processing unit (CPU) has no software in its main memory, so some process must load software into memory before it can be executed This may be done by hardware or firmware in the CPU, or by a separate processor in the computer system Restarting a computer also is called rebooting, which can be "hard", eg after electrical power to the CPU is switched from off to on, or "soft", where the power is not cut
Booting#Modern_boot_loaders - Wikipedia, the free encyclopedia