In computing, booting (or booting up) is the initialization of a computing system. The booting process can be “hard”, e.g., after electrical power to the processor is switched from off to on (in order to diagnose particular hardware errors or reset the computing system), or “soft”, when power on self-tests (POST) can be avoided. Both hard and soft booting can be initiated by hardware activation such as a button press, or by software command. Booting is complete when the normal, operative, runtime environment is attained.
On some computers, the boot up process can take tens of seconds, or even minutes, and typically involves performing a power-on self-test, locating and initializing peripheral devices, and then finding, loading and starting the operating system (OS). For some servers with a large number of I/O channels, dual in-line memory modules (DIMMs), and peripherals, performing testing of system components prior loading the OS may result in long boot times.