Boot

To boot a computer is to turn it on. Booting can refer to either a hard boot from a powered-off state or a soft boot (or "reboot") that restarts it when it's already on. Computers have a boot sequence that takes place after they power on before they are usable.

The first step in the boot sequence happens when you press the computer's power button. The power supply delivers electricity to the motherboard, which initiates the boot process. The computer starts the POST (Power On Self Test), which verifies the integrity of the CPU, memory, and other components. Next, the computer loads startup instructions from its ROM — either the BIOS (in older computers) or the UEFI (in modern computers). It checks its storage devices and loads the operating system from the boot disk. Once the operating system loads, the computer is ready to use.

In most cases, there's nothing that you need to do during the boot process. However, you are allowed to intervene at certain times. After the POST, the computer displays a list of keys you can press to change BIOS settings and the boot disk order, although the exact keys used may vary.