Boot process (or booting) is the initial phase of powering on the computer and preparing it to work with applications. The process includes all the operations that take place at boot time, like testing the hardware, configuring devices, and loading the operating system into the computer’s RAM.
Booting is started by the bootloader, a program that resides on the computer’s firmware or boot partition. When the computer is turned on, the bootloader is transferred to RAM, from where it coordinates loading of the OS kernel.