It is the first thing when the system starts. It has majorly 5 phases
* Hardware : BIOS fired up and checks for the hardware connection
* Operating System Loader : The OS loader is located in the initial 512-byte block of the boot device known as the MBR
* Kernel : It initializes various components of the computer, operating system and each portion of software responsible for task, usually consider a driver
* root user-space process (init and inittab) : This defines what should be run when the /sbin/init program is instructed to enter a particular run-level, giving the administrator an easy way to establish an environment for some usage
* Boot scripts : For each managed service (mail, nfs server, cron, etc.), there is a single startup script located in a specific directory.
