System Initialization
When ever system boot up in Linux the following three steps happen.
Boot Hardware
On the basic information in the system store in read only memory
Example: BIOS the system examines and startup the hardware.
Some of that information will direct the computer to examine the devices for locating the bootable operating system,
Start Boot loader
Then there control passes to the start boot loader. The boot loader will be started and permits to select to boot Linux or any other operating system
Boot the kernel
Finally there control passes to kernel.
In that time Linux kernel will be loaded.
That kernel mount main file system and passes control to the init process.