1. Turn on system.
2. Sends electronic signal to attached device and record their response in a file.
3. Select bootable partition.
4. Now grub loaded and other process is going
i. initramfs :- it is sudo file system require to kernel load.it is minimal filesystem which is stored in ROM.
ii. vmlinuz :- it is actual kernel.
iii. System.map :- it contain system call and kernel exported symbols.