Operating System Booting

Booting is the process of loading the operating system into memory and, thereby, launching the OS. It occurs in several stages:

1. When the power button is pressed, a hardware interrupt that takes place causes the copying of an address to one of the CPUs. This address points to the 1st instruction of the bootstrap program (or boot loader) program on the read-only memory (ROM) section of memory.
2. Since the data of the boot loader software is already inside main memory, the boot loader starts running.
3. While running, the program checks that all the essential hardware devices are connected and available for use.
4. If all the necessary hardware devices pass the check, the program continues to find the storage location of the OS kernel program on disk.
5. The bootstrap program copies the instructions of the OS Kernel into memory, and the OS begins running.
6. The OS mounts the root file system. That is, the OS finds the location on the disk of the root directory and establishes access to it.