21.1. Introduction to Boot Loaders

When a Linux system running on PC hardware is started, the first code to be run is the BIOS (Basic Input Output System) which is loaded from ROM. After it has finished testing the system's memory and discovering what hardware is installed, it attempts to pass control to an operating system boot loader to continue the boot process. The boot loader is a tiny program that may prompt the user to choose which OS to run, and then loads the rest of the operating system kernel from a hard drive, floppy disk, or some other source.

On a normal system, the boot loader is loaded by the BIOS from the first block on the primary hard drive, called the master boot record or MBR. The BIOS, however, may (depending on its configuration) ...

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