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(grub.info)Overview

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Overview
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   Briefly, a "boot loader" is the first software program that runs when
a computer starts.  It is responsible for loading and transferring
control to an operating system "kernel" software (such as the Linux or
GNU Hurd kernel).  The kernel, in turn, initializes the rest of the
operating system (e.g. a GNU system).

   GNU GRUB is a very powerful boot loader, which can load a wide
variety of free operating systems, as well as proprietary operating
systems with chain-loading(1) (Note: Overview-Footnote-1). GRUB is
designed to address the complexity of booting a personal computer; both
the program and this manual are tightly bound to that computer platform,
although porting to other platforms may be addressed in the future.

   One of the important features in GRUB is flexibility; GRUB
understands filesystems and kernel executable formats, so you can load
an arbitrary operating system the way you like, without recording the
physical position of your kernel on the disk.

   Thus you can load the kernel just by specifying its file name and the
drive (and the partition) where the kernel resides. To let GRUB know the
drive and the file name, you can either type in them manually via the
command-line interface (Note: Command-line interface), or use the nice
menu interface (Note: Menu interface) through which you can easily
select which OS it boots. To allow you to customize the menu, GRUB will
load a preexisting configuration file (Note: Configuration). Note that
you can not only enter the command-line interface whenever you like, but
also you can edit specific menu entries prior to using them.

   In the following chapters, you will learn how to specify a drive or a
partition, and a file name (Note: Naming convention) to GRUB, how to
install GRUB on your drive (Note: Installation), and how to boot your
OSes (Note: Booting), step by step.