4.2.3. GRUB features
This boot method is called direct loading because
instructions are used to directly load the operating system, with
no intermediary code between the boot-loaders and the operating
system's main files (such as the kernel). The boot process used by
other operating systems may differ slightly from the above,
however. For example, Microsoft's DOS and Windows operating systems
completely overwrite anything on the MBR when they are installed
without incorporating any of the current MBR's configuration. This
destroys any other information stored in the MBR by other operating
systems, such as Linux. The Microsoft operating systems, as well as
various other proprietary operating systems, are loaded using a
chain loading boot method. With this method, the MBR points to the
first sector of the partition holding the operating system, where
it finds the special files necessary to actually boot that
operating system.
GRUB supports both boot methods, allowing you to use it with
almost any operating system, most popular file systems, and almost
any hard disk your BIOS can recognize.
GRUB contains a number of other features; the most important
include:
-
GRUB provides a true command-based, pre-OS environment on x86
machines to allow maximum flexibility in loading operating systems
with certain options or gathering information about the system.
-
GRUB supports Logical Block Addressing (LBA) mode, needed to
access many IDE and all SCSI hard disks. Before LBA, hard drives
could encounter a 1024-cylinder limit, where the BIOS could not
find a file after that point.
-
GRUB's configuration file is read from the disk every time the
system boots, preventing you from having to write over the MBR
every time you change the boot options.
A full description of GRUB may be found by issuing the info grub command
or at
the GRUB site. The Linux Documentation Project has a
Multiboot with GRUB Mini-HOWTO.
