http://www.yolinux.com/TUTORIALS/LinuxTutorialRecoveryAndBootDisk.html

GRUB: GRand Unified Bootloader

GRUB is an operating system independant boot loader and shell. GRUB uses a device naming system which is different and independant of the one used by Linux. For example (hd0,0), the designation "hd0" refers to the first hard drive. The second designation refers the the partition number. Each begin counting from "0". Some systems like BSD may include more designations. Note that GRUB does not distinguish EIDE from SCSI.

Linux device name GRUB name Linux filesystem
(Examples)
/dev/hda1 (EIDE)
or
/dev/sda1 (SCSI) (hd0,0) /boot
/dev/hda2
or
/dev/sda2 (hd0,1) /
/dev/hdb1
or
/dev/sdb1 (hd1,0) /home
/dev/fd0 (fd0,0) /mnt/floppy

Sample config file: /etc/grub.conf (Linked to actual file: /boot/grub/grub.conf).

default=0
timeout=10
splashimage=(hd1,0)/grub/splash.xpm.gz     - Image to be displayed: /boot/grub/splash.xpm.gz which is on the second hard drive, first partition.
title Red Hat Linux (2.4.9-21)
        root (hd1,0)                       - Root of GRUB reference. Same as /boot. See above table.
        kernel /vmlinuz-2.4.9-21 ro root=/dev/sdb6
        initrd /initrd-2.4.9-21.img        - Referenced from GRUB root reference. Hence file: /boot/initrd-2.4.9-21.img

Note: All GRUB paths are referenced from /boot, as defined by the "root" statement.

Create GRUB boot floppy:

[root prompt]#  fdformat /dev/fd0H1440
[root prompt]#  mke2fs /dev/fd0
[root prompt]#  mount -t ext2 /dev/fd0 /mnt/floppy
[root prompt]#  grub-install --root-directory=/mnt/floppy '(fd0)'
[root prompt]#  cp /boot/grub/grub.conf /mnt/floppy/boot/grub/grub.conf
[root prompt]#  umount /mnt/floppy

The small reduced kernel /boot/vmlinuz-…BOOT and support files in /boot can be loaded on the floppy to create other boot options.