"GRUB has been with us for a while, replacing LILO (Linux
Loader) before it, and adequately performs its task of allowing you
to boot multiple operating systems (including Windows) and even
multiple kernels within operating systems (at least with respect to
Linux) without too much hassle.
"But it had its limitations. It wasn't particularly pretty, it
was hard to make custom menus, and most importantly didn't natively
recognise drive UUIDs (universally unique identifier), so it was
dependent on the system's BIOS to correctly identify drives. The
latter is a useful feature: as every drive has its own UUID, and
you can add or remove drives from a system, or even take them to
another computer, and you will always be able to boot the correct
drive regardless of how the BIOS identifies them."