grub2 - The GRand Unified Bootloader.

GNU GRUB is a very powerful boot loader, which can load a wide variety of
free operating systems, as well as proprietary operating systems. GRUB is
designed to address the complexity of booting a personal computer.

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 partition where
the kernel resides.