A short piece of code responsible for loading the full kernel. On the PC, the boot loader occupies the first sector of the boot disk, although the full loader is commonly split into first and second stages: the first stage remains in the boot sector, which is responsible for loading the second stage from subsequent stages. The boot loader is probably one of the least significant parts of an operating system, and there are plenty of boot loaders available for download (the GNU GRUB being one of them).