Bootloader

From Linux 101, The beginner's guide to all things Linux.

The bootloader is what loads your operating system. The bootloader is normally kept in the Master Boot Record (MBR) of the primary disk. It may prompt the user to select an operating system to boot, or automatically start the operating system.

With many operating systems, the booting process simply involves having the bootloader on the MBR pass control to the boot area of the partition containing the operating system to be booted. With Linux, the bootloader actually accesses the filesystem containing the kernel and passes control to it directly. This distinction allows multiple kernels to be kept on the same filesystem, which makes switching to a new kernel easier.

Two commonly used bootloaders for Linux (and any coexisting operating systems) are LILO and GRUB.