A boot loader is a program which loads the Operating system into the main memory. This program is deployed when the computer is powered on or rebooted. It takes place after the basic input/output system(BIOS) perform the power on self test(POST) and transfers the control to master boot record(MBR). The MBR contains the boot loaders. A system may have more than one boot loader installed, because each operating system requires a different boot loader in order to boot an operating system. Now these days, Operating systems comes with boot loader pre-installed, such as Microsoft Windows or Mac comes with boot loaders per-installed. If Linux OS is to be installed, there are various types of boot loader available.
Linux Boot loader:
The most common Linux boot loaders are LILO(LInux LOader) and LOADLIN(LOAD LINux). The GRUB(GRand Unified Bootloader) is a boot loader which is installed by default with every distribution of Red Hat Linux, which is open source.
LILO bootloader is designed for those users who pretend to use Linux as there main or only operating system. The system boots up significantly faster with the LILO boot loader. LOADLIN is a boot loader is preferred by those users whose computer have multiple operating system installed in them and uses Linux OS as a secondary operating system. It is also used as a backup boot loader in case the LILO boot loaders fails.