- The first instructor of the bootstrap loader program of an operating system is stored in BIOS(Basic Input/Output System). - The bootstrap loader is a programme that resides on the EPROM, ROM or other non-volatile memory of the machine. - It is executed by the processor automatically when the device is turned on. To continue installing the computer's operating system, the bootstrap loader reads the boot sector of the hard drives. - The bootstrap loader first conducts the power-on self-test, also referred to as POST, when the machine is switched on or restarted. - The bootstrap loader loads the operating system for the machine into memory if the POST is successful and no problems are found. - It is then possible for the machine to access, load, and operate the operating system. - In computers that have an EFI (Extensible Firmware Interface), the bootstrap loader has been replaced and is now part of the EFI BIOS.