Boot Loader program which invokes booting of the system is stored in

Concept

Any program the CPU must run the instant power is applied has to live in non-volatile memory that is already populated before any disk or operating system is available. Read-Only Memory (ROM) is firmware memory whose contents are fixed at manufacture and survive power loss, so the processor can fetch its very first instructions from a known fixed address inside ROM.

Application

When a machine is switched on, RAM is empty and the disk has not yet been read. The CPU therefore jumps to a hard-wired reset address that maps into ROM, where the bootstrap/boot-loader firmware (the BIOS/UEFI bootstrap code) resides. That firmware initialises the CPU and memory, then locates a bootable device and pulls the next stage into RAM. Because this code must exist before anything else runs, it is permanently stored in ROM.

Why the other choices fail

• RAM is volatile: it holds nothing at power-on, so it cannot be the place the first boot code is stored.

• The hard disk's track 0 holds the Master Boot Record, but that sector is only read by code that is already executing from firmware; the program that invokes booting must run before the disk is touched.

• "Any device" is too loose: the initial bootstrap is fetched from one fixed, non-volatile firmware location, not from an arbitrary device.

Result

The boot-loader firmware that invokes booting is stored in ROM.