Answer : 3. "BIOS"
Explanation :

The instructions about booting your system are stored in the Basic Input/Output System (BIOS) or its modern equivalent, Unified Extensible Firmware Interface (UEFI). BIOS/UEFI is firmware that is built into the computer's motherboard and contains low-level software that initializes and initializes hardware components, including the system boot process. It provides the necessary instructions for the computer to boot up and load the operating system from the storage device.