After the system is powered on, the BIOS ROM performs the following steps during the first part of the boot sequence:
1. The system firmware in the BIOS ROM executes a power-on self test (POST), runs BIOS extensions in peripheral board ROMs, and invokes software interrupt INT 19h, Bootstrap.
2. The INT 19h handler typically performs the standard PC-compatible boot, which consists of trying to read the first physical sector from the first diskette drive, or, if that fails, from the first hard disk. The processor then jumps to the first byte of the sector image in memory.
3. The first sector on a hard disk on an x86/x64 system contains the master boot block, which contains the master boot (mboot) program and the FDISK table, named for the PC program ...