Booting is a process of loading Operating System(OS) to primary storage(usually Random Access Memory[RAM]), and readying a computer system for use. This process is carried out using a firmware which loads a small program from a special region in in hard disc,floppy disk, optical disc or other storage devices. This region is known as Boot Sector.
Boot sector is a first sector on a disk which contains boot record(a machine code) which is loaded into RAM by ROM(BIOS) firmware which in turn loads OS/start-up program into RAM to make the computer into a meaningful machine. There are mainly two types of boot sector:
- Master Boot Record(MBR): For partitioned storage device MBR is the first sector. Hard disk drives
- Volume Boot Record(VBR): For non-partitioned storage device VBR is the first sector. Floppy disk, USB flash drive.
BIOS does not know about MBR or VBR it simply looks for the first sector of the storage device. VBR which holds the code for booting invoked either directly by the BIOS or indirectly by MBR. In non-partitioned device there is only VBR which is the first sector. In partitioned device VBR is the first sector of an individual partition. The MBR, which understand the disk partitioning of the storage device, invokes the VBR of a partition (primary/active partition) which set to boot, loads OS or other start up program installed within that partition
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