The Master Boot Record (MBR) is the first boot sector on any partitioned hard disk. It contains information about the size of the hard disk, a small amount of program code, and the partition table, which stores information about the primary and extended partitions of a hard disk.
The MBR record it indicates, where the operating system is so that it can be loaded into the main memory and contains the crucial commands for the start of the operating system. Furthermore small auxiliary programs for the start of the non removable disk.
The master boot record is located on hard disks on surface 0, in sector 1, on head 0 on cylinder 0. On non-partitionable storage media such as floppy disks it is the volume boot record( VBR). When the computer is turned on, the Master Boot Record is read into memory and causes the boot sector to be processed from the floppy or hard disk and the operating system to boot. The Master Boot Record can be infected with boot viruses via floppy disks, which can load themselves into memory unnoticed.