The Master Boot Record (MBR) is created when the hard disk is partitioned. The MBR has master boot code, disk signature (or end of sector marker)) and a partition table for the disk. The MBR scans the partition table for the active partition and then finds the starting sector of the active partition. It then loads a copy of the boot sector from the active partition into memory and finally transfers control to the executable code in the boot sector. This means that the MBR identifies the operating system on the disk.
MBR can become corrupted due to human error, hardware problems, power fluctuations, virus attack, and other factors. An Invalid boot disk error is caused when the MBR is either corrupted or when it cannot find the partitions or the boot sector. Sometimes, it might pop an Invalid partition table or Error loading operating system or Missing operating system errors.
