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What is MBR - The Master Boot Record?

The Master Boot Record, the first sector on the disk. Contains the partition tables (a list that describes the locations of partitions on the disk).

Short for Master Boot Record, a small program that is executed when a computer boots up. Typically, the MBR resides on the first sector of the hard disk. The program begins the boot process by looking up the partition table to determine which partition to use for booting. It then transfers program control to the boot sector of that partition, which continues the boot process. In DOS and Windows systems, you can create the MBR with the FDISK /MBR command.
An MBR virus is a common type of virus that replaces the MBR with its own code. Since the MBR executes every time a computer is started, this type of virus is extremely dangerous. MBR viruses normally enter a system through a floppy disk that is installed in the floppy drive when the computer is started up. Even if the floppy disk is not bootable, it can infect the MBR.

The Task of the MBR

The normal job of the MBR program is to search the partition table for the active partition, copy the boot sector from the active partition into memory, and transfer control over to that program. If the MBR cannot accomplish this task successfully, it will print one of these error messages:

  • Invalid partition table
  • Error loading operating system
  • Missing operating system

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