MBR stands for master boot record. It is a section of the storage space on a hard disk drive used to maintain the data that is needed to initiate a boot of the computer. Typically, the MBR resides on the first sector of the hard disk, making it easy for the system to locate, read, and execute the files necessary to launch the application. It contains all the codes needed to access the files, and begin the boot.

The Master Boot Record is also sometimes called the "partition sector" or the "master partition table" because it includes a table that locates each partition that the hard disk has been formatted into. 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.

See: Disk Partition, Partition Table, Partition Boot Sector