The
master boot record (MBR), in
IBM PC architecture, is a 512-
byte sector in the beginning of a
hard disk drive that contains a sequence of commands necessary for operating system
bootstrap. The boot routine code contained within the
ROM BIOS code that the
CPU executes during start-up loads and executes the master boot record. The MBR of a drive usually includes the drive's partition table, using which it can load and run the boot record of the partition that is marked with the "active flag". This design allows the BIOS to load any operating system without knowing exactly where to start inside its partition. Because the MBR is read almost immediately when the computer is started, many
viruses operate by changing the code within the MBR. For
Intel processors the sequence of
assembly language commands in the master boot record operates in
real mode.
see boot sector