(Master Boot Record)
All disks start with a boot sector. When you start the computer, the code in the MBR executes before the operating system is started. The location of the MBR is always track (cylinder) 0, side (head) 0, and sector 1. The MBR contains a file system identifier. Master Boot Record is probably the most important data structure on the disk. The MBR contains the Partition Table for the disk and a small amount of executable code.