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Master Boot Record (MBR)

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Definition: A master boot record is a kind of boot sector stored on a hard disk drive or other storage device.

The master boot record on a hard drive contains the necessary computer code to start the boot process.

A master boot record consists of three major pieces: the master partition table, the disk signature, and the master boot code.

The master boot record is created when a hard drive is partitioned but is not located within a partition. The master boot record is located on the first sector of a disk. The specific address on the disk is Cylinder: 0, Head: 0, Sector: 1.

In Windows 7 and Windows Vista, you can repair a corrupted master boot record using the bootrec command from System Recovery Options.

In Windows XP, the master boot record can be repaired using the fixmbr command. See How To Repair the Master Boot Record in Windows XP for help.

A volume boot record is another type of boot sector.

Also Known As: MBR, master boot sector, "sector zero"
Examples:
"The new antivirus program I started using scans my PC during the boot process for viruses that attack the master boot record. I once had a virus destroy mine and the computer wouldn't start at all after that!"

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