Master Boot Record

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Revision as of 14:49, 21 November 2009 by Misfit138 (talk | contribs) (grammar)
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Most PCs today use firmware called the BIOS (Basic Input/Output System). The BIOS is typically contained within a CMOS (Ceramic Metal Oxide Semiconductor) and executes upon system power-up, when it then initializes system devices. After system devices have been initialized, the BIOS then launches a program on the Master Boot Record (MBR). The MBR is the first sector (first 512 bytes) of a storage device (hard disk drive, solid state drive, CD/DVD drive, USB drive...). The BIOS launches the program on the MBR of the first recognized BIOS boot device on your computer. This program (also known as a bootloader) reads the partition table (also contained within the MBR) and eventually boots the operating system(s). Common GNU/Linux bootloaders include GRUB and LILO.

Backup and Restoration

Warning: Restoring the MBR with a mismatching partition table will make your data unreadable and nearly impossible to recover. If you simply need to reinstall the bootloader see GRUB or LILO.

Because the MBR is located on the disk it can be backed up and later recovered.

To backup the MBR:

dd if=/dev/hda of=/path/mbr-backup bs=512 count=1

Restore the MBR:

dd if=/path/mbr-backup of=/dev/hda bs=512 count=1

To erase the MBR (may be useful if you have to do a full reinstall of another operating system):

dd if=/dev/zero of=/dev/hda bs=446 count=1