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MBR - Master Boot Record:

Microsoft: "On startup, at the end of the ROM BIOS bootstrap routine, the BIOS reads and executes the first physical Sector of the first Floppy (A:\) or Hard Disk (C:\) on the system. This first sector of the hard disk is called the Master Boot Record (or sometimes the partition table or master boot block)."

There is a small program at the beginning of this sector of the hard disk. The Partition information, or Partition Table, is stored at the end of this Sector. This program uses the partition information to determine which partition is bootable (usually the first primary DOS partition) and attempts to boot from it.

In other words, the MBR contains pointers to the first sector of the Partition containing the Operating System, and that Sector contains the instructions that cause the computer to Boot the Operating System.

This program is written to the disk by the fdisk /mbr command and is usually referred to as the Master Boot Record. During typical operation, Fdisk writes this program to the disk only if there is no Master Boot Record.

PowerQuest: "The master boot record is contained in the first sector of the first physical hard disk. The MBR consists of a master boot program and a partition table that describes the disk partitions. The master boot program looks at the Partition Table to see which Primary Partition is Active. It then starts the Boot program from the Boot Sector of the Active Partition.

The smallest addressable piece of space on the hard drive is the sector. The MBR is contained in the Sector located at cylinder 0, head 0, sector 1 of the hard disk, and is created by a Disk Utility such as the DOS FDISK utility. Each Operating System has a program similar to FDISK that creates a functionally similar MBR.

Each sector of a hard drive contains 512 bytes; the MBR is no exception. The first 446-bytes of the MBR contains a program that is executed each time the Hard Disk is Booted; the rest of the record contains a 2-byte header, and, most importantly, four 16-byte partition table entries.

Each Partition Table entry within the Master Boot Record contains valuable information about your Partitions"

GB: If a Virus destroys the MBR, it must either be restored, repaired or rewritten. Your Data may remain intact on the Disk but unavailable if you're lucky!

  1. Master File Table - MFT for NTFS File System.
  2. images/bullet2.gifwww.microsoft.com/technet - Repairing Damaged MBRs and Boot Sectors in x86-based Computers:
  3. images/bullet2.gifwww.microsoft.com/technet - Restoring the MBR:
  4. images/bullet2.gifNTFS.com Fixing and repair MBR - Master Boot Record:
  5. grc.com:  CIH Virus Recovery -
  6. 69013 - FDISK -MBR Rewrites the Master Boot Record
  7. Phoenix Technologies - See: Phoenix White Papers and Specs, BIOS Boot Specification.
  8. Hale's HIW Master Boot Record: Disassembly of a Master Boot Record (MBR)
  9. PowerQuest.com:  How the Master Boot Record Works
  10. 171611 - Removing the Linux LILO Boot Manager: From Win2000.
  11. 266745 - Error Message When You Run fixmbr Command: Win2000 Error Message By Design!
  12. 222188 - Upgrading the System or Boot Drive to Dynamic (Rooting): Win2000
  13. 320283 - You Cannot Revert a Disk to a Basic Disk If the Disk Appears As Dynamic Unreadable in Disk Management: Win200 & WinXP Pro.
  14. 282793 - HOW TO Change a GUID Partition Table Disk into a Master Boot Record Disk in Windows XP
  15. 80304 - Missing Operating System and No ROM BASIC Error Messages: From DOS 6.
  16. 149877 - Boot Record Signature AA55 Not Found:
  17. www.FDisk.com:
  18. www.MBR-Recovery.com:
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Web Development, Gill Boyd & Team - Posted 12/07/2002; Updated 11/09/2003