Master Boot Record (MBR)

The Master Boot Record, created when you create the first partition on the hard disk, is probably the most important data structure on the disk. It is the first sector on every disk. The location is always track (cylinder) 0, side (head) 0, and sector 1.

The Master Boot Record contains the Partition Table for the disk and a small amount of executable code. On x86-based computers, the executable code examines the Partition Table, and identifies the system partition.

The Master Boot Record then finds the system partition's starting location on the disk, and loads an copy of its Partition Boot Sector into memory. The Master Boot Record then transfers execution to executable code in the Partition Boot Sector.

ntfs note

Note:
Although there is a Master Boot Record on every hard disk, the executable code in the sector is used only if the disk is connected to an x86-based computer and the disk contains the system partition.

The example below shows a hex dump of the sector containing the Master Boot Record. The figure shows the sector in two parts:

  • The first part is the Master Boot Record, which occupies the first 446 bytes of the sector. The disk signature (FD 4E F2 14) is at the end of the Master Boot Record code.
  • The second part is the Partition Table.
Physical Sector:Cyl 0,Side 0,Sector 1  
  
  00000000:00 33 C0 8E D0 BC 00 7C -8B F4 50 07 50 1F FB FC .3.....|..P.P..  
  00000010:BF 00 06 B9 00 01 F2 A5 -EA 1D 06 00 00 BE BE 07 ................  
  00000020:B3 04 80 3C 80 74 0E 80 -3C 00 75 1C 83 C6 10 FE ...<.t..<.u.....  
  00000030:CB 75 EF CD 18 8B 14 8B -4C 02 8B EE 83 C6 10 FE .u......L.......  
  00000040:CB 74 1A 80 3C 00 74 F4 -BE 8B 06 AC 3C 00 74 0B .t..<.t.....<.t.  
  00000050:56 BB 07 00 B4 0E CD 10 -5E EB F0 EB FE BF 05 00 V.......^.......  
  00000060:BB 00 7C B8 01 02 57 CD -13 5F 73 0C 33 C0 CD 13 ..|...W.._s.3...  
  00000070:4F 75 ED BE A3 06 EB D3 -BE C2 06 BF FE 7D 81 3D Ou...........}.=  
  00000080:55 AA 75 C7 8B F5 EA 00 -7C 00 00 49 6E 76 61 6C U.u.....|..Inval  
  00000090:69 64 20 70 61 72 74 69 -74 69 6F 6E 20 74 61 62 id partition tab  
  000000A0:6C 65 00 45 72 72 6F 72 -20 6C 6F 61 64 69 6E 67 le.Error loading  
  000000B0:20 6F 70 65 72 61 74 69 -6E 67 20 73 79 73 74 65 operating syste  
  000000C0:6D 00 4D 69 73 73 69 6E -67 20 6F 70 65 72 61 74 m.Missing operat  
  000000D0:69 6E 67 20 73 79 73 74 -65 6D 00 00 80 45 14 15 ing system...E..  
  000000E0:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  000000F0:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000100:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000110:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000120:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000130:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000140:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000150:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000160:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000170:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000180:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  00000190:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  000001A0:00 00 00 00 00 00 00 00 -00 00 00 00 00 00 00 00 ................  
  000001B0:00 00 00 00 00 00 00 00 -FD 4E F2 14 00 00       .........N......  
                                                      80 01               ..  
  000001C0:01 00 06 0F 7F 96 3F 00 -00 00 51 42 06 00 00 00 .....?...QB....  
  000001D0:41 97 07 0F FF 2C 90 42 -06 00 A0 3E 06 00 00 00 A....,.B...>....  
  000001E0:C1 2D 05 0F FF 92 30 81 -0C 00 A0 91 01 00 00 00 .-....0......... 
  000001F0:C1 93 01 0F FF A6 D0 12 -0E 00 C0 4E 00 00 55 AA ...........N..U.
 

For more detailed information see resource kits on Microsoft's web site
or Microsoft Developers Network (MSDN)

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