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.
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.
Figure 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 80 01 .........N...... 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.
Viruses Can Infect the Master Boot Record
Many destructive viruses damage the Master Boot Record and make it impossible to start the computer from the hard disk. Because the code in the Master Boot Record executes before any operating system is started, no operating system can detect or recover from corruption of the Master Boot Record. You can use, for example, the DiskProbe program on Windows NT Workstation Resource Kit CD to display the Master Boot Record, and compare it to the Master Boot Record shown above. There are also utilities on the Microsoft Windows Resource Kits that enable you to save and restore the Master Boot Record.
For more detailed information see resource kits on Microsoft's web site or Microsoft Developers Network (MSDN) http://msdn.microsoft.com
