A boot sector can be found in the first sector of every logical disk. On a floppy disk, the logical disk takes up all of the physical disk and the boot sector lives in the first physical sector. On a hard disk, a boot sector lives at the start of each partition.

An example boot sector

0000  EB 3E 90 4D 53 57 49 4E-34 2E 30 00 02 20 01 00   .>.MSWIN4.0.. ..

0010  02 40 03 00 00 F8 FF 00-3F 00 40 00 3F 00 00 00   .@......?.@.?...

0020  41 DE 1F 00 80 00 29 37-4B 84 32 46 55 4A 49 54   A.....)7K.2FUJIT

0030  53 55 31 32 32 34 46 41-54 31 36 20 20 20 F1 7D   SU1224FAT16   .}

0040  FA 33 C9 8E D1 BC FC 7B-16 07 BD 78 00 C5 76 00   .3.....{...x..v.

0050  1E 56 16 55 BF 22 05 89-7E 00 89 4E 02 B1 0B FC   .V.U."..~..N....

0060  F3 A4 06 1F BD 00 7C C6-45 FE 0F 8B 46 18 88 45   ......|.E...F..E

0070  F9 FB 38 66 24 7C 04 CD-13 72 3C 8A 46 10 98 F7   ..8f$|...r<.F...

0080  66 16 03 46 1C 13 56 1E-03 46 0E 13 D1 50 52 89   f..F..V..F...PR.

0090  46 FC 89 56 FE B8 20 00-8B 76 11 F7 E6 8B 5E 0B   F..V.. ..v....^.

00A0  03 C3 48 F7 F3 01 46 FC-11 4E FE 5A 58 BB 00 07   ..H...F..N.ZX...

00B0  8B FB B1 01 E8 94 00 72-47 38 2D 74 19 B1 0B 56   .......rG8-t...V

00C0  8B 76 3E F3 A6 5E 74 4A-4E 74 0B 03 F9 83 C7 15   .v>..^tJNt......

00D0  3B FB 72 E5 EB D7 2B C9-B8 D8 7D 87 46 3E 3C D8   ;.r...+...}.F><.

00E0  75 99 BE 80 7D AC 98 03-F0 AC 84 C0 74 17 3C FF   u...}.......t.<.

00F0  74 09 B4 0E BB 07 00 CD-10 EB EE BE 83 7D EB E5   t............}..

0100  BE 81 7D EB E0 33 C0 CD-16 5E 1F 8F 04 8F 44 02   ..}..3...^....D.

0110  CD 19 BE 82 7D 8B 7D 0F-83 FF 02 72 C8 8B C7 48   ....}.}....r...H

0120  48 8A 4E 0D F7 E1 03 46-FC 13 56 FE BB 00 07 53   H.N....F..V....S

0130  B1 04 E8 16 00 5B 72 C8-81 3F 4D 5A 75 A7 81 BF   .....[r..?MZu...

0140  00 02 42 4A 75 9F EA 00-02 70 00 50 52 51 91 92   ..BJu....p.PRQ..

0150  33 D2 F7 76 18 91 F7 76-18 42 87 CA F7 76 1A 8A   3..v...v.B...v..

0160  F2 8A 56 24 8A E8 D0 CC-D0 CC 0A CC B8 01 02 CD   ..V$............

0170  13 59 5A 58 72 09 40 75-01 42 03 5E 0B E2 CC C3   .YZXr.@u.B.^....

0180  03 18 01 27 0D 0A 49 6E-76 61 6C 69 64 20 73 79   ...'..Invalid sy

0190  73 74 65 6D 20 64 69 73-6B FF 0D 0A 44 69 73 6B   stem disk...Disk

01A0  20 49 2F 4F 20 65 72 72-6F 72 FF 0D 0A 52 65 70    I/O error...Rep

01B0  6C 61 63 65 20 74 68 65-20 64 69 73 6B 2C 20 61   lace the disk, a

01C0  6E 64 20 74 68 65 6E 20-70 72 65 73 73 20 61 6E   nd then press an

01D0  79 20 6B 65 79 0D 0A 00-49 4F 20 20 20 20 20 20   y key...IO      

01E0  53 59 53 4D 53 44 4F 53-20 20 20 53 59 53 80 01   SYSMSDOS   SYS..

01F0  00 57 49 4E 42 4F 4F 54-20 53 59 53 00 00 55 AA   .WINBOOT SYS..U.

	

Structure of the boot sector

Structure of a FAT disk

disk address	length	contents
0	1	MBR
1	PhysSectPerTrck - 1	Undefined
PhysSectPerTrck	1	Boot sector
PhysSectPerTrck+1	NumFATs*NumSectPerFAT	FATs
BookKeep-SectRootDir	SectRootDir	Root directory
BookKeep	LogcDiskSize-BookKeep	Data space