Boot Sector

Offset

Size

Description

Comments

0 (0x00)

3

JumpBoot

0xEB7690

3 (0x03)

8

FileSystemName

"EXFAT>

11 (0x0B)

53

MustBeZero

 

64 (0x40)

8

PartitionOffset

In sectors; if 0, shall be ignored

72 (0x48)

8

VolumeLength

Size of exFAT volume in sectors

80 (0x50)

4

FatOffset

In sectors

84 (0x54)

4

FatLength

In sectors. May exceed the required space in order to align the second FAT

88 (0x58)

4

ClusterHeapOffset

In sectors

92 (0x5C)

4

ClusterCount

2^32-11 is the maximum number of clusters could be described

96 (0x60)

4

RootDirectoryCluster

 

100 (0x64)

4

VolumeSerialNumber

 

104 (0x68)

2

FileSystemRevision

as MAJOR.minor, major revision is high byte, minor is low byte; currently 01.00

106 (0x6A)

2

VolumeFlags * ↓

 

Offset

Size

Field

0 1

ActiveFat 0 - First FAT and Allocation Bitmap are active, 1- Second.

1 1

VolumeDirty (0-clean, 1-dirty)

2 1

MediaFailure (0 – no failures reported or they already marked as BAD clusters) 1- some read/write operations failed)

3 1

ClearToZero (no meaning)

4 12

Reserved (no meaning)

108 (0x6C)

1

BytesPerSectorShift

Power of 2. Minimum 9 (512 bytes per sector), maximum 12 (4096 bytes per sector)

109 (0x6D) 1

SectorsPerCluster Shift

Power of 2. Minimum 0 (1 sector per cluster), maximum 25 – BytesPerSectorShift, so max cluster size is 32 MB

110 (0x6E)

1

NumberOfFats

2 is for TexFAT only

111 (0x6F) 1

DriveSelect

Extended INT 13h drive number; typically 0x80

112 (0x70)

1

PercentInUse

0..100 – percentage of allocated clusters rounded down to the integer 0xFF – percentage is not available

113 (0x71) 7

Reserved

 

120 (0x78)

390

BootCode

 

510 (0x1FE) 2

BootSignature

0xAA55

512 (0x200)

2^BytesPerSectorShift - 512

ExcessSpace

Not used

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