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首页Microsoft exFat规范说明.pdf
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目录
1. exFAT vs. FAT32 Comparison ............................................................................................. 2
2. Volume Layout .................................................................................................................. 3
3. Boot Sector ........................................................................................................................ 5
4. OEM Parameters ............................................................................................................... 8
5. File Allocation Table (FAT) ................................................................................................ 10
6. Allocation Bitmap ............................................................................................................ 12
7. Up-case Table .................................................................................................................. 13
7.1 Mandatory First 128 Up-case Table Entries .................................................. 14
7.2 Mandatory First 128 Up-case Table Entries in compressed format ........ 14
8. Directory Structure .......................................................................................................... 16
8.1. Generic Directory Entry Template .................................................................................... 16
8.2. Generic Primary Directory Entry Template ...................................................................... 17
8.3 Generic Secondary Directory Entry Template ................................................................ 18
8.4 Defined Directory Entries .................................................................................................. 19
8.5 Allocation Bitmap Directory Entry ..................................................................................... 19
8.6 Up-Case Table Directory Entry .......................................................................................... 20
8.7 Volume Label Directory Entry ........................................................................................... 21
8.8 File Directory Entry ............................................................................................................ 21
9. Timestamp Format .......................................................................................................... 23
10. Volume GUID Directory Entry ..................................................................................... 25
10.1 TexFAT Padding Directory Entry ........................................................................... 25
10.2 Windows CE Access Control Table Directory Entry ........................................... 25
10.3 Stream Extension Directory Entry......................................................................... 25
10.4 File Name Directory Entry ...................................................................................... 27
11. Invalid File Name Characters ....................................................................................... 28

1. exFAT vs. FAT32 Comparison
Feature
FAT32
exFAT
Maximum Volume Size
8 TB*
128 PB
Maximum File Size
4 GB
16 EB
Maximum Cluster Size
32 KB **
32 MB
Maximum Cluster Count
2
28
2
32
Maximum File Name Length
255
255
Date/Time resolution
2 s
10 ms
MBR Partition Type Identifier
0x0B, 0x0C
0x07
* Windows cannot format FAT32 volumes bigger than 32GB, though itsupports larger
volumes created by third party implementations; 16 TB is the maximum volume size if
formatted with 64KB cluster
** According to Microsoft KB184006 clusters cannot be 64KB or larger, though some third
party implementations support up to 64KB.

2. Volume Layout
Offset, sectors
Size, sectors
Block
Comments
Main Boot Region
0
1
Boot Sector
1
8
Extended
Boot Sectors
9
1
OEM
Parameters
10
1
Reserved
11
1
Boot
Checksum
Backup Boot Region
12
1
Boot Sector
13
8
Extended
Boot Sectors
21
1
OEM
Parameters
22
1
Reserved
23
1
Boot
Checksum
FAT Region
24
FatOffset - 24
FAT
Alignment
Boot Sectors
contain
FatOffset
FatOffset
FatLength
First FAT
Boot Sectors
contain
FatOffset

and
FatLength
FatOffset + FatLength
FatLength
Second FAT
For TexFAT
only
Data Region
FatOffset + FatLength *
NumberOfFats
ClusterHeapOffset – (FatOffset
+ FatLength * NumberOfFats)
Cluster
Heap
Alignment
ClusterHeapOffset
ClusterCount *
2^SectorsPerClusterShift
Cluster
Heap
ClusterHeapOffset +
ClusterCount *
2^SectorsPerClusterShift
VolumeLength –
(ClusterHeapOffset +
ClusterCount *
2^SectorsPerClusterShift)
Excess
Space

3. 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 * ↓
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