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Functional Description
Table 26-25. FAT Boot Sector (continued)
Offset Length[bytes] Name Description
For FAT12/16, number of 32 bytes entries
in the Root Directory (multiple of
0011h 2 BPB_RootEntCnt
BPB_BytsPerSec/32)For FAT32 this value
is 0
Total Count of sectors on the volume. If
the size is bigger than 10000h or for
0013h 2 BPB_TotSec16
FAT32, this field is 0 and BPB_TotSec32
holds the value
Media Type, usually F8h: fixed, non-
0015h 1 BPB_Media
removable
For FAT12/16, size in sectors of one
0016h 2 BPB_FATSz16
FATFor FAT32, holds 0
Number of sectors per track, 63 for
0018h 2 BPB_SecPerTrk
SD/MMC
001Ah 2 BPB_NumHeads Number of heads, 255 for SD/MMC
Number of sectors preceeding the
001Ch 4 BPB_HiddSec
partition
Total Count of sectors on the volume. If
the size is smaller than 10000h (for
0020h 4 BPB_TotSec32
FAT12/16), this field is 0 and
BPB_TotSec16 is valid
0024h 1 BS_DrvNum Drive Number
0025h 1 BS_Reserved1 00h
Extended Boot Signature 29h. Indicates
0026h 1 BS_BootSig
that the following 3 fields are present
0027h 4 BS_VolID Volume Serial Number
FAT12/16
002Bh 11 BS_VolLab Volume Label
File system Type: “FAT12”, “FAT16”,
“FAT32”.Note: This field is not mandatory
0036h 8 BS_FilSysType
(i.e BS_) therefore it cannot be used to
indentify the partition type.
4137
SPRUH73H–October 2011–Revised April 2013 Initialization
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