Summary of FAT file system 2
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四、 分区引导扇区 Fourth, the district cited guide sector Often called the boot sector, Microsoft called sector 0 (0 th Sector), we know by the previous description, called sector 0 is not correct, so it is easy to misunderstand the most disk in front of a sector, sector 0 just call it the FAT sector indicates that it is a reference point only. Figure 2：DBR
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offset
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Length
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Description
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（byte） （byte）
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BS_jmpBoot
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0x00
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3
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Jump instruction, pointing to the boot code
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BS_OEMName
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0x03
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8
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The recommended value "MSWIN4.1". Some vendors might FAT drive
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Detect this, so set "MSWIN4.1" You can try to avoid compatibility
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Problems
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BPB_BytsPerSec
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0x0b
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2
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The number of bytes per sector, only the following values: 512, 1024,
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2048 or 4096. Set 512 will get the best compatibility, the current
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There are a lot of FAT code is mandatory for the number of bytes per sector 512,
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Instead of the actual detection value. But Microsoft's operating system can be a good support
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BPB_SecPerClus
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0x0d
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1
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1024, 2048 or 4096
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Number of sectors per cluster, its value must be integer power of 2 (the integer must
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> = 0), but also to ensure that the number of bytes per cluster can not exceed 32K, it
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1024 * 32 bytes
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BPB_RsvdSecCnt
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0x0e
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2
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The number of reserved sectors of this field can not be 0, FAT12/FAT16 must
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1, a typical value of FAT32 is taken as 32, Microsoft's system to support any non-zero
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Value
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BPB_BumFATs
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0x10
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1
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Copies FAT partition tables, FAT formats are any suggestions for 2
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BPB_RootEntCnt
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0x11
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2
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For FAT12 and FAT16 this domain number (each directory that contains the root directory
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Term length is 32bytes), for FAT32, this must be 0. To
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In FAT12 and FAT16, this number must be multiplied by 32 to
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BPB_BytesPerSec even multiple of, in order to achieve better compatibility,
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FAT12 and FAT16 should be a value of 512
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BPB_ToSec16
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0x13
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2
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Early versions of 16bit total sector, where the total number of sectors, including FAT volumes
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All sectors on the four basic partitions, this field can be 0, if this field is 0,
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So BPB_ToSec32 must be 0 for FAT32, this field will be 0.
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For FAT12/FAT16, fill in the total number of sectors in this field, if the value is less than
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0x10000 words, BPB_ToSec32 must be 0
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BPB_Media
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0x15
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1
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For "fixed" (non-removable) storage media, 0xF8 standard
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Values for the removable storage medium, is frequently used value 0xF0, this
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The value domain can legally take 0xF0, 0xF8, 0xF9, 0xFA, 0xFC,
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0xFD, 0xFE, 0xFF. Also to be reminded that, regardless of the domain written
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What values must also be in FAT [0] is the low byte written to the same
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Value, which is used as the early MSDOS 1.x byte to determine what is
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Kinds of storage media
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BPB_FATSz16
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0x16
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2
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FAT12/FAT16 a number of sectors occupied by the FAT table for FAT32
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For this field must be 0, specified in the FAT table in BPB_FATZ32
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Size
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BPB_SecPerTrk
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0x18
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2
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The number of sectors per track for BIOS interrupt 0x13, this field only to have
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"Special Shapes" (by the cylinder head and each track is divided into a number of) storage
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Media effectively, and must be able to invoke the BIOS interrupt 0x13 to get this
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Value
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BPB_NumHeads
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0x1A
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2
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Heads, 0x13 for BIOS interrupts, similar to the above BPB_
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SecPerTrk, only for special media to be effective, this field contains a to
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Is a small value, for example, 1,4 M This field is two floppy
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BPB_HidSec
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0x1C
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4
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Previously hidden FAT partition number of sectors, we must make the call BIOS
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The 0x13 interrupt can get this value, for those who do not partition storage
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Media, this field must be 0, of what value is determined by the specific use of the operating system
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BPB_ToSec32
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0x20
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4
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The volume of the total number of sectors (32bit), where the total number of sectors, including FAT volumes
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Four basic points of all sectors, this field can be 0, if this field is 0,
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BPB_ToSec16 must be non-zero for FAT32, this field must be non-zero.
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For FAT12/FAT16 If the total number of sectors is greater than or equal to 0x10000
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, Then this field is the total number of sectors, while BPB_ToSec16 is 0.
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