Network, Computer and Programming Resources
Boot Sector and BPB Structure[Fat12 and Fat16]-> BS_BootSig [Offset=38, Size=1]Boot Sector and BPB Structure[Fat12 and Fat16]-> BS_DrvNum [Offset=36, Size=1]Boot Sector and BPB Structure[Fat12 and Fat16]-> BS_FilSysType [Offset=54, Size=8]Boot Sector and BPB Structure[Fat12 and Fat16]-> BS_Reserved1 [Offset=37, Size=1]Boot Sector and BPB Structure[Fat12 and Fat16]-> BS_VolID [Offset=39, Size=4]Boot Sector and BPB Structure[Fat12 and Fat16]-> BS_VolLab [Offset=43, Size=11]Boot Sector and BPB Structure[Fat32]-> BPB_BkBootSec [Offset=50, Size=2]Boot Sector and BPB Structure[Fat32]-> BPB_ExtFlags [Offset=40, Size=2]Boot Sector and BPB Structure[Fat32]-> BPB_FATSz32 [Offset=36, Size=4]Boot Sector and BPB Structure[Fat32]-> BPB_FSInfo [Offset=48, Size=2]Boot Sector and BPB Structure[Fat32]-> BPB_FSVer [Offset=42, Size=2]Boot Sector and BPB Structure[Fat32]-> BPB_Reserved [Offset=52, Size=12]
Fat32 - Boot Sector and BPB Structure[Fat12 and Fat16]-> BS_FilSysType [Offset=54, Size=8]
One of the strings “FAT12 ”, “FAT16 ”, or “FAT ”. NOTE: Many people think that the string in this field has something to do with the determination of what type of FAT—FAT12, FAT16, or FAT32—that the volume has. This is not true. You will note from its name that this field is not actually part of the BPB. This string is informational only and is not used by Microsoft file system drivers to determine FAT typ,e because it is frequently not set correctly or is not present. See the FAT Type Determination section of this document. This string should be set based on the FAT type though, because some non-Microsoft FAT file system drivers do look at it.