FAT16文件系统解析（C#版本）

public class DiskBase
...{
    ...#region 
    public struct PartitionTable
    ...{
        public byte BootFlag;            //分区活动标志 只能选00H和80H。80H为活动，00H为非活动
        public CHS StartCHS;             //分区开始的柱面、磁头、扇区  
        public byte SystemID;            //分区类型  01 FAT32  04 FAT16<32M  06 FAT16 07 HPFS/NTFS  05 0F 扩展分区
        public CHS EndCHS;               //分区结束的柱面、磁头、扇区  
        public UInt32 RelativeSectors;   //分区起始扇区数，指分区相对于记录该分区的分区表的扇区位置之差 (该分区表：LBA=0x0)。 
        public UInt32 TotalSectors;      //分区总扇区数 
    }
    public struct CHS
    ...{
        public byte Head;                //磁头
        public byte Sector;              //扇区 六位
        public UInt16 Cylinder;          //柱面 十位
    }
    public struct MBR
    ...{
        public byte[] bytBootCode;       //ofs:0.引导代码446字节 "FA 33 C0 8E D0 BC…"
        public PartitionTable[] PT;      //ofs:446.64个字节 分区表 length=4*16
        public UInt16 EndingFlag;        //ofs:510.结束标识:0xAA55。

        public MBR(byte[] bytData)
        ...{
            int i;
            bytBootCode = new byte[446];
            for (i = 0; i < 446; i++) bytBootCode[i] = bytData[i];

            PT = new PartitionTable[4];
            for (i = 0; i < 4; i++)
            ...{
                PT[i].BootFlag = bytData[446 + i * 16 + 0];
                PT[i].StartCHS.Head = bytData[446 + i * 16 + 1];
                PT[i].StartCHS.Sector = (byte)(bytData[446 + i * 16 + 2] & 0x3f);
                PT[i].StartCHS.Cylinder = (UInt16)(((bytData[446 + i * 16 + 2] & 0xc0) << 2) | bytData[446 + i * 16 + 3]);
                PT[i].SystemID = bytData[446 + i * 16 + 4];
                PT[i].EndCHS.Head = bytData[446 + i * 16 + 5];
                PT[i].EndCHS.Sector = (byte)(bytData[446 + i * 16 + 6] & 0x3f);
                PT[i].EndCHS.Cylinder = (UInt16)(((bytData[446 + i * 16 + 6] & 0xc0) << 2) | bytData[446 + i * 16 + 7]);
                PT[i].RelativeSectors = (UInt32)(bytData[446 + i * 16 + 11] << 24 | bytData[446 + i * 16 + 10] << 16 | bytData[446 + i * 16 + 9] << 8 | bytData[446 + i * 16 + 8]);
                PT[i].TotalSectors = (UInt32)(bytData[446 + i * 16 + 15] << 24 | bytData[446 + i * 16 + 14] << 16 | bytData[446 + i * 16 + 13] << 8 | bytData[446 + i * 16 + 12]);
            }
            EndingFlag = (UInt16)(bytData[510] << 8 | bytData[511]);
        }

    #endregion        

    //系统引导记录（兼容FAT16和FAT32）#region     //系统引导记录（兼容FAT16和FAT32）
    public struct DBR
    ...{
        public byte[] BS_JmpBoot;            //ofs:0.典型的如：0xEB,0x3E,0x90。
        public byte[] BS_OEMName;            //ofs:3.典型的如：“MSWIN4.1”。 
        public UInt16 BPB_BytsPerSec;        //ofs:11.每扇区字节数。 
        public byte BPB_SecPerClus;          //ofs:13.每簇扇区数。 
        public UInt16 BPB_RsvdSecCnt;        //ofs:14.保留扇区数，从 DBR到 FAT的扇区数。
        public byte BPB_NumFATs;             //ofs:16.FAT的个数。 
        public UInt16 BPB_RootEntCnt;        //ofs:17.根目录项数。 
        public UInt16 BPB_TotSec16;          //ofs:19.分区总扇区数(<32M时用)。 
        public byte BPB_Media;               //ofs:21.分区介质标识,优盘一般用 0xF8。 
        public UInt16 BPB_FATSz16;           //ofs:22.每个 FAT占的扇区数。 
        public UInt16 BPB_SecPerTrk;         //ofs:24.每道扇区数。 
        public UInt16 BPB_NumHeads;          //ofs:26.磁头数。 
        public UInt32 BPB_HiddSec;           //ofs:28.隐藏扇区数，从 MBR到 DBR的扇区数。 
        public UInt32 BPB_TotSec32;          //ofs:32.分区总扇区数(>=32M时用)。

        //---------------------
        //FAT32特有
        public UInt32 BPB_FATSz32;          //ofs:36.每个 FAT占的扇区数。
        public UInt16 BPB_ExtFlags;         //ofs:40.FAT标志
        public UInt16 BPB_FSVer;            //ofs:42.版本号 高字节主版本 低字节次版本号
        public UInt32 BPB_RootClus;         //ofs:44.根目录所在第一个簇的簇号，通常该数值为2，但不是必须为2。
        public UInt16 BPB_FSInfo;           //ofs:48.保留区中FAT32 卷FSINFO 结构所占的扇区数，通常为1。
        public UInt16 BPB_BkBootSec;        //ofs:50.如果不为0，表示在保留区中引导记录的备份数据所占的扇区数，通常为6。同时不建议使用6 以外的其他数值。
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 12)]
        public byte[] BPB_Reserved;         //ofs:52.备用     

        //---------------------
        public byte BS_drvNum;              //ofs:64/36.软盘使用 0x00,硬盘使用 0x80。 
        public byte BS_Reserved1;           //ofs:65/37.保留。 
        public byte BS_BootSig;             //ofs:66/38.扩展引导标记：0x29。 
        public byte[] BS_VolID;             //ofs:67/39.盘序列号。
        public byte[] BS_VolLab;            //ofs:71/43.“Msdos      ”。 
        public byte[] BS_FilSysType;        //ofs:82/54.“FAT32   ”。 
        public byte[] ExecutableCode;       //ofs:90/62.引导代码。 
        public UInt16 EndingFlag;           //ofs:510.结束标识:0xAA55。

        //---------------------
        //0-未知 1-FAT12 2-FAT16 3-FAT32 其它值为未知
        public byte FATType;

        //获取信息
        public DBR(byte[] bytData)
        ...{
            FATType = IsType(bytData);
            int i;
            BS_JmpBoot = new byte[3];
            for (i = 0; i < 2; i++) BS_JmpBoot[i] = bytData[i];
            BS_OEMName = new byte[8];
            for (i = 0; i < 8; i++) BS_OEMName[i] = bytData[i + 3];
            BPB_BytsPerSec = (UInt16)(bytData[12] << 8 | bytData[11]);
            BPB_SecPerClus = bytData[13];
            BPB_RsvdSecCnt = (UInt16)(bytData[15] << 8 | bytData[14]);
            BPB_NumFATs = bytData[16];
            BPB_RootEntCnt = (UInt16)(bytData[18] << 8 | bytData[17]);
            BPB_TotSec16 = (UInt16)(bytData[20] << 8 | bytData[19]);
            BPB_Media = bytData[21];
            BPB_FATSz16 = (UInt16)(bytData[23] << 8 | bytData[22]);
            BPB_SecPerTrk = (UInt16)(bytData[25] << 8 | bytData[24]);
            BPB_NumHeads = (UInt16)(bytData[27] << 8 | bytData[26]);
            BPB_HiddSec = (UInt32)(bytData[31] << 24 | bytData[30] << 16 | bytData[29] << 8 | bytData[28]);
            BPB_TotSec32 = (UInt32)(bytData[35] << 24 | bytData[34] << 16 | bytData[33] << 8 | bytData[32]);
            //----------
            if (FATType == 3)
            ...{
                //FAT32
                BPB_FATSz32 = (UInt32)(bytData[39] << 24 | bytData[38] << 16 | bytData[37] << 8 | bytData[36]);
                BPB_ExtFlags = (UInt16)(bytData[41] << 8 | bytData[40]);
                BPB_FSVer = (UInt16)(bytData[43] << 8 | bytData[42]);
                BPB_RootClus = (UInt32)(bytData[47] << 24 | bytData[46] << 16 | bytData[45] << 8 | bytData[44]);
                BPB_FSInfo = (UInt16)(bytData[49] << 8 | bytData[48]);
                BPB_BkBootSec = (UInt16)(bytData[51] << 8 | bytData[50]);
                BPB_Reserved = new byte[12];
                for (i = 0; i < 12; i++) BPB_Reserved[i] = bytData[i + 52];
                //----------
                BS_drvNum = bytData[64];
                BS_Reserved1 = bytData[65];
                BS_BootSig = bytData[66];
                BS_VolID = new byte[4];
                for (i = 0; i < 4; i++) BS_VolID[i] = bytData[67 + i];
                BS_VolLab = new byte[11];
                for (i = 0; i < 11; i++) BS_VolLab[i] = bytData[71 + i];
                BS_FilSysType = new byte[8];
                for (i = 0; i < 8; i++) BS_FilSysType[i] = bytData[82 + i];
                ExecutableCode = new byte[420];
                for (i = 0; i < 420; i++) ExecutableCode[i] = bytData[90 + i];
            }
            else
            ...{
                //FAT16
                BS_drvNum = bytData[36];
                BS_Reserved1 = bytData[37];
                BS_BootSig = bytData[38];
                BS_VolID = new byte[4];
                for (i = 0; i < 4; i++) BS_VolID[i] = bytData[39 + i];
                BS_VolLab = new byte[11];
                for (i = 0; i < 11; i++) BS_VolLab[i] = bytData[43 + i];
                BS_FilSysType = new byte[8];
                for (i = 0; i < 8; i++) BS_FilSysType[i] = bytData[54 + i];
                ExecutableCode = new byte[448];
                for (i = 0; i < 448; i++) ExecutableCode[i] = bytData[62 + i];

                //FAT32
                BPB_FATSz32 = 0;
                BPB_ExtFlags = 0;
                BPB_FSVer = 0;
                BPB_RootClus = 0;
                BPB_FSInfo = 0;
                BPB_BkBootSec = 0;
                BPB_Reserved = new byte[12];
            }
            //----------
            EndingFlag = (UInt16)(bytData[510] << 8 | bytData[511]);
        }
    #endregion

    //文件系统判断（采用微软的判断方法）        
    public static byte IsType(byte[] bytData)
    ...{
        //不是合法BPB扇区数据
        if (bytData[510] != 0x55 || bytData[511] != 0xaa) return 0;

        //跳转指令不合法
        if (bytData[0] != 0xeb && bytData[0] != 0xe9) return 0;

        //每扇区包含的字节数（一般为512个字节）
        UInt16 BPB_BytsPerSec = (UInt16)(bytData[12] << 8 | bytData[11]);

        //仅处理512个字节的扇区
        if (BPB_BytsPerSec != 512) return 0;

        //每簇扇区数
        byte BPB_SecPerClus = bytData[13];
        //保留扇区数
        UInt16 BPB_RsvdSecCnt = (UInt16)(bytData[15] << 8 | bytData[14]);
        //FAT表的个数
        byte BPB_NumFATs = bytData[16];

        //FAT表的个数必须为2
        if (BPB_NumFATs != 2) return 0;

        //根目录项数(32字节为单位)
        UInt16 BPB_RootEntCnt = (UInt16)(bytData[18] << 8 | bytData[17]);
        //分区总扇区数(<32M时用)
        UInt16 BPB_TotSec16 = (UInt16)(bytData[20] << 8 | bytData[19]);
        //每个FAT占的扇区数
        UInt16 BPB_FATSz16 = (UInt16)(bytData[23] << 8 | bytData[22]);
        //分区总扇区数(>=32M时用)
        UInt32 BPB_TotSec32 = (UInt32)(bytData[35] << 24 | bytData[34] << 16 | bytData[33] << 8 | bytData[32]);
        //每个FAT占的扇区数(FAT32)
        UInt32 BPB_FATSz32 = (UInt32)(bytData[39] << 24 | bytData[38] << 16 | bytData[37] << 8 | bytData[36]);

        UInt64 FATSz = 0, TotSec = 0, DataSec = 0;
        UInt64 RootDirSectors = (UInt64)(((BPB_RootEntCnt * 32) + (BPB_BytsPerSec - 1)) / BPB_BytsPerSec);

        if (BPB_FATSz16 != 0)
            FATSz = BPB_FATSz16;
        else
            FATSz = BPB_FATSz32;

        if (BPB_TotSec16 != 0)
            TotSec = BPB_TotSec16;
        else
            TotSec = BPB_TotSec32;

        DataSec = TotSec - (BPB_RsvdSecCnt + (BPB_NumFATs * FATSz) + RootDirSectors);
        UInt64 CountofClusters = DataSec / BPB_SecPerClus;
        if (CountofClusters < 4085)
        ...{
            /**//* FAT 类型是FAT12 */
            return 1;
        }
        else if (CountofClusters < 65525)
        ...{
            /**//* FAT 类型是FAT16 */
            return 2;
        }
        else
        ...{
            /**//* FAT 类型是FAT32*/
            return 3;
        }
    }           
}