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（一）FAT32 文件系统将逻辑盘的空间划分为三部分，依次是引导区（BOOT区）、文件分配表区（FAT区）、数据区（DATA区）。引导区和文件分配表区又合称为系统区。

　　（二）引导区从第一扇区开始，使用了三个扇区，保存了该逻辑盘每扇区字节数，每簇对应的扇区数等等重要参数和引导记录。之后还留有若干保留扇区。而FAT16文件系统的引导区只占用一个扇区，没有保留扇区。

三）文件分配表区共保存了两个相同的文件分配表，因为文件所占用的存储空间（簇链）及空闲空间的管理都是通过FAT实现的，FAT如此重要，保存两个以便第一个损坏时，还有第二个可用。文件系统对数据区的存储空间是按簇进行划分和管理的，簇是空间分配和回收的基本单位，即，一个文件总是占用若干个整簇，文件所使用的最后一簇剩余的空间就不再使用，而是浪费掉了。
　　从统计学上讲，平均每个文件浪费0.5簇的空间，簇越大，存储文件时空间浪费越多，利用率越低。因此，簇的大小决定了该盘数据区的利用率。FAT16系统簇号用16位二进制数表示，从0002H到FFEFH个可用簇号(FFF0H到FFFFH另有定义,用来表示坏簇，文件结束簇等)，允许每一逻辑盘的数据区最多不超过FFEDH(65518)个簇。FAT32系统簇号改用32位二进制数表示，大致从00000002H到FFFFFEFFH个可用簇号。FAT表按顺序依次记录了该盘各簇的使用情况，是一种位示图法。
　　每簇的使用情况用32位二进制填写，未被分配的簇相应位置写零；坏簇相应位置填入特定值；已分配的簇相应位置填入非零值，具体为：如果该簇是文件的最后一簇，填入的值为FFFFFF0FH，如果该簇不是文件的最后一簇，填入的值为该文件占用的下一个簇的簇号，这样，正好将文件占用的各簇构成一个簇链，保存在FAT表中。0000000H、00000001H两簇号不使用，其对应的两个DWORD位置(FAT表开头的8个字节)用来存放该盘介质类型编号。FAT表的大小就由该逻辑盘数据区共有多少簇所决定，取整数个扇区。

　　（四）FAT32系统一簇对应8个逻辑相邻的扇区，理论上，这种用法所能管理的逻辑盘容量上限为16TB(16384GB)，容量大于16TB时，可以用一簇对应16个扇区，依此类推。FAT16系统在逻辑盘容量介于128MB到256MB时，一簇对应8个扇区，容量介于256MB到512MB时，一簇对应16个扇区，容量介于512MB到1GB时，一簇对应32个扇区，容量介于1GB到2GB时，一簇对应32个扇区，超出2GB的部分无法使用。显然，对于容量大于512MB的逻辑盘，采用FAT32的簇比采用FAT16的簇小很多，大大减少了空间的浪费。
　　但是，对于容量小于512MB的盘，采用FAT32虽然一簇8个扇区，比使用FAT16一簇16个扇区，簇有所减小，但FAT32的FAT表较大，占用空间较多，总数据区被减少，两者相抵，实际并不能增加有效存储空间，所以微软建议对小于512M的逻辑盘不使用FAT32。
　　另外，对于使用FAT16文件系统的用户提一建议，硬盘分区时，不要将分区(逻辑盘)容量正好设为某一区间的下限，例：将一逻辑盘容量设为1100M(稍大于1024M)，则使用时其有效存储容量比分区为950M的一般还少，因其簇大一倍，浪费的空间较多。还有，使用FDISK等对分区指定容量时，由于对1MB的定义不一样(标准的二进制的1MB为1048576B，有的系统将1MB理解为1000000B，1000KB等),及每个分区需从新磁道开始等因素，实际分配的容量可能稍大于指定的容量，亦需注意掌握。

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32-bit File Allocation Table

    The purpose of the FAT has not changed. It still acts as a table for linking the clusters of a file together. File/Directory entries point to the first cluster in the file which the operating system uses to find the first entry in the FAT. The FAT then tracks the location of the remaining clusters in the file. The entries are twice the size (4 bytes) and you can hold many more clusters on a FAT32 drive. 
    With the 16-bit FAT, the quantity of clusters on a drive is 65,525 (216 with 10 reserved). With a 32-bit FAT, the highest 4 bits of the 32-bit values are reserved and are not part of the cluster number. Therefore, the maximum amount of clusters on a 32-bit FAT is: 268,435,445 (228 with 10 reserved). 
    Stepping Through a FAT32 Entry 
    The starting cluster given in the file/directory entry tells the operating system where to find the first piece of that file. The starting cluster also tells the operating system where to look in FAT32 for the next cluster number. The entry for a starting cluster in a file entry is in bold below. 
     
    49 4F 20 20 20 20 20 20-44 4F 53 07 00 00 00 00 IO SYS..... 
    00 00 00 00 00 00 80 32-3E 1B 02 00 46 9F 00 00 .......2....F... 
     
    Two additional entries are used in the 32-bit directory entry. These two entries are taken from a reserved area and in this example are shown above as 00 00. Together with the existing 2 byte entry (02 00), there is a four-byte entry (00 00 00 02) to search the FAT. The following is a sample tracing of the file in a 32-bit FAT: 
     
    F8 FF FF 0F FF FF FF 0F-03 00 00 00 04 00 00 00 
    05 00 00 00 06 00 00 00-07 00 00 00 08 00 00 00 
    09 00 00 00 0A 00 00 00-0B 00 00 00 0C 00 00 00 
    0D 00 00 00 0E 00 00 00-0F 00 00 00 10 00 00 00 
    11 00 00 00 12 00 00 00-13 00 00 00 14 00 00 00 
    15 00 00 00 16 00 00 00-17 00 00 00 18 00 00 00 
    19 00 00 00 1A 00 00 00-1B 00 00 00 FF FF FF F8 
     
    As with FAT16, F8 is the media descriptor byte. The next 7 bytes, FF FF 0F FF FF FF 0F, are reserved. The clusters are grouped in 4 byte numbers as: 
     
    03 00 00 00, 04 00 00 00, 05 00 00 00, 06 00 00 00 
     
    And so on. Invert the numbers to read: 
     
    00 00 00 03, 00 00 00 04, 00 00 00 05, 00 00 00 06 
     
    And so on, to trace the file through the FAT. (The contents in the second entry is 00 00 00 03. F8 FF FF FF, and FF FF FF 0F are grouped as entries 0 and 1 respectively.) The new end of file marker is FF FF FF F8. 
    How Win.com Determines Improper Shutdown 
    Of the first 112 bytes of the FAT32, the first 8 bytes are reserved. The eighth byte of the reserved area, by default, is 0F. The virtual file allocation table (VFAT) and the Windows 98 shutdown process manipulate the fourth bit of this byte to 1 or 0. 
    

    
0 = VFAT has written to disk 
    
1 = Windows has properly shutdown 
    

    When you write a file to the disk, VFAT handles the write. During the write, VFAT clears the fourth bit to 0 (07h). When Windows 98 exits properly, this bit is reset to 1. During reboot, Win.com reads that bit. If it is set to 0, it runs ScanDisk to check the drive for errors. 
    Hard Sector Error. Windows 98 detects a hard sector error during startup. This process toggles the third bit to zero (0Bh). When detected during startup, Windows 98 automatically launches ScanDisk with a surface scan test. 
    Disabling ScanDisk at Boot. There is a way to disable the improper shutdown check. It is in the Msdos.sys file under [OPTIONS]. The parameters for AutoScan are as follows: 
     
    Value Definition 
     
    AUTOSCAN = 0 Ignore the bits in the reserved FAT entry 
    AUTOSCAN = 1 Default behavior, run ScanDisk 
    Mirroring 
    On all FAT drives, historically, there are two copies of the FAT. If an error occurs reading the primary copy, the file system will attempt to read from the backup copy. On 12-bit and 16-bit FAT drives, the first FAT is always the primary copy and a modification is automatically written to the second copy. When a second FAT is written to as a backup, the process is called mirroring. 
    On new FAT32 drives, mirroring a secondary FAT can be disabled. This means that a read/write is quicker using one FAT, or if the first FAT is sitting on corrupted sectors, the second FAT can be used as a primary with the first FAT ignored. 
    Note On FAT32 drives, a FAT can be very large. Disabling duplicate FAT writes can make FAT access quicker. Windows 98 does not provide a mechanism for eliminating the use of a second FAT. Mirroring is always enabled. Third-party utilities, however, might include this ability as users with larger hard disks might want to disable a second FAT to speed disk access. Any issues about mirroring should be directed to that third-party utility. 
    Root Directory 
    With FAT32, the limitation is now 65,535 root directory entries. 
    There is a new entry in the Boot Sector that points to the first cluster of the root directory. The root directory is no longer forced to reside at a specific location after the second FAT and it can grow just like a subdirectory. 
    There is a trade off in performance when you have a large number of directory entries to pass across when searching for actual data. For this reason, it is recommended that you limit the number of root directory entries to a small, manageable number. There is no actual recommended size for the same reasons as there is no optimal cluster size to choose from. 
    Extensions Changed, Superseded, or No Longer Supported 
    The following list presents some areas where FAT32 may be incompatible with legacy software: 
    

    
Share services are a part of the installable file system (IFS) manager. VFAT uses them to provide full file sharing functionality. All MS-DOS-based, Win16-based, and Win32-based applications have full file sharing services available to them. As a consequence, the MS-DOS utility Share.exe is no longer necessary and is not provided in Windows 98. 
    
VFAT implements an enhanced version of FASTOPEN. As such, the MS-DOS FASTOPEN utility is no longer necessary, but can install without error. 
    
Windows 3.x File Manager is not supported since it may misreport free or total disk space. 
    
File Control Block (FCB) has limited support but this should not be a problem. 
    
Dealing with files larger than 2 GB (opening, creating, writing) may cause problems on non-FAT32-aware programs. 
    
Absolute disk reads and write utilities should be upgraded to recognize FAT32. 
    
Users should not dual-boot Windows 98 with FAT32 and Windows NT 4.0. 
    
Interlink does not work on FAT32. 
    

    
Windows 98 partition types not recognized by Windows NT.

    When you set up Windows NT on a computer that has Windows 98 preinstalled, the FAT partitions may be shown as unknown. 
    Windows NT cannot recognize primary partitions using the FAT32 format. Backup any data that you might need to save and then delete the partition(s) using Fdisk from either MS-DOS or Windows 98. 
    Windows 98 supports four partition types for FAT file systems that Windows NT cannot recognize. The partition type can be identified by the System ID byte in the partition table. This byte is located at the following offsets: 
     
    0x1C2 = Partition 1 
    0x1D2 = Partition 2 
    0x1E2 = Partition 3 
    0x1F2 = Partition 4 
     
     
    The four values used by Windows 98 that Windows NT does not recognize are as follows: 
     
    0x0B Primary Fat32 Partitions up to 2047 GB 
    0x0C Same as 0x0B, uses Logical Block Address Int 0x13 extensions 
    0x0E Same as 0x06, uses Logical Block Address Int 0x13 extensions 
    0x0F Same as 0x05, uses Logical Block Address Int 0x13 extensions 
     
    The FAT partition types that Windows NT version 3.x and 4.0 can recognize are: 
     
    0x01 Fat12 < 10 megabytes 
    0x04 Fat16 < 32 megabytes 
    0x06 Fat16 > 32 megabytes 
    0x05 Extended (may be FAT, HPFS or NTFS) 
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