Windows NT FAT16 Size Limitations

    Windows NT (3.5, 3.51 and 4.0), Windows 2000 and Windows XP all support the creation of primary partitions and logical drives up to 4GB, using the FAT16 file system. This 4GB partition limit is imposed by the maximum number of clusters (64K) and the largest supported cluster size. For the Window NT family of operating systems, the FAT16 cluster size limited is 64KB (instead of 32KB), so:

64K x 64 KB = 4096 MB = 4 GB

    FAT16 volumes larger than 2GB are not reliably accessible from computers running Windows Me/98/95 or MS-DOS. The size limit for FAT16 volumes in these operating systems is 2GB. (The cluster size is limited to 32KB, instead of 64KB.) So to maintain compatibility, a FAT16 volume cannot be larger than 2GB.

[Webpage Copy or 'Mirror']Problems Accessing FAT16 Over 2.0GB
Source: Microsoft Knowledge Base Article 127851

    Further, the size of the boot partition generated by Windows NT setup is limited to 4GB, because Windows NT setup must first format the partition as FAT. And although it is possible to select NTFS for the boot partition during setup, such a partition is still formatted first as FAT, then converted to NTFS. This does not apply to Windows 2000 and Windows XP, which both directly format the boot partition using the chosen file system.

[Webpage Copy or 'Mirror']Windows NT Boot Partition Size limits
Source: Microsoft Knowledge Base Article 119497

    For the Windows NT family of operating systems, the FAT file system uses the following cluster sizes:

  Drive Size          FAT Type   Sectors       Cluster
 (logical volume)                Per Cluster   Size
 ------------------   --------   -----------   -------
    0 MB - 15 MB       12-bit     8             4K
   16 MB - 127 MB      16-bit     4             2K
  128 MB - 255 MB      16-bit     8             4K
  256 MB - 511 MB      16-bit     16            8K
  512 MB - 1023 MB     16-bit     32            16K
 1024 MB - 2048 MB     16-bit     64            32K
 2048 MB - 4096 MB     16-bit     128           64K
*4096 MB - 8192 MB     16-bit     256           128K  NT V4.0 only
*8192 MB - 16384 MB    16-bit     512           256K  NT V4.0 only

* To support > 4GB FAT partitions using 128k or 256k clusters, the drives must use > 512 byte sectors.

Note: Increasing the "standard" 512 Byte sector size, to exceed 4GB using FAT16, is just asking for many things to not work . . . sort of like Windows Me/98/95 has problems using a drive with greater than 32KB clusters, to exceed 2GB using FAT16.

Sources: Microsoft Knowledge Base Articles - Q310561, Q140365, Q119497

Related Information:

[HTML format Notes]FAT16 Logical Drive Size
. . . 2.00GB (2.15 billion Bytes) limit.
For Windows Me/98/95 and MS-DOS, the maximum size for a primary FAT16 partition or a logical FAT16 partition is 2GB. While the possible dramatic increase in "wasted" drive space, resulting from larger cluster sizes, also needs consideration.
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Page Content Updated: 12 June 2005