FAT 32 is a disk file allocation system from Microsoft that uses 32-bit values for FAT entries

FAT 32 is a disk file allocation system from Microsoft that uses 32-bit values for FAT entries
instead of 16-bit values used by the original FAT system, enabling partition sizes up to 2TB
(terabytes). FAT32 first appeared in Windows 95B and is also found in Windows 98 and
Windows NT 5.0.
In order to overcome the volume size limit of FAT16 while still allowing memory-constrained
DOS real-mode code to handle the format, Microsoft decided to implement a newer generation of
FAT, known as FAT32, with 32-bit cluster numbers, of which 28 bits are currently used.
In theory, this should support a total of approximately 268,435,438 (< 228) clusters, allowing for
drive sizes in the range of 2 terabytes. However, due to limitations in Microsoft's scandisk utility,
the FAT is not allowed to grow beyond 4,177,920 (< 224) clusters, placing the volume limit at
124.55 gigabytes, unless “scandisk” is not needed. Windows 2000 and XP placed a limit on the
size of FAT32 partitions they can create at 32 GB, Microsoft says this is by design but does not
explain why, and those versions of Windows are quite capable of reading and writing larger
FAT32 partitions created by other means. FAT32 was introduced with Windows 95 OSR2. The
many changes it incorporated made it a major improvement.
The maximum possible file size for a FAT32 volume is 4 GB minus 1 byte (232-1 bytes). For most
users, this has become the most nagging limit of FAT32 as of 2005, since video capture and
editing applications can easily exceed this limit, as can the system swap file.
32-bit File Allocation Table File System Not the same as VFAT or FAT, which are both 16-bit file
systems.
DIR
Means Directory, also called FDT，File Directory Table. DIR is the root sector, following after
the second FAT (backup FAT). It records each start cell, files. Operation system can locate files
according to the outset of FAT and FAT.
DATA
DATA area is the real place where data is stored. It is after DIR, covering the most space of hard
disk.
The location of the 5 areas is as following:
Usually, MBR covers 63 sectors (actually it covers only one); DBR covers 32 sectors (actually it
covers the first and the sixth sectors. The first sector works while the sixth is backup of the first);
FAT1=FAT2. The length of FAT will change according to the size of partition and the number of
sectors. DIR changes the most. In early time system, DIR has fixed length of 32 sectors while each
file directory covers 32 bytes. As a result, there are at most 512 items under root directory. Floppy
disk can only contain 112 items, or there would be no file or directory created under root directory.
Afterward, the limitation is broken. From then on, there will be no single root directory, which
becomes part of DATA. Even, root directory files are not right after FAT. They can be in any
position in DATA.