Information Technology Reference
In-Depth Information
Inside a FAT32 Volume
FAT32 is an option for larger media that can't use FAT16. A FAT32 system
has other advantages as well, such as no limit on root-directory size and the
availability of additional information for use in repairing damaged media
and finding free clusters quickly. Compared to FAT16, a FAT32 system
requires more storage space for the FATs because the entries are twice as
long.
Every FAT32 volume has these components:
• Reserved region, which contains the boot sector.
• FAT region, which contains two copies of the file allocation tables
(FATs).
• File and directory data region, which can hold the root directory, files,
and subdirectories.
These components are stored in sequence in the volume.
The sections that follow focus on the differences between FAT32 and
FAT16 and assume you're familiar with the preceding information about
FAT16.
Reserved Region
The first region in a FAT32 volume is the reserved region, which consists of
the boot sector, an FSInfo structure containing information to help in find-
ing free clusters, and a backup copy of the boot sector.
The Boot Sector
As with FAT16, the boot sector begins at the LBA value stored in the vol-
ume's entry in the partition table. Table 3-4 shows the first 90 bytes in a
FAT32 boot sector. Technically, the BIOS parameter block (BPB) consists of
the data in bytes 11-63, while the remaining bytes are part of the boot sec-
tor but not in the BPB.
Compared to FAT16, a FAT32 BPB has these differences:
•
The number of reserved sectors in byte 14 is typically 32 rather than 1.
•
The maximum number of entries in the root directory in byte 17 is
unused because FAT32 has no limit.
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