Directories - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 205

creation date and time should remain unchanged. If unused, these fields
should contain zeros.
The file-last-accessed date (bytes 18 - 19) stores the date when the file was
last accessed. Many applications don't update this value or do so in inconsis-
tent ways, so the stored information is of little use. If unused, these fields
should contain zeros.
The FAT32 specification says that the file-modified date and time are
required. The other dates and times are optional. An embedded system
should support the file-modified fields if possible.
First Cluster
The first-cluster entry at offset 26 is the number of the file's first data cluster
(FAT16) or the low word of the file's first data cluster (FAT32). For FAT32
volumes, offset 20 contains the high word of the file's first data cluster. The
first data cluster in the data area is cluster 2, so the first-cluster number must
be 2 or greater.
File Size
The file size field at offset 28 stores the size of the file in bytes.
Directory Entries
A directory entry is the same as a file entry with these exceptions:
Bit 1 in the Attributes field is set to 1 to indicate that the entry is for a
directory.
The file-size field is zero.
In a FAT16 partition, the root directory follows the FATs. In a FAT32 parti-
tion, the root directory typically begins in cluster 2 in the data area. Offset
44 in a FAT32 volume's boot sector contains the cluster number where the
root directory begins.
The first two entries in a subdirectory are the dot and dotdot entries:
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