FAT Folder Structure

Folders have set of 32-byte Folder Entries for each file and subfolder contained in the folder (see example figure below).

The Folder Entry includes the following information:

  • Name (eight-plus-three characters)
  • Attribute byte (8 bits worth of information, described later in this section)
  • Create time (24 bits)
  • Create date (16 bits)
  • Last access date (16 bits)
  • Last modified time (16 bits)
  • Last modified date (16 bits)
  • Starting cluster number in the file allocation table (16 bits)
  • File size (32 bits)

There is no organization to the FAT folder structure, and files are given the first available location on the volume. The starting cluster number is the address of the first cluster used by the file. Each cluster contains a pointer to the next cluster in the file, or an indication (0xFFFF) that this cluster is the end of the file. See File Allocation System for details.

The information in the folder is used by all operating systems that support the FAT file system. In addition, Windows NT can store additional time stamps in a FAT folder entry. These time stamps show when the file was created or last accessed and are used principally by POSIX applications.

Because all entries in a folder are the same size, the attribute byte for each entry in a folder describes what kind of entry it is. One bit indicates that the entry is for a subfolder, while another bit marks the entry as a volume label. Normally, only the operating system controls the settings of these bits.

A FAT file has four attributes bits that can be turned on or off by the user - archive file, system file, hidden file, and read-only file.

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