Filenames on FAT Volumes

Beginning with Windows NT 3.5, files created or renamed on FAT volumes use the attribute bits to support long filenames in a way that does not interfere with how MS-DOS or OS/2 accesses the volume.

Whenever a user creates a file with a long filename, Windows creates an eight-plus-three name for the file. In addition to this conventional entry, Windows creates one or more secondary folder entries for the file, one for each 13 characters in the long filename. Each of these secondary folder entries stores a corresponding part of the long filename in Unicode.

Windows sets the volume, read-only, system, and hidden file attribute bits of the secondary folder entry to mark it as part of a long filename.

MS-DOS and OS/2 generally ignore folder entries with all four of these attribute bits set, so these entries are effectively invisible to these operating systems. Instead, MS-DOS and OS/2 access the file by using the conventional eight-plus-three filename contained in the folder entry for the file.

Example of Folder Entries for the long filename

The Figure below shows all of the folder entries for the file, which has a long name of The quick The long name is in Unicode, so each character in the name uses two bytes in the folder entry. The attribute field for the long name entries has the value 0x0F. The attribute field for the short name is 0x20.

Long File Name Folder Entry Example

NTFS: Long File Name

Windows NT/2000/XP and Windows 95/98/ME use the same algorithm to create long and short filenames. On computers that dual-boot these two operating systems, files that you create when running one of the operating systems can be accessed when running the other.