Long Filename - Compatibility Issues

Compatibility Issues

Microsoft implemented support for LFNs in the FAT filesystem by using hidden directory entries—of the volume label type—to store the longer names. This so-called VFAT scheme was chosen for compatibility; volume labels are generally ignored by programs and operating system components. Programs running on older operating systems could still access the files' short names, while newer, LFN-aware operating systems and programs could use the longer ones.

When LFNs were first introduced into an MS-DOS-based operating system with Windows 95, they caused some problems for older programs. For example, a DOS program performing sector-level directory operations while Windows was in DOS mode could destroy long filename information so, by default, sector-level access to hard disks was disallowed in this mode.

Upon booting into plain DOS the long filenames would not be visible unless a VFAT LFN driver had been installed (see below). Microsoft did not add LFN support to many of its older programs, including File Manager, the Windows for Workgroups file manager that was made obsolete by the new operating system shell, Explorer). Windows NT supported LFNs on NTFS file systems beginning with the release of NT 3.1, and all of its utilities, including File Manager, were updated to support LFNs. NT 3.5 added FAT LFN support in preparation for Windows 95. However, the Windows 95 version of File Manager came from Windows for Workgroups 3.11.

OS/2 stored LFNs for FAT filesystems in .LONGNAME extended attributes that were incompatible with Microsoft's implementation and only visible to tools supporting the new standard. Many APIs providing access to files by pathname could not see the new, longer names, although this shortcoming could be rectified by installing a driver.