NT 4.0 contains file system tunneling capabilities to allow for compatibility with applications that rely on file systems being able to hold onto file meta-info for a short period of time. This occurs after deletion or renaming and re-introducing a new directory entry with that meta-info (if a create or rename occurs to cause a file of that name to appear again in a short period of time). The idea is to mimic the behavior DOS applications expect when they use the safe save method. They copy the modified data to a temporary file, delete the original and rename the temporary to the original. This should appear to be the original file when complete. Windows NT performs tunneling on both FAT and NTFS file systems to ensure long/short file names are retained when 16-bit applications perform this safe save operation. See Q172190