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  Like the standard DOS RENAME command, function 56H (decimal 86) changes
  the name of a file. But it can also move a file's directory entry from one
  directory to another. The file itself is not moved, only the directory
  entry, which means the new and old directory paths must be on the same
  drive. This is a truly fabulous and useful feature, and it is rather
  disappointing that it's not a part of the RENAME command.

  This function needs two pieces of information: the old and new path and
  filenames. These can be full-blown file specifications, with drive and
  path components. The specified or implied drives must be the same so that
  the new directory entry will be on the same drive as the file. The
  wildcard characters * and ? cannot be used, because this function works on
  single files only.

  As usual, both file specifications are supplied in the form of ASCIIZ
  strings. The register pair DS:DX points to the old name string and ES:DI
  points to the new string.

  Function 56H clears the carry flag when it successfully renames a file. If
  an error occurs, the carry flag is set, and AX contains an error code: 02H
  (file not found), 03H (path not found), 05H (access denied), or 11H (not
  the same device). One error that might not be reported occurs if you use
  function 56H to rename an open file. Be sure to close an open file with
  function 10H or 3EH before you use function 56H to rename it.