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  Function 68H (decimal 104) was first supported in DOS version 3.3. When
  you call this function with an open file handle in BX, DOS flushes the
  disk buffer associated with the handle and updates the disk directory
  accordingly. This ensures that data written to the disk buffer but not yet
  physically written on a disk will not be lost should a power failure or
  other mishap occur.

  By executing function 68H, you obtain the same result that you would by
  using function 45H to duplicate a file handle and then using function
  3EH to close the duplicate handle.