Full_Description

   By default, when records are sorted with identical keys, the
   order of those records in the output file may not be the same as
   they appeared in the input file. Specifying the /STABLE qualifier
   in a specification file arranges records with equal keys in the
   output file in the order of the input files as specified in the
   command line. If you use this qualifier when sorting multiple
   input files, on output, records with equal keys in the first file
   will precede those from the second file and so on.