for breakdown of CMD format, see www.tim-mann.org/trs80/doc/ldosq1-4.txt ( Roy‘s Technical Corner P42)

 files consist of unordered records.
 reach record consists of a one byte record type, followed by a 2 byte record length field, followed by a data area (who's length is specified by the 'record length' field

         TYPE     DATA AREA
          ----     ---------
           01      object code (load block)
           02      transfer address
           04      end of partitioned data set member
           05      load module header
           06      partitioned data set header
           07      patch name header
           08      ISAM directory entry
           0A      end of ISAM directory
           0C      PDS directory entry
           0E      end of PDS directory
           10      yanked load block
           1F      copyright block