APPENDIX E : LOGICAL AND PHYSICAL RECORD FORMATS

       E.1  PHYSICAL RECORD STRUCTURE

            Each  physical  record  has  a  physical  record   header
       followed by data from logical records.  The format is:-

       Word (32 Bits)     Definition

         0         Length of Physical Record (LPR)
         1         Length of Physical Record Header (LPH)
         2         Physical Record Number (NPR)
         3         Displacement to first logical record (LRD)
         4 (LPH)   )
         ...       ) Data from previous logical record (if any)
         LRD-1     )
         LRD       Start of first logical record
         ...       Data
         LPR       Last dataword


            1.  All entries in the Physical Record Header are 32  Bit
                quantities    and    displacements    are    32   Bit
                displacements.

            2.  The Length of Physical Record contains  an  exclusive
                count  of the number of 32 Bit words following in the
                physical record (i.e.  not including itself).

            3.  The Length of Physical Record Header is an  inclusive
                count  of  the number of 32 Bit words in the Physical
                Record  Header  and  is  set  to  4  in  the  current
                implementation.   It  may be used as the displacement
                to the first dataword (either from a previous logical
                record,  or  the  wordcount for a logical record that
                immediately follows  this  Header)  in  the  physical
                record.

            4.  The Physical Record Number identifies  each  physical
                record on tape, beginning from 0.

            5.  Displacement to first word of logical  record  points
                to  the  first  word (wordcount) of the first logical
                record commencing in this physical record relative to
                word  0.   Thus  in  the  case where a logical record
                immediately follows this Physical Record  Header  the
                Displacement is set to 4.


       E.2  LOGICAL RECORD STRUCTURE

            The Logical Record Structure is as follows:-

               Length of Logical Record            One 32 Bit word
               Bank "LRID"             Variable No. of 32 Bit words
               .......
               .......
               Bank "ZZZZ"             Variable No. of 32 Bit words


            The Length of the Logical Record is an exclusive count of
       the  number of 32 Bit words in the Record (i.e.  not including
       itself).  Apart from  this  Length  word  the  Logical  Record
       consists  solely  of  YBOS  Banks.   Note  that  there are two
       special cases:-

            Length = 0

            This signifies that the length of the logical record  was
       not  known  at  creation time and must therefore be calculated
       from the information contained in the physical record headers.

            Length = -1

            This signifies a "null" logical record and that the  next
       true  logical  record  commences  at the beginning of the next
       physical record (after the physical record header).