There are several common blocks which are essential to the running of the program and can only be changed by editing and recompiling spi.pgm and reinitializing the S file with these new values. This should only be done with extreme caution since incorrect or faulty modifications can corrupt the S file and cause the loss of all stored data!! The values in STORAGE.INC are explicitly set in the program whereas all remaining control block values are defined in the block data section at the end of the program.
One reason to modify the function blocks is to increase the size of the S file. The capacity of the S file is controlled the variable MAXSREC located in the common block STORAGE. This value is explicitly set on line 406 of spi.pgm and is set to 4000. Since each block is LENSREC 1024 bytes in length, the size capacity of the S file is MAXSREC LENSREC 1024 bytes. These values are set to MAXSREC=4000 and LENSREC=5.