The job entry subsystem (JES) spools and schedules input and output data streams. It controls all blocking and deblocking of your data to make the best use of system operation. The BSAM NCP value has an effect on the access method, but a value greater than 1 does not improve performance. NCP is supported for compatibility with other data sets. The block size (BLKSIZE) and number of buffers (BUFNO) specified in your program have no relationship with what is actually used by the job entry subsystem. Therefore, you can select the blocking factor that best fits your application program with no effect on the spooling efficiency of the system. For QSAM applications, move mode is as efficient as locate mode.

SYSIN and SYSOUT data sets cannot be system managed. SYSIN and SYSOUT must be either BSAM or QSAM data sets and you open and close them in the same manner as any other data set processed on a unit record device. Because SYSIN and SYSOUT data sets are spooled on intermediate devices, you should avoid using device-dependent macros (such as FEOV, CNTRL, PRTOV, or BSP) in processing these data sets. See Achieving Device Independence. You can use PRTOV, but it will have no effect. For more information about SYSIN and SYSOUT parameters see z/OS MVS JCL User's Guide and z/OS MVS JCL Reference. Your SYNAD routine is entered if an error occurs during data transmission to or from an intermediate storage device. Again, because the specific device is indeterminate, your SYNAD routine code should be device independent. If you specify the DCB open exit routine in an exit list, it will be entered in the usual manner. See DCB Exit List for the DCB exit list format and DCB OPEN Exit.