You can process a data set as input, output, or update by coding the processing method in the OPEN macro. If the processing method parameter is omitted from the OPEN macro, INPUT is assumed.

  INPUT—BDAM, BPAM, BSAM, QSAM
  OUTPUT—BDAM, BPAM, BSAM, QSAM
  EXTEND—BDAM, BPAM (PDSE only), BSAM, QSAM
  UPDAT—BDAM, BPAM, BSAM, QSAM
  RDBACK—BSAM, QSAM
  INOUT—BSAM
  OUTIN—BSAM
  OUTINX—BSAM

If the data set resides on a direct access volume, you can code UPDAT in the processing method parameter to show that records can be updated.

RDBACK is supported only for magnetic tape. By coding RDBACK, you can specify that a magnetic tape volume containing format-F or format-U records is to be read backward. (Variable-length records cannot be read backward.)

Restriction: When a tape that is recorded in Improved Data Recording Capability (IDRC) mode, is read backward, it will have a severe performance degradation.

You can override the INOUT, OUTIN, UPDAT, or OUTINX at execution time by using the IN or OUT options of the LABEL parameter of the DD statement, as discussed in z/OS MVS JCL Reference. The IN option indicates that a BSAM data set opened for INOUT or a direct data set opened for UPDAT is to be read only. The OUT option indicates that a BSAM data set opened for OUTIN or OUTINX is to be written in only.

Restriction: Unless allowed by the label validation installation exit, OPEN for OUTPUT or OUTIN with DISP=MOD, INOUT, EXTEND, or OUTINX requests cannot be processed for ISO/ANSI Version 3 tapes or for non-IBM-formatted Version 4 tapes, because this kind of processing updates only the closing label of the file, causing a label symmetry conflict. An unmatching label should not frame the other end of the file. This restriction does not apply to IBM-formatted ISO/ANSI Version 4 tapes.

Related reading: For information about the label validation installation exit, see z/OS DFSMS Installation Exits.

Processing SYSIN, SYSOUT, and subsystem data sets. INOUT is treated as INPUT. OUTIN, EXTEND, or OUTINX is treated as OUTPUT. UPDAT and RDBACK cannot be used. SYSIN and SYSOUT data sets must be opened for INPUT and OUTPUT, respectively.

Processing PDSEs. For PDSEs, INOUT is treated as INPUT. OUTIN, EXTEND, and OUTINX are treated as OUTPUT.

Processing compressed-format data sets. Compressed-format data sets must not be opened for UPDAT.

   OPEN      (TEXTDCB,,CONVDCB,(OUTPUT),PRINTDCB,                      X
             (OUTPUT))

Because no processing method parameter is specified for TEXTDCB, the system assumes INPUT. Both CONVDCB and PRINTDCB are opened for output. No volume positioning options are specified; thus, the disposition indicated by the DD statement DISP parameter is used.