• If a file opened with the INPUT phrase is an optional file which is not present, the OPEN statement sets the file position indicator to indicate that an optional input file is not present.

• Execution of an OPEN INPUT or OPEN I-O statement sets the file position indicator:
  • For indexed files, to the characters with the lowest ordinal position in the collating sequence associated with the file.

  • For sequential and relative files, to 1.

• When the EXTEND phrase is specified, the OPEN statement positions the file immediately after the last record written in the file. (The record with the highest prime record key value (for indexed files) or relative key value (for relative files) is considered the last record.) Subsequent WRITE statements add records as if the file were opened OUTPUT. The EXTEND option can be specified when a file is being created; it can also be specified for a file that contains records, or that has contained records that have been deleted.

• X >_OS/2_> Any OS/2 VSAM files, that specify the LOCK MODE IS AUTOMATIC
  X phrase are shareable (except for any VSAM files residing on a LAN
  X server). Shareable files can be opened by more than one file
  X connector. If the OPEN statement fails due to locking constraints,
  X the file status is set to indicate "file locked." <_OS/2_<

• >_Workstation_> When the EXTEND phrase is not specified, OPEN statement positions the file at its beginning. <_Workstation_<

• >_Host_> For OS/390 VSAM files, if no records exist in the file, the file position indicator is set so that the first Format 1 READ statement executed results in an AT END condition.

• When NO REWIND is specified, the OPEN statement execution does not reposition the file; prior to OPEN statement execution, the file must be positioned at its beginning. When the NO REWIND phrase is specified (or when both the NO REWIND and REVERSE phrases are omitted), file positioning is specified with the LABEL parameter of the DD statement under OS/390 and with the "label processing" operand under CMS.

• When REVERSED is specified, OPEN statement execution positions the QSAM file at its end. Subsequent READ statements make the data records available in reversed order, starting with the last record.
  When OPEN REVERSED is specified, the record format must be fixed.

• When the REVERSED, NO REWIND, or EXTEND phrases are not specified, OPEN statement execution positions the file at its beginning. <_Host_<

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