You can use the BSP macro to backspace the current member one simulated block. You can then reread or rewrite the simulated block. However, you cannot backspace beyond the start of a PDSE member nor backspace within the PDSE directory.

For variable spanned records (RECFM=VS), if positioned to the beginning of a record, the BSP macro backspaces to the start of the previous record. If positioned within a record, the BSP macro backspaces to the start of that record.

For variable blocked spanned (RECFM=VBS) records, the BSP macro backspaces to the start of the first record in the buffer just read. The system does not backspace within record segments. Issuing the BSP macro followed by a read always begins the block with the first record segment or complete segment. (A block can contain more than one record segment.)

If you write in a PDSE member and issue the BSP macro followed by a WRITE macro, you destroy all the data of the member beyond the record just written.