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XDAP must reference an OPENed DCB and a full direct access record identifier. The DCB may be OPENed for input, for output or for input and output, but all outputs must be update writes of existing records as XDAP does not support format writes. BSAM and BPAM are available for executing format writes (writes which add new records to the dataset).
The IOBSPSVC flag (logically, the '''IOB''''s '''S'''AM and '''P'''AM '''SVC''' flag) is available, and which causes SAM and PAM appendages to be bypassed. This enhancement, which was first implemented with SVS, but was not retrofitted to previous versions of the OS, significantly facilitated processing a dataset OPENed for BSAM or BPAM, while using XDAP. Otherwise, certain SAM and PAM appendages could cause random supervisor storage overlays when presented with certain XDAP channel programs. An obvious circumvention, mainly for pre-SVS systems, was to utilize only those XDAP channel programs which did not also utilize RPS, as IBM did not guarantee system security and data integrity on pre-MVS instances of the OS.
[[Category:IBM Mainframe computer operating systems]]
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