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BPAM provides an [[application program interface]] (API) to allow programmers to access libraries directly. The BPAM API is similar to [[basic sequential access method]] (BSAM), but it adds functionality to process directories. Individual members of a PDS can also be processed using sequential access methods by specifying the member name on the job control ''DD'' statement.
The programmer specifies <code>DSORG=PO</code> in their [[Data Control Block]] (DCB) to indicate use of BPAM.
As a ''basic'' access method BPAM reads and writes member data in [[Block (data storage)|blocks]] and the I/O operation proceeds [[Asynchronous I/O|asynchronously]] and must be tested for completion using the <code>CHECK</code> macro.<ref name=Macro>{{cite book|last1=IBM Corporation|title=OS Data Management Macro Instructions|date=June 1973|page=157|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/os/R21.7_Apr73/GC26-3794-1_OS_Data_Management_Macro_Instructions_Rel_21.7_Jun73.pdf|accessdate=August 19, 2016}}</ref> BPAM uses the standard system macros <code>OPEN</code>, <code>CLOSE</code>, <code>READ</code>, <code>WRITE</code>,and <code>CHECK</code>. The <code>NOTE</code> macro instruction returns position of the last block read or written, and the <code>POINT</code> macro will reposition to the ___location identified by a previous <code>NOTE</code>.<ref name=Macro /> The <code>BLDL</code> macro can be used to build a list of the addresses of members specified by the programmer for later use, if desired. <code>FIND</code> positions to a single member, specified by name, which requires a directory lookup on disk, or by address previously retrieved by <code>BLDL</code>. The <code>STOW</code> macro is used to update the directory when a member is added, deleted, changed (including renamed), or replaced.<ref>{{cite book|last1=IBM Corporation|title=OS Data Management Services Guide|date=July 1973|pages=75–85|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/360/os/R21.7_Apr73/GC26-3746-2_OS_Data_Management_Services_Guide_Rel_21.7_Jul73.pdf|accessdate=August 19, 2016}}</ref>
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