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Basic sequential access method
open-in-new
<h2 id="application-program-interface">Application program interface</h2> <p>The programmer specifies DSORG=PS in his <a href="/facts/Data_Control_Block/7h7UQ9R9">Data Control Block</a> (DCB) to indicate use of BSAM. As a <i>basic</i> access method BSAM reads and writes member data in <a href="/facts/Block_(data_storage)/S3vT7c6N">blocks</a> and the I/O operation proceeds <a href="/facts/Asynchronous_I%2fO/6A7V3P89">asynchronously</a> and must be tested for completion using the CHECK macro.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> BSAM uses the standard system macros OPEN, CLOSE, READ, WRITE,and CHECK. The NOTE macro instruction returns position of the last block read or written, and the POINT macro will reposition to the location identified by a previous NOTE.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p><p>If the dataset is unblocked, that is, the logical record length (LRECL) is equal to the physical block size (BLKSIZE), BSAM may be utilized to simulate a directly accessed dataset using NOTE and POINT on any supported direct access device type (DEVD=DA), and some primitive applications were designed in this way. </p> <h2 id="similar-facilities">Similar facilities</h2> <p>The BSAM application program interface can be compared with the interface offered by <i>open</i>, <i>read</i>, <i>write</i> and <i>close</i> calls (using file handles) in other operating systems such as <a href="/facts/Unix/0pNL2seI">Unix</a> and <a href="/facts/Microsoft_Windows/bwhAhuSL">Windows</a>. POINT provides an analog of <i>seek</i> or <i>lseek</i>,and <i>ftell</i> is the equivalent of NOTE. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Queued_Sequential_Access_Method/naEYsP3B">Queued Sequential Access Method</a> (QSAM)</li> <li><a href="/facts/Hierarchical_Sequential_Access_Method/bW0zbK9N">Hierarchical Sequential Access Method</a> (HSAM)</li> <li><a href="/facts/Basic_Indexed_Sequential_Access_Method/J1Q7sty3">Basic Indexed Sequential Access Method</a> (BISAM)</li> <li><a href="/facts/Queued_Indexed_Sequential_Access_Method/J1Q7sty3">Queued Indexed Sequential Access Method</a> (QISAM)</li> <li><a href="/facts/Hierarchical_Indexed_Sequential_Access_Method/J1Q7sty3">Hierarchical Indexed Sequential Access Method</a> (HISAM)</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>IBM System/360 Operating System Sequential Access Methods Program Logic Manual (PDF). IBM. January 1967. Y28-6604-1. <a href="http://www.bitsavers.org/pdf/ibm/360/os/plm_1966-67/Y28-6604-1_Sequential_Access_Methods_PLM_Jan67.pdf" target="_blank">http://www.bitsavers.org/pdf/ibm/360/os/plm_1966-67/Y28-6604-1_Sequential_Access_Methods_PLM_Jan67.pdf</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>IBM Corporation (June 1973). OS Data Management Macro Instructions (PDF). Retrieved August 19, 2016. <a href="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" target="_blank">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</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>IBM Corporation (June 1973). OS Data Management Macro Instructions (PDF). Retrieved August 19, 2016. <a href="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" target="_blank">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</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> </ol>