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Line 51: ===Relative organization=== A '''relative record data set''' (RRDS) is a type of [[data set (IBM mainframe)\|data set]] organization used by VSAM.<ref name="demystified"/>{{rp\|5}} Records are accessed based on their ordinal position in the file (''relative record number'', RRN).<ref name="demystified"/>{{rp\|29}} For example, the desired record to be accessed might be the 42nd record in the file out of 999 total. The concept of RRDS is similar to [[sequential access]] method, but it can access with data in [[random access]] and dynamic access.{{huh\|date=April 2021}} ~~{{further\|relative record data set}}~~ An RRDS consists of data records in sequence, with the record number indicating the record's logical position in the data set.<ref name="demystified"/>{{rp\|29}} A program can access records randomly using this positional number or access records sequentially.<ref name="demystified"/>{{rp\|30}} But unlike a [[Key Sequenced Data Set]], an RRDS has no keys, so the program cannot access records by key value. ~~An RRDS may have an index defined to it to enable access via keys, by defining an Alternate Index.~~ === Linear organization === Line 79: ==History== VSAM was introduced as a replacement for older access methods<ref>{{cite manual\|title = OS/Virtual Storage 1 Features Supplement \|id = GC20-1752-0\| date = August 1972\|edition = First\|url = http://bitsavers.org/pdf/ibm/370/OS_VS1/GC20-1752-0_OS_VS1_Features_Supplement_Aug72.pdf\| publisher = IBM}} ~~\| title = OS/Virtual Storage 1 Features Supplement~~ ~~\| id = GC20-1752-0~~ ~~\| date = August 1972~~ ~~\| edition = First~~ ~~\| url = http://bitsavers.org/pdf/ibm/370/OS_VS1/GC20-1752-0_OS_VS1_Features_Supplement_Aug72.pdf~~ ~~\| publisher = IBM~~ }} </ref> and was intended to add function, to be easier to use and to overcome problems of performance and device-dependence. VSAM was introduced in the 1970s when IBM announced [[virtual memory\|virtual storage]] operating systems (DOS/VS, OS/VS1 and OS/VS2) for its new System/370 series, as successors of the [[DOS/360 and successors\|DOS/360]] and [[OS/360 and successors\|OS/360]] operating systems running on its System/360 computer series. While backwards compatibility was maintained, the older access methods suffered from performance problems due to the address translation required for virtual storage. Line 115 ⟶ 108: {{cite manual\|title = z/OS 2.5 MVS Programming: Assembler Services Guide\|id = SA23-1368-50\|date = September 30, 2021\|url = https://www.ibm.com/servers/resourcelink/svc00100.nsf/pages/zOSV2R5sa231368/$file/ieaa600_v2r5.pdf\|ref = {{sfnref\|ASMGUIDE}}\| publisher = IBM}} {{cite web\|url=http://www.mvsforums.com/techfaqsvsam.html\|title=MVS Forums - Technical FAQ's - VSAM\|website=Mvsforums.com\|accessdate=12 December 2017}} ==External links== [https://web.archive.org/web/20051023212932/http://www.lascon.co.uk/d002303.htm Lascon.co.uk] [https://web.archive.org/web/20070311021954/http://www.redbooks.ibm.com/redbooks/SG246105/wwhelp/wwhimpl/js/html/wwhelp.htm Redbooks.ibm.com] https://web.archive.org/web/20051013071230/http://www.jaymoseley.com/hercules/vstutor/vstutor.htm http://www.mvsforums.com/techfaqsvsam.html *https://web.archive.org/web/20070311021954/http://www.redbooks.ibm.com/redbooks/SG246105/wwhelp/wwhimpl/js/html/wwhelp.htm {{Mainframe I/O access methods}}

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