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Guy Harris (talk | contribs) →Sequential organization: "type of data set organization used by VSAM", as for other types, not a "type of VSAM". |
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===Sequential organization===
An '''entry-sequenced data set''' ('''ESDS''') 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 sequential order, that is, the order in which they were written to the file;<ref>{{cite web|url=https://walton.uark.edu/enterprise/IBM/systemZ/downloads/module3/VSAM-Introductory.ppt|title=VSAM: introductory}}</ref><ref>{{cite web |title=Server Functionality |url=https://supportline.microfocus.com/documentation/books/tps62/mafunc.htm |quote=Sequential (VSAM ESDS – Entry Sequenced Dataset)}}</ref><ref>{{cite web|url=http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.469.8853&rep=rep1&type=pdf|quote=An ESDS VSAM data set contains records in the order in which they were entered|title=ABCs of z/OS System Programming Volume 3|citeseerx=10.1.1.469.8853}}</ref> which means that accessing a particular record involves searching all the records [[Sequential access|sequentially]] until it is located, or by using a relative physical address (''Relative byte address'', RBA), i.e. the number of bytes from the beginning of the file to start reading.<ref name="demystified"/>{{rp|28}}
Records are loaded irrespective of their contents and their byte addresses cannot be changed.
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