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|title=VSAM - Components}}</ref><ref name=VSAM.CI2>{{cite web
|url=https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.1.0/com.ibm.zos.v2r1.idad400/d4221.htm
|title=Control Interval Size Limitations|website=[[IBM]] |date=27 March 2014 }}</ref> and then into larger divisions called Control Areas (CAs). Control Interval sizes are measured in bytes{{snd}} for example 4 [[kilobyte]]s{{snd}} while Control Area sizes are measured in disk tracks or cylinders. Control Intervals are the units of transfer between disk and computer so a read request will read one complete Control Interval. Control Areas are the units of allocation so, when a VSAM data set is defined, an integral number of Control Areas will be allocated.
The Access Method Services utility program [[IBM mainframe utility programs#IDCAMS|IDCAMS]] is commonly used to manipulate ("delete and define") VSAM data sets. Custom programs can access VSAM datasets through Data Definition (DD) statements in [[Job Control Language]] (JCL), via dynamic allocation or in online regions such as in [[CICS|Customer Information Control System]] (CICS).
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|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> Records are loaded irrespective of their contents and their byte addresses cannot be changed. ===Indexed VSAM organization===
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* Local Shared Resources (LSR), is optimised for "random" or direct access. LSR access is easy to achieve from [[CICS]].<ref name=VSAM.LSRorNSR>{{cite web
|url=https://www.ibm.com/support/knowledgecenter/SSGMCP_5.6.0/tuning/dfht3c00200.html
|title=Local shared resources (LSR) or nonshared resources|website=[[IBM]] }}</ref>
* Global Shared Resources (GSR)<ref name=VSAM.GSR>{{cite web |website=IBM.com (IBM Knowledge Center)
|url=https://www.ibm.com/support/knowledgecenter/SSLTBW_2.3.0/com.ibm.zos.v2r3.idad400/share.htm
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