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|title=VSAM Primer}}</ref> IBM uses the term ''data set'' in official documentation as a synonym of ''file'', and ''[[direct access storage device]]'' (''DASD'') because it supported other devices similar to ''disk drives''.
VSAM records can be of fixed or variable length. They are organised in fixed-size blocks called [[Control Interval]]s (CIs),<ref name=VSAM.CI1>{{cite web
|url=https://www.tutorialZpoint.com/vsam/vsam_components.htm
|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}}</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.
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