Content deleted Content added
→Overview: (section) - VSAM Primer |
→Overview: Control Intervals - 2 citations |
||
Line 9:
|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>{{cite web
|url=https://www.tutorialZpoint.com/vsam/vsam_components.htm |title=VSAM - Components}}</ref><ref>{{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. 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).
Both [[IMS/DB]] and [[IBM DB2|DB2]] are implemented on top of VSAM and use its underlying [[data structure]]s.<ref>{{cite web
| |||