CMS file system: Difference between revisions

Revision as of 13:28, 8 August 2016

Revision as of 00:22, 17 January 2017

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==Disk organization==

CMS uses [[virtual disk]]s called ''minidisks'' to store files. A minidisk is a contiguous subset of a real disk which functions like a real disk. VM allows minidiaksminidisks to contain various types of data such as [[OS/360]] or [[DOS/360]] datasets as well as CMS-formatted data.

A CMS virtual machine can have up to ten minidisks accessed during one session. The user references the minidisks by a letter, part of a field called the ''filemode''. The ''S'' disk contains CMS system files and is read-only. The ''A'' disk contains user files such as customization data, program sources, and executables. Other drive letters ''B'' through ''Z'' can contain data as defined by the user. If a file is opened without a filemode letter specified (<code> FILENAME FILETYPE *</code>) the disks will be searched in alphabetic order. The second character of the filemode is a number indicating read, write, and sharing attributes.<ref name="IBMKB">{{cite web|last1=IBM Corporation|title=File Mode Letters and Numbers|url=https://www.ibm.com/support/knowledgecenter/SSB27U_6.2.0/com.ibm.zvm.v620.dmsb3/letnums.htm|website=IBM Knowledge Center|accessdate=August 3, 2016}}</ref>