CMS file system: Difference between revisions

Revision as of 09:37, 1 March 2019

Revision as of 08:40, 2 March 2019

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Records are usually called ''items'' in CMS terminology. CMS files can have either ''fixed'' or ''variable'' record format; record types may not be mixed in a file. For fixed-length records the length is defined by FSTLRECL, and the ___location of any fixed-length record can be computed by (item_number-1) * record_length/800. The quotient will be the block number and the remainder will be the offset of the item in the block. Variable-length records have a maximum length of FSTLRECL bytes, and are preceded by a two-byte record length field indicating the actual length.

An enhancement to the original CMS file system in [[z/VM/SP]], called ''Enhanced Disk Format'' (EDF), allows larger files by expanding the FST and introducing multiple levels of chain link blocks.<ref>{{cite web|title=The CMS EDF file system|url=http://dforeman.cs.binghamton.edu/~foreman./550pages/VM/CMS-File-System-1.doc|website=binghamton.edu|accessdate=August 5, 2016}}</ref><ref>{{cite web|last1=IBM Corporation|title=FSTD|url=http://www.vm.ibm.com/pubs/cms530/FSTD.HTML|website=ibm.com|accessdate=August 5, 2016}}</ref>

==References==