Joined: 23 Nov 2006 Posts: 19270 Location: Inside the Matrix
Please post in a correct forum. Your post has nothing to do with COBOL. . .
There is not so much a difference between "each two" as they are completely un-related.
A PS is sequential file - a single set of records, typically processed from first to last.
A PDS is a partioned dataset - it may contain multiple sets of records called members.
The Catalog is the place where dataset location information is stored. For each "catalog"ed dataset, there is an entry in the catalog. This is typically how the system locates a dataset when it is referenced by some process.