Processing VSAM Data Sets

There are two types of VSAM macro instructions:

Control block macros. Generate control blocks of information that VSAM needs to process the data set.
Request macros. Retrieve, update, delete, or insert logical records.

VSAM has two major parts:

Catalog management. VSAM maintains extensive information about data sets and direct access storage space in a catalog. The catalog's collection of information about a particular data set defines that data set's characteristics. Every VSAM data set must be defined in a catalog. You cannot, for example, load records into a VSAM data set until it has been defined. See z/OS DFSMS Managing Catalogs for information about catalog management.
Record management. You can use VSAM to organize records into four types of data sets: key-sequenced, entry-sequenced, linear, or relative record. The primary difference among these types of data sets is the way their records are stored and accessed.

Restriction: VSAM data sets cannot be concatenated in JCL statements.