Introduction to VSAM programming

You use the virtual storage access method (VSAM) to organize data and maintain information about that data in a catalog. Perform VSAM programming using access method services commands and VSAM macros.

Access method services. You define VSAM data sets and establish catalogs using a multi-function services program called access method services.
Job control language. You can define VSAM data sets using JCL.
Dynamic Allocation. You can define or allocate to data sets using dynamic allocation, which is SVC 99. Dynamic allocation is described in z/OS MVS Programming: Authorized Assembler Services Guide. VSAM supports the nocapture option of dynamic allocation. It reduces overhead of dynamic allocation and reduces virtual storage usage below the 16 MB line.
VSAM macro instructions. Two types of VSAM macros are used to process VSAM data sets:
- Control block macros generate control blocks of information needed by VSAM to process the data set.
- Request macros are used to retrieve, update, delete, or insert logical records.

All macros described in this book are in the main system macro library, SYS1.MACLIB.

You can use 24-bit or 31-bit addressing mode for VSAM programs. If you use 31-bit support, see z/OS DFSMS Using Data Sets for procedures and restrictions.