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.