Processing VSAM files

Virtual storage access method (VSAM) is an access method for files on direct-access storage devices. With VSAM you can load files, retrieve records from files, update files, and add, replace, and delete records in files.

About this task

VSAM processing has these advantages over QSAM:

Protection of data against unauthorized access
Compatibility across systems
Independence of devices (no need to be concerned with block size and other control information)
Simpler JCL (information needed by the system is provided in integrated catalogs)
Ability to use indexed file organization or relative file organization

The following table shows how VSAM terms differ from COBOL terms and other terms that you might be familiar with.

Table 1. **Comparison of VSAM, COBOL, and non-VSAM terminology**
VSAM term	COBOL term	Similar non-VSAM term
Data set	File	Data set
Entry-sequenced data set (ESDS)	Sequential file	QSAM data set
Key-sequenced data set (KSDS)	Indexed file	ISAM data set
Relative-record data set (RRDS)	Relative file	BDAM data set
Control interval		Block
Control interval size (CISZ)		Block size
Buffers (BUFNI/BUFND)		BUFNO
Access method control block (ACB)		Data control block (DCB)
Cluster (CL)		Data set
Cluster definition		Data-set allocation
`AMP` parameter of JCL `DD` statement		`DCB` parameter of JCL `DD` statement
Record size		Record length

The term file in this VSAM documentation refers to either a COBOL file or a VSAM data set.

If you have complex requirements or frequently use VSAM, see the VSAM publications for your operating system.

Related concepts
VSAM files

Related references
z/OS DFSMS: Using Data Sets
z/OS DFSMS Macro Instructions for Data Sets
z/OS DFSMS: Access Method Services for Catalogs
Allocation of record areas for VSAM files
Extended addressability support