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.

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, se 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