Enterprise COBOL for z/OS, Version 4.2, Programming Guide
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 table below shows how VSAM terms differ from COBOL terms and other terms that you might be familiar with.
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, review the VSAM publications for your operating system.
Related concepts
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