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VSAM stands for Virtual Storage Access Method. VSAM is a file storage access method used in MVS, ZOS and OS/390 operating systems. It was introduced by IBM in 1970’s. It is a high performance access method used to organize data in form of files in Mainframes. VSAM is used by COBOL and CICS in Mainframes to store and retrieve data. VSAM makes it easier for application programs to execute an input-output operation.

Audience

This tutorial is designed for software programmers with a need to understand the VSAM concepts starting from scratch. This tutorial will give you enough understanding on VSAM from where you can take yourself to higher level of expertise.

Prerequisites

Before proceeding with this tutorial, you should have a basic understanding of JCL and COBOL. A basic understanding of any of the file handling method will help you in understanding the VSAM concepts and move fast on the learning track.

Overview

Virtual Storage Access Method (VSAM) is high performance access method and data set organization, which organizes and maintains data via a catalog structure. It utilizes virtual storage concept and can protect datasets at various levels by giving passwords. VSAM can be used in COBOL programs like physical sequential files. VSAM are the logical datasets for storing records. Files can be read sequentially and randomly in VSAM. It is an improved way of storing data which overcomes some of the limitations of conventional file systems like Sequential Files.

Characteristics of VSAM

Following are the characteristics of VSAM −

  • VSAM protects data against unauthorized access by using passwords.
  • VSAM provides fast access to data sets.
  • VSAM has options for optimizing performance.
  • VSAM allows data set sharing in both batch and online environment.
  • VSAM are more structured and organized in storing data.
  • Free space is reused automatically in VSAM files.

Limitations of VSAM

The only limitation of VSAM is that it cannot be stored on TAPE volume. It is always stored on DASD space. It requires a number of cylinders to store the data which is not cost-effective.

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