5.6 VSAM Differences

5.6.1 Introduction

This section covers the differences between OS/390 VSAM and VSE/VSAM. In OS/390, the functions of VSAM and other OS/390 access methods are provided by the OS/390 Data Facility Product (DFP). The term ICF refers to the Integrated Catalog Facility. The term AMS refers to Access Method Services and/or the program IDCAMS. All data set references are to VSAM data sets.

A complete set of DFSMS/MVS publications can be found in the DFSMS/MVS Library Guide, GC26-4902 and DFSMS/MVS General Information, GC26-4900.

Planning information for Data Facility Systems Managed Storage (DFSMS) can be found in the following manuals:

DFSMS/MVS General Information, GC26-4900

DFSMS/MVS Planning for Installation, SC26-4919

Implementing System-Managed Storage, SC26-3123

Get DFSMS FIT: Fast Implementation Techniques, SG24-2568

DFSMS FIT: Fast Implementation Techniques Process Guide, SG24-4478

DFSMS FIT: Fast Implementation Techniques Installation Examples, SG24-2569

RACF General Information, GC23-3723

Getting Started with DFSORT, SC26-4109

5.6.2 OS/390 Catalogs

At the time of writing, there are three catalog types supported in OS/390. After the end of 1999, only ICF catalogs will be supported in the OS/390 environment. The current catalog types are:

ICF catalogs - are the recommended catalog structures for your OS/390 system.

VSAM catalogs - these are similar and mostly compatible5 to VSE/VSAM catalogs. They do not provide the performance and recoverability of ICF catalogs. They are not recommended for normal OS/390 production operations. However, they do provide catalog portability between VSE and OS/390. If used, they should be converted to ICF catalogs when the migration is completed. Details on converting to ICF catalogs can be found in Managing Catalogs, SC26-4914, chapter 9.

The VSAM catalog stores dates with two-digit years. VSE/VSAM has implemented a sliding window interpretation of those dates. OS/390 (DFP) has not made similar changes, and thus dates in VSAM catalogs will not be correctly interpreted in OS/390 systems. Because of this, OS/390 (DFP) has announced that VSAM catalogs will not be supported after December 31st 1999.

5Compatibility between VSE/VSAM catalogs and OS/390 VSAM catalogs is discussed in the section entitled 5.6.4, ªOS/390 - VSE/VSAM Catalog Compatibilityº on page 117.

110VSE to OS/390 Migration Workbook

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IBM manual Vsam Differences Introduction, 2 OS/390 Catalogs

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.