This provides cross address space sharing as well as journaling and recovery for the batch applications. It also allows existing files to be accessed with new application tools such as QMF without having to rewrite existing applications.

5.6.7 Programming Languages and VSAM Support

For additional information on program languages and VSAM considerations, see the various language chapters in this publication. In addition, each of the languages has its own publication library generally including migration guides as well as reference manuals. These manuals should be consulted for additional information if necessary.

5.6.7.1 COBOL for OS/390 & VM

IBM COBOL for OS/390 & VM is generally source-compatible (in terms of the VSAM function provided) with IBM COBOL for VSE. Both compilers provide similar support for VSAM KSDS, ESDS, RRDS, Alternate Index (AIX) path processing, and reusable data sets. Chapter 12, ªCOBOLº on page249 contains more information.

5.6.7.2 OS/VS COBOL

See Chapter 12, ªCOBOLº on page249, for details of DOS/VS COBOL and

OS/VS COBOL migration requirements.

5.6.7.3 RPG II

IBM OS/VS RPG II (5740-RG1) is generally compatible with VSE RPG II (5746-RGI) Release 3. However, OS/VS RPG II is not supported with CICS/OS or IMS/VS HLPI. OS/390 VSAM does not allow an empty cluster to be opened for input; VSE/VSAM permits this operation for SAM-ESDS workfiles only.

5.6.7.4 PL/I

PL/I for OS/390 and PL/I for VSE are essentially compatible in terms of VSAM function, and are generally considered source language compatible.

5.6.7.5 Assembler

For a discussion of Assembler programming considerations, see Chapter 13, ªAssemblerº on page267.

5.6.8 VSAM Error and Reason Code Compatibility

OS/390 VSAM Error codes and reason codes may have a slightly different meaning than VSE/VSAM. In all cases, OS/390 documentation should be consulted such as the DFSMS/MVS DFSMSdfp Diagnosis Reference, LY27-9606. Especially in Assembler, the logic for specific error codes should be verified. In some cases, OS/390 VSAM provides additional information.

5.6.9 DFSORT and VSAM Considerations

Sorting of VSAM files with DFSORT for VSE or VSE SORT/MERGE Version 2 and with OS/390 DFSORT should be compatible with the following two exceptions:

1.Sorting or merging FROM and TO the same (reusable) VSAM data set. (This is often referred to as a suicide sort.)

This function is supported in VSE DFSORT and VSE Sort/Merge, but not supported in OS/390 DFSORT. A suggested circumvention is to sort the VSAM data set to a temporary data set (either VSAM or non-VSAM) and then

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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.
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