cannot be converted entirely automatically, and for which the unresolved conversion requirement cannot be addressed through VSE positioning.

32.5 Conversion Phases

The specific phases included in the Conversion Activities are:

∙

∙

Initial Trial Conversions

OS/390 Regression Tests and Repeated Trial Conversions

The objective of the conversion phases is to automatically mass convert the inventory of production source code and JCL to OS/390, to deliver functionally equivalent OS/390 material (source code, load modules, run JCL, and JCL procedures), and to generate VSE to OS/390 file migration JCL procedures.

The phases end when the quality of the conversion is deemed satisfactory and all critical applications such as daily, weekly, and online applications have been successfully tested under OS/390.

32.5.1 Program Conversion

The mass conversion key steps relative to program conversion are:

Program Conversion Generates OS/390 source code and extract some information required for VSE JCL conversion, such as: files opened, their device types, assignments, block sizes, and open mode (input, output); entry-points; referenced macros, copybooks, includes or sub-programs.

Compilation/Link-EditStarts from the OS/390 version of the source code to generate executable code (load modules).

32.5.1.1 Program Conversion Considerations

The following considerations are recommended to be performed during (or prior to) your migration to OS/390.

∙After all VSE programs are identified and collected for the conversion process, they must be compiled in VSE to detect if there are any source/object discrepancies with VSE production. This ensures that the correct level of the program (source) is used.

∙To be as compatible as possible to OS/390 requirements, VSE programs should be compiled using the latest levels of the VSE compilers. Migration to the Language Environment for VSE and the Language Environment enabled language compilers is strongly recommended.

∙Any VSE program without source code must be rewritten. Products are currently available that will allow source to be recovered (or reconstructed) from executable modules.

∙RPG CICS programs, if any exist, must be rewritten in another high-level language.

∙

∙

∙

All ISAM programs must be converted to VSAM.

BDAM programs must be converted to relative record VSAM where possible.

VSE programs using the UPSI and/or the DATE statement facility will have to have this function simulated in another fashion. In OS/390 either use the EXEC card ²PARM² facility (similar to the VSE PARM parameter introduced in

Chapter 32. Conversion Process 503

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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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