procedure in order to apply jobset maintenance concurrently with maintenance to VSE production.

32.6.2.2 Final Program Conversion

There are two key tasks associated with the translation and compilation of all the VSE source materials for the final program conversion. First is the final mass translation with the objective to translate all of the source modules in their current state, overnight, automatically, and without errors. Second is the mass compilation for the final conversion. The objective of this task is to compile and link-edit all of the translated source modules overnight, automatically, and without errors.

32.6.3 Switchover

The switchover weekend may not be a typical weekend, because it is a period when operations are interrupted for the switchover. This interruption may be for as little as a few hours or for as much as one or two days. Before switchover, the production workload runs under VSE. After switchover, the production workload runs under MVS.

The objective here is to switch VSE production over to MVS and continue operations under MVS.

This transfer must be:

∙sufficiently fast to allow mass switchover to take place within the allotted time

∙in conformity with the generated MVS JCL to avoid modification during the initial runs

∙complete, because you should avoid coexistence of VSE and MVS systems.

In addition, backup operations on the VSE side are necessary before file transfer to provide for a possible return to VSE in an emergency or for a recovery of overlooked files. Backup operations on the MVS side are necessary to permit recovery, if required, during initial MVS operations.

Switchover weekend activities include terminating VSE operations, backing up the VSE and OS/390 environments, switching the network, executing file migration and cataloging procedures, starting OS/390 operations with CICS transactions and jobs according to normal weekend schedule, and supporting OS/390 operations through review and resolution of exceptions. On Sunday, the switchover is validated (stay under OS/390) or VSE fall back procedures are implemented (return to VSE in case of unexpected difficulties).

32.6.3.1 Data/File Migration

On switchover day you have to have all of your data available to your new system. This process of multiple dress rehearsals of switchover gives the whole team confidence about the final switchover. At that time the team has been through it many times.

Chapter 32. Conversion Process 517

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IBM OS/390 manual Switchover, Final Program Conversion, Data/File Migration
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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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