separate operating systems, or the division of tape files and tape volumes between two tape managers running on two separate operating systems.

3.3.7 Standardized Conversion Deliverables and Automation

A significant objective for today′s VSE or OS/390 mainframe installation is the standardization of their application components (JCL streams, application code and data files), associated naming conventions and operation procedures. The standardization of conversion deliverables is directly related to the degree of automation used to perform the conversion. The more automation is used, the more standardized the deliverables will be. Mass conversions are typically more automated than progressive conversions.

It is also much easier to guarantee complete and consistent compliance with standards and naming conventions when the entire inventory is converted and switched from VSE to OS/390 over a single weekend using a single automated conversion process, as in the mass conversion approach. Contrarily, it is difficult to guarantee a good compliance with standards and naming conventions when the conversion of application kernels spans over many months and may be assigned to separate conversion teams, as in a progressive conversion. The same conversion requirement may be addressed differently by different people at different times.

3.3.8 Risk Management

The comparative risk of both conversion approaches has changed over the years.

The risk of disrupting your production system, when dividing it into dual operating environments, has increased in proportion with the VSE application portfolios increase in size, complexity and integration.

With mass conversions, the regimen of performing multiple successful rehearsal conversions has refined the mass conversion approach and its single switchover weekend into a mature and predictable, therefore safer solution.

It is today safer to use the mass conversion approach than the progressive one for large application portfolio, and in some cases of high integration, there is simply no other way.

3.3.9 Complexity of Implementation

Still, the mass conversion approach requires more skills and experience than the progressive conversion approach.

The conversion of one single application kernel requires less integrated automation, therefore less complex (and less expensive) conversion tools. Due to the reduced size of a kernel, it is fairly easy to recover manually from automated conversion defects. The migration of a single kernel requires less planning than the conversion of the entire portfolio. Consequently, the progressive conversion approach has an easier learning curve, which makes it easier to implement with internal non-conversion-expert staff only. They learn while they do it.

Contrarily, the mass conversion approach requires highly integrated automation, therefore complex and expensive conversion tools. Due to the size of the conversion inventory, it is difficult or impossible to recover manually from

Chapter 3. Developing the Plan

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IBM OS/390 manual Standardized Conversion Deliverables and Automation, Risk Management, Complexity of Implementation
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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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