OS/390 production is realized at an early time in the migration.

When the first kernel is completed it is cut over to OS/390 production. This could be at a very early time in the migration thus providing early OS/390 feedback.

However, this may not be the advantage it appears to be. Dual OS/390 and VSE production environments exist as VSE production (of unconverted kernels) is required. This can be a disadvantage operationally as well as cause problems in resource (I/O) scheduling.

Many times, because of the dual production environment, application bridges must be built (special procedures) to allow data and catalogs to be alternately processed by the OS/390 and then the VSE system. Also, maintenance and development activities must be performed on both systems, thus potentially slowing down the overall migration.

Dedicated and rotating conversion teams are usually involved.

The system programmer contingent of the conversion team is mainly dedicated to the migration effort. However, application programmers very often are involved in converting their own applications with this approach. Rotating application programmers in and out of migration efforts can be detrimental to development activities. It can also slow down overall effectiveness of the migration as additional time and training takes place each time new personnel are assigned to the conversion team.

No definite project-end date is likely to be associated with this approach.

Many times with the kernel approach, the conversion effort ²runs out of steam² before the project is completed. This happens after the important bread-and-butter kernels are cutover. Then, priorities often change and the lesser visible applications stay operational under VSE for long periods of time. This becomes expensive to a company as additional resources are involved in maintaining two operating systems and managing two production environments. This is why the phrase ²it took us 18 months or two years² is many times muttered about a VSE to OS/390 migration.

2.5.2.2 Single Switchover - Mass Application Migration Approach

In the single switchover - mass application migration approach, all applications are cutover to OS/390 production at the same time. (This time is often referred to as the ²switchover².) As applications are converted and successfully tested under OS/390, they are ²shelved² until switchover. 4 At switchover, VSE operations stop in entirety and OS/390 operations commence. A comprehensive conversion aid tool (that is, product) is almost always used with this approach. Some of the advantages to the single switchover - mass application migration approach are:

OS/390 operations are deferred until project completion.

The advantage of this is that there is no dual operations. Operators run VSE production until the conversion is over. Also, there are no special ²bridges² that have to be built between the two systems since there is no need to move production data back and forth between VSE and OS/390 systems.

A dedicated conversion team is usually associated with this approach.

4Maintenance updates can continue to be made to these ²converted² VSE applications. The changes should be made to the VSE source programs. Later these programs will have to be cycled back through the conversion process.

28VSE to OS/390 Migration Workbook

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IBM OS/390 manual Single Switchover Mass Application Migration Approach

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.