OS/390. Therefore, it is not required to freeze or follow up development, enhancement, or maintenance of applications during the conversion.

32.2.2.3 Mass Conversion (Switchover)

The actual mass conversion, called the switchover, often takes place over a single weekend. Before switchover, the production workload runs under VSE. After switchover, the production workload runs under MVS.

The switchover is the key advantage of using Cortex-MS as a conversion tool. It eliminates the migration problems related to running some applications under VSE and some under MVS for an extended period of time. It eliminates the need to maintain both MVS and VSE versions of files. It allows maintenance and development work to be done on the VSE versions of programs right up until the actual mass conversion, and the program converted is the latest working VSE version.

32.2.2.4 Automation Limits

Some non-standard source code modifications must be performed manually, either because they are too complicated to automate, or because they are in very low occurrences. In both cases, automating the process would not be cost effective when compared to a manual modification. Manual modifications complement the automated conversion (before or after). They can be applied as VSE positioning, or manual OS/390 conversion.

Modifications applied to the VSE version of the source code, which is then tested and installed in production under VSE is known as ²VSE Positioning². This technique is consistent with the repetitive conversion approach because it does not require freezing any source code. For example, VSE COBOL programs must be manually positioned to:

Move STOP RUN statements outside INPUT (or OUTPUT) SORT PROCEDURE,

Remove any access to I/O buffers before the file is opened or after the file is closed,

Remove some undocumented features of COBOL Report Writer,

Remove the use of the DISPLAY verb to imbed lines into a report written with the WRITE verb.

Modifications applied to the OS/390 version after automated conversion are known as ²OS/390 Freeze². Here a procedure is defined to automatically identify and manually duplicate the VSE maintenance to the OS/390 ²frozen² source code throughout the project. Manual OS/390 conversion is limited to exceptions because it is incompatible with the repetitive conversion approach.

After switchover, all production is done with the MVS versions of your applications. The programs that Cortex-MS translates become genuine MVS programs and are not emulated.

32.2.3 Mass Conversion Tools

Software tools suitable for mass conversion must automate most of the conversion of VSE JCL, programs and files to native OS/390 without any custom modification.

In addition, to accommodate the large diversity of coding patterns between VSE sites, the mass conversion tools must be flexible. Run-time options and exit

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IBM OS/390 manual Mass Conversion Tools, Mass Conversion Switchover, Automation Limits

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.