the conversion of the JCL which may have to be converted differently, depending on in which partition the job normally runs.

There is no equivalent to standard labels in OS/390. Labels must be spelled out in each step. One way to keep a common set of labels in OS/390 is to use the JCL INCLUDE statement. In rare cases another possibility is to use dynamic allocation to replace standard labels.

4.3.5.2 Permanent Assignments and POWER Defaults

Readers, punches, printers or disks can be permanently assigned in VSE. These assignments do not appear in the individual job JCL. OS/390 does not use the concept of a permanent assignment.

Spool devices can be started at POWER initialization time. They can also be stopped or started by the operator from the Attention Routine. This also does not appear in the JCL.

4.3.5.3 ²Carry-Over²

Carry-Over is a user term for a phenomenon that exists in VSE JCL and is otherwise undocumented. Carry-over occurs where a job step has tape or disk file definitions with DLBL or TLBL and there are additional execute statements. These execute statements will have access to these file definitions which are in a previous step. This can occur as long as this is not a new job and there are no intervening DLBL or TLBL (see 4.5.3, ªSample VSE plus Carry-Overº on

page 94).

One common method in VSE is to put all the file definitions at the top of the job and then all that remains is the execute statements. The problem this creates is with translation, as it is difficult to associate the program with the file it uses.

The conversion task is to translate the programs to identify what files are used. The output is to produce a table or listing that has the file information and then merge the information with the JCL. It is a process of submitting all job steps and removing one level after the other to see which one is used and which one is not.

The opposite is also true in that some of the JCL may never be used. TLBLs and DLBLs may be present that are never used by that job or are used infrequently.

4.3.5.4 Help for the Hidden JCL Problem

Recent releases of VSE/ESA (Version 2.2 and later, and Version 1.4 and 2.1 with maintenance added) provide additional functions which can help with the Hidden JCL problem. The availability of Opti-Audit for VSE (also available from Barnard Software, Inc. as well as a part of the VSE/ESA Version 2.2 system) provides the ability to track usage of VSE program resources by job and job step, and of files by program or job step and by job. Opti-Audit can also collect inventory data from a running VSE/ESA system including the resources allocated through Standard Labels, Permanent Assignments, POWER defaults, and carry-over.

Another new function is called the VSE/ESA JCL Analyzer, which consists of a group of programs and files which gather file usage information from a running VSE/ESA system, and use that data to create an output file suitable for processing by the VisualAge tools on a workstation. The Application

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IBM OS/390 manual Permanent Assignments and Power Defaults, 5.3 ²Carry-Over², Help for the Hidden JCL Problem
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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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