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IBM OS/390 manual Job Control Language JCL Differences and Considerations

Models: OS/390

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Chapter 4. Job Control Language (JCL) Differences and Considerations

The following sections describe the major tasks and considerations involved in converting VSE JCL to MVS JCL and the differences between them. These sections are divided into the following categories:

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4.1, The Philosophy of JCL in System/390

4.2, High Level Similarities

4.3, JCL Differences Between VSE and MVS

4.4, JECL

4.5, VSE and MVS JCL Comparison Example

While this chapter describes the differences and conversion tasks, we recommend that you take a class on MVS JCL. See Appendix A, ªEducation Informationº on page 535.

4.1 The Philosophy of JCL in System/390

Often, before discussing JCL systems and schemes, it is valuable to understand why the System/390 (originally the System/360) operating systems incorporated Job Control.

In the era of the predecessor computer systems, for example the IBM 1400, 7080, and 7090 systems, the concept of job control was just beginning. Application program coding included explicit references to files and other system resources. If a given program could be used with another file, the program often required changes. Flexibility and the beginnings of resource reuse led to the concept of a system facility that externalized the references from programs to other system resources, whether they were other programs or data files.

Job Control Language was developed as part of the System/360 architecture, to address the requirement for reuse. The ability to use one program with different files, and with different predecessor and successor programs, makes computer programs much more usable. This ability to create jobs and steps is crucial to the development of today¢s ²Industrial Strength² information processing technology.

As OS/390¢s predecessors were being developed, it became obvious that the smaller customers¢ needs required smaller systems. With the economics in the information processing over 30 years ago, the smaller systems were too small in terms of internal and external storage and processor power to provide the minimum environment needed for OS/360.

VSE/ESA¢s predecessors were developed to permit smaller customers¢ requirements to be met with the smaller systems then available. BOS (Basic Operating System), TOS (Tape Operating System), DOS (Disk Operating System), DOS/VS, VSE, and now VSE/ESA are the progression of operating systems designed to ²fill the hole² left by small processor requirements that could not meet the minimum resource requirements of the OS/390 predecessors.

© Copyright IBM Corp. 1998

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IBM OS/390 manual Job Control Language JCL Differences and Considerations, Philosophy of JCL in System/390
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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.