For unlabeled tapes - the DEVADDR is the only link between the program and the JCL (there is no TLBL). Either the DEVADDR or the DTFname can be used as DDNAME.

For card devices - the DEVADDR links the DTF to a card reader or puncher; Either the DEVADDR or the DTFname can be used as DDNAME.

For print devices - the DEVADDR is the only link to a printer or a LST card. Either the DEVADDR or the DTFname can be used as DDNAME.

4.3.7 Catalogs

With the exception of VSAM, in VSE JCL there are no catalogs to deal with. The user must provide an extent for each read or write to a disk file.

For tape functions the correct tape must be mounted. Volume information must be specified for disk files using an EXTENT card, except for files managed by VSAM, which are managed in a VSAM catalog.

There are vendor products in the marketplace that provide these cataloging functions, such as Dynam and EPIC. Many VSE installations use one of these products for disk management, tape management, or both. Installations that do not use a third-party disk manager often make extensive use of VSAM-managed SAM files.

4.3.8 Partition Dependent Codes in JCL

4.3.8.1 Procedures

Partition-dependent codes in VSE JCL can ensure that a procedure runs in a particular partition. Procedures may be cataloged names in the form of $xABC (where x = 1, 2, 3,... B = representing BG, F1, F2, F3,... FB partitions). A job may be built with an EXEC PROC=$$ABC and run in various partitions. When run in BG, $0ABC.PROC will run; when run in F5, $5ABC.PROC will run; and so on. MVS, which has no notion of ²partition², has no equivalent function.

4.3.8.2 Data Set Names

Data set names can contain the condition dependent operands; ¢ % % ¢ . The first

¢% ¢ is partition, the second ¢ % ¢ is the view.

This function is similar to the DSN=&&dsname function in MVS, which allows use of the same JCL in concurrently running jobs without having conflicts with the data set names.

4.3.9 Communication Region - DATE and UPSI

4.3.9.1 DATE

In VSE, the date is stored in the Job Date field of the partition¢s communication region. There is only one facility in VSE from which to get the date. The date can be entered in the JCL and is what the job will see whenever the application queries the system date. The result will be the date that is specified in JCL.

The VSE DATE function allows a job to run with a date that is not the system date. It can also ensure that when a job that takes an hour to run is started at 23:30, the steps that execute after midnight will maintain the same date.

Chapter 4. Job Control Language (JCL) Differences and Considerations 81

Page 105
Image 105
IBM OS/390 manual Catalogs, Partition Dependent Codes in JCL, Communication Region Date and Upsi

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.