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IBM OS/390 manual Miscellaneous Functions, Data Set Naming Considerations VSE Considerations

Models: OS/390

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In OS/390, the application program linkage is handled through the SVC interfaces of the operating system.

In either case, the application program functional request (GET, PUT, and so on) will cause the next logical record to be retrieved from a buffer or from external media. Channel programs are created, and the operating system will cause the channel programs to be scheduled to perform any physical I/O operations required by the functional request.

5.1.3 Miscellaneous Functions

In VSE and OS/390 environments, access method OPEN logic is responsible to ensure that the user is authorized to access the data in the file being OPENed. This includes label (Data Set Control Block or DSCB) checking for input files, and checking to ensure that the output file does not overlay existing files. In addition, the access method (and operating system) is responsible for error handling and recovery where possible only notifying the application program when unrecoverable errors occur.

In OS/390, the access method will interface with the operating system Direct Access Device Space Management (DADSM) component to manage allocation of space as required. In VSE, this function may be done through VSE/VSAM Space Management, an OEM vendor product, or manually through JCL specifications.

5.2 Data Set Naming Considerations

5.2.1 VSE Considerations

It is common in VSE shops to have loose data set naming standards. System files may be named in a standard fashion, but application files will be named depending on the programmer or implementer of the application. Identifying files by application or subsystem from their name may be difficult, and knowledge of how one installation has named their files will be of little use in another installation.

For non-VSAM files, the format of file-ids (between the apostrophe characters) is not defined by the system. One continuous string of up to 44 characters may be defined as the file-id for a disk file using the VSE DLBL JCL statement.

In most VSE shops, this will provide little problem -- a rare case of aggravation, at most, and then only rarely. This is not the case in OS/390 environments, however.

5.2.2 OS/390 Considerations

In OS/390 environments, the connection identifying which user catalog contains the management information for a given file or data set is dependent upon OS/390′s ALIAS mechanism. Further, the specific requirement for at most eight characters between periods in any data set name (DSN) is enforced. Each string of characters (node) must start with an alphabetic or national character, and the system uses the high order (left-most) node to identify which user catalog contains the catalog information for the data set in question. The system′ s MASTER catalog contains the list of ALIAS definitions together with the user catalog associations.

Chapter 5. Disk and Tape Storage Considerations 99

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IBM manual Miscellaneous Functions, Data Set Naming Considerations VSE Considerations, 2 OS/390 Considerations
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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.