Chapter 22. Librarian

Both VSE and OS/390 have facilities to help you define, organize, and manage libraries of system data. In VSE these system facilities are called the Librarian.

In OS/390, the equivalent function is provided by Partitioned Data Sets (PDS) and the newer Partitioned Data Set-Extended (PDSE), and the group of utilities used for their management, including the Partitioned Access Method (PAM) and the Interactive System Productivity Facility (ISPF).

The following briefly describes VSE and OS/390 library support.

22.1 Overall Library Support

One of the most important utilities in VSE is the VSE Librarian which allows you to back up, restore and re-organize VSE libraries. In OS/390, there are a group of utilities which provide similar functions and capabilities.

Generally, a librarian is a program or a group of programs which serve to organize and maintain the libraries of a system including both system and user program source, object, and load modules. It also contains service functions to display and punch parts of them or display their directories and to set up and change the library concatenation chains and their control tables.

The concept of a librarian is based on the following aspects:

Logical library structure

A VSE library is logically divided into sublibraries. Each sublibrary may contain members of any type (procedures, source books, object modules, phases, user-defined types). This makes a library common for all types of members. Therefore, a component consisting of procedures, source books, object modules, and phases may be put into one library and even into one sublibrary.

In OS/390, a partitioned data set contains a directory and a collection of members. A single PDS (or PDSE) logically corresponds to a sublibrary in the VSE paradigm. It is usual, however, to place members of different types (source, object or load members) into different PDSs in OS/390 environments.

Library data format

VSE library data is blocked, resulting in good utilization of DASD space. The VSE library data format allows space to be reused. Space freed due to deletion of a member is available for reuse without requiring a condense run. The member directories are sorted, improving retrieval times.

Partitioned Data Sets in OS/390 need to be compressed periodically. Use of PDSE structures reduces (or eliminates) this need. Also, PDSE data sets maintain the order of entries in their directories to improve performance compared to PDS structures.

Librarian command language

The VSE Librarian consists of a single program, and its commands follow a consistent pattern. They are powerful and easy to use. They reflect the

© Copyright IBM Corp. 1998

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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.