8.1.5.10 Assembler Language Calls

CALLDLI MF=E is not supported in IMS/ESA.

8.1.6 Utilities

Equivalents of all DL/I utility programs exist in IMS/ESA. Their functions are similar, but it is necessary to change the JCL from VSE to MVS and utility control statements from DL/I to IMS/ESA. There are variations in the utilities between DL/I and IMS/ESA that will require procedural changes.

Partial HD Reload is not supported in IMS/ESA.

Selective HD Unload is not supported in IMS/ESA.

Similar function is provided by the IMS System Utilities/Data Base Tools (5685-093).

8.1.6.1 Rewind Option for Reorganization Utilities

This is controlled by JCL in MVS. The VOLUME parameter on the tape DD statement allows you to specify whether or not the tape is to be dismounted. The LABEL parameter indicates how many data sets precede the required data set on the tape volume.

8.1.6.2 Checkpoint Option with HD Reorganization Unload Utility

In IMS/ESA, checkpointing is requested through the DFSUCKPT DD JCL statement. Restart requires the DFSURSRT DD statement as well. See the IMS/ESA Utilities Reference: Database Manager manual for more information.

8.1.6.3 Secondary Index Creation

In DL/I the secondary indexes are created when the data portion of the database is loaded. DL/I will create a secondary index during load, HD reload, or prefix update. IMS/ESA uses the HISAM unload and reload utilities to create the secondary indexes from a work data set created by the prefix resolution utility. The Prefix Resolution and HISAM unload and reload utilities are run after the data portions of the database have been created. Refer to the IMS/ESA Administration Guide: Database Manager and the IMS/ESA Utilities Reference: Database Manager manuals for the reorganization of databases with secondary indexes or logical relationships.

8.1.7 Operations

8.1.7.1 RESTART with CHKP

If you are using CHKP in your DL/I batch jobs and have developed procedures for restarting that are acceptable to MVS, do not make any unnecessary changes at this time. If your existing procedures require more than minimal conversion effort, you should consider the use of the IMS/ESA symbolic checkpoint and IMS GSAM. All new IMS/ESA applications should use the symbolic form instead of the basic form of CHKP. One exception would be applications using CICS/OS Shared Database.

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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.