application programs may be placed above the 16 megabyte line if they are written in VS COBOL II, PL/I, C++ or HLASM.

If you have a need to combine systems or you are adding new CICS applications that could introduce additional virtual storage constraints, you should consider the use of CICS Multiple Region Operation (MRO). In addition to providing virtual storage constraint relief, MRO may provide better utilization of multiple processors and improved availability and integrity for your CICS/MVS applications. These benefits are accomplished by the separation of functions into separate address spaces. Note that MRO path lengths will be longer than for a single system image, and there are considerations for operations, recovery, and application design.

A typical MRO system could have one address space for terminal activity (TOR), one for data base activity (FOR), and one or more for application code (AOR). By separating these functions, some problems may be isolated to a single address space (application function). This means that other functions may continue to operate and the time required to restore a lost function may be reduced.

An example of an MRO environment is depicted in Figure 11:

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Figure 11.

Example of an MVS CICS/OS System using MRO

 

Note: CICS TS 1.2 also supports VSAM Record Level Sharing (RLS), which may reduce the need for some FORs.

6.1.5 CICS General System Considerations

As part of the CICS/VSE to CICS TS migration there are release enhancements you should know about before the migration; below are a few to consider.

CICS TS products no longer support: Macro-level programs, BTAM devices and controllers, CICS internal security and signon table, Nucleus load table, Application load table, system generation, journaling to tape, shutdown statistics

136VSE to OS/390 Migration Workbook

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IBM OS/390 manual Cics General System Considerations, Appl, Data Bases, TOR AOR1 AOR2, For MVS

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.