12.5.1 VS COBOL II CICS Programs

COBOL for OS/390 and VM and OS/390 do not support CICS macro-level programs. If you have any programs written in macro-level CICS you must convert them to command-level CICS.

If you need to change your programs to cater for these differences, you can do so before you migrate them to OS/390. Then, if you prefer, you can transfer the compiled object code to OS/390 for linkediting. See 12.2, ªVSE to OS/390 Migration Considerationsº on page 250.

12.6 Converting from COBOL for VSE/ESA

If you are converting from COBOL for VSE/ESA then, with one exception, your source will be compatible with COBOL for OS/390 and VM. You can transfer your source code to your OS/390 system, recompile, and linkedit.

If you prefer, you can transfer the compiled object code to OS/390 for linkediting. See 12.2, ªVSE to OS/390 Migration Considerationsº on page 250.

The exception is that if you are using LE/VSE callable services you may need to change their names. Callable services which have names in LE/VSE beginning with CEE5.... are named CEE3.... in OS/390 Language Environment. These names

will require changing and these programs will have to be recompiled in OS/390. You will not be able to transfer the compiled object code for these programs to OS/390. Refer to Chapter 17, ªLanguage Environment (LE)º on page351 for more information about migrating your run-time to Language Environment.

12.7 Some Conversion Considerations for all VSE COBOL Compilers

This section discusses some differences in the behavior of COBOL programs under VSE and COBOL for OS/390 and VM.

12.7.1 VSAM

Under VSE, if a VSAM file is not closed at the end of a program for any reason, (for example, no CLOSE statement in the program, or the program ABENDs), VSE will attempt an automatic close of the file. In this case, when the file is next OPENed, the file status code will be 0.

Under OS/390, if a file is not closed at the end of a program, the next time it is OPENed, OS/390 will perform an implicit VERIFY on the file, and successfully open the file. However, the file status code returned in this situation will not be 0, but 97.

Therefore, if your programs check for a successful OPEN, based on a file status code of 0, you should also check for a file status code of 97.

12.7.2 DISPLAY Statement

Under VSE, output from DISPLAY statements is interspersed with output from

WRITE statements, and your programs may be coded to take account of this.

This does not happen in OS/390, as OS/390 has the ability to produce multiple print files and you should make use of this facility.

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IBM OS/390 manual VS Cobol II Cics Programs, Converting from Cobol for VSE/ESA, Vsam, Display Statement

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.