12.4.5.2 File Attribute Mismatches

DOS/VS COBOL file open processing does not always check that the attributes of the file definition in your program exactly match the file attributes of the physical file (for example, as defined for a VSAM file in the LISTCAT). To conform with ANSI 85 requirements, COBOL for OS/390 and VM open processing carries out many detailed checks for consistency between the program and actual file definition before opening the file. This can result in file open failures in COBOL for OS/390 and VM for files that were opened successfully in DOS/VS COBOL. You should add a file status check to your code following each OPEN statement. If these subsequently indicate problems you can amend your program accordingly.

12.4.5.3 ISAM

DOS/VS COBOL supports the processing of ISAM files, however COBOL for OS/390 and VM does not. Any ISAM files should be converted to VSAM Keyed Sequential Data Sets (VSAM/KSDS). CCCA/VSE can automatically convert the file definition and I/O statements from ISAM to VSAM/KSDS.

12.5 Converting from VS COBOL II

If your VS COBOL II source is VS COBOL II Release 4 and has been compiled with the NOCMPR2 option, then it is upward-compatible with COBOL for VSE/ESA, which, as we said earlier, is compatible with COBOL for OS/390 and VM. You can transfer your source code to your OS/390 system and recompile and linkedit it.

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.

However, 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.

There are two new reserved words in COBOL for VSE/ESA, which you may need to consider in your conversion. They are:

∙

∙

PROCEDURE-POINTER FUNCTION

If your VS COBOL II source is VS COBOL II Release 3.2, then, as well as the two reserved words mentioned above, there are three minor COBOL ANSI 85 Standard interpretation changes. These Standard interpretation changes affect the following language elements:

∙

∙

∙

REPLACE and Comment Lines

Precedence of USE Procedures

Reference Modification of a Variable-Length Group

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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.
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