Chapter 14. RPG II

14.1 Migration from VSE to OS/390

The aim has been to make it easy to convert programs running under VSE to run under OS/390, with the minimum of changes to the source code. In fact, the source programs will run unmodified, except for the following:

The command level interfaces with CICS/VS and DL/I VSE are not supported by OS/390 RPG II. They must not be specified on the Header Specifications form, and calculations that refer to CICS/VS and DL/I must not be entered on the Calculation Specifications form.

Combined files do not exist in OS/390 RPG II. Such files must not be specified on the File Description Specifications form.

As explained below, many entries that are necessary for an RPG II program to run under VSE are ignored by OS/390. The compiler will issue a warning message, but will still produce object code.

When using spooled print files (JES2/JES3) with overflow printing you must use line counter specification, because channel 12 is not sensed.

Note

As an application development tool, you should consider adopting other application language enabling facilities which tend to take better advantage of S/370 architecture and MVS/XA, MVS/ESA environments; for example, COBOL, PL/I, CSP, FORTRAN.

14.1.1 Device Information

OS/390 allows data management information to be provided at object time by means of DD statements. Parameters such as record and block size, label information, or definition of disk space, can thus be changed without affecting the source code. The entry of these parameters on the File Description Specifications form is optional; JCL specifications are recommended.

Also optional under OS/390 is the definition of physical and logical device; the only device types that must be specified are CONSOLE and SPECIAL.

14.1.2 Print Files

1.For print files controlled by a line counter, without block length specification, RECFM must be specified in the JCL. LRECL is the record length specified in the file description specification plus 1 (for the machine control character).

2.For print files controlled by a line counter with block length specification, the RECFM in the DCB is the file format specified in the file description specification with machine control characters; it cannot be overwritten by JCL.

3.For print files without line control specifications and with block length specified in file descriptions:

© 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.