Chapter 16. FORTRAN

16.1 VS FORTRAN in OS/390

VS FORTRAN is the compiler and library to use on OS/390. VS FORTRAN expands greatly on what you can do with FORTRAN in accessing system services and/or hardware features. If you have used VS FORTRAN on VSE, you may be aware of the extensions that VS FORTRAN provides over DOS FORTRAN, such as execution time dynamic commons, compile-time included source files, asynchronous I/O, and level 66 language compatibility. VS FORTRAN has multitasking on OS/390, and the Version 2 product offers programming enhancements such as structured programming constructs, long variable names, an Intercompilation Analyzer, and an interactive full screen debugger. In Version

2Release 3, data-in-virtual support and dynamic file allocation are available. The Version 2 product also supports the IBM 3090 vector hardware, and it also conforms to the SAA Common Programming Interface (CPI).

16.2FORTRAN Conversion Considerations

The conversion to OS/390 means that some changes are needed to certain DOS FORTRAN programs. First, the OPSYS routine is no longer supported. The I/O services and more are supplied in Version 2 Release 3 with dynamic file support. The overlay support provided by OPSYS is no longer needed, because now larger programs are supported in the 2 Gigabyte address spaces supported by OS/390. Options that were used before to control compilation are now handled in part by cataloged procedures and in part by the compiler options VS FORTRAN now recognizes. VS FORTRAN also now allows execution time options to control the running of your production programs.

Although recoding of programs is not necessary except for routines using OPSYS, the benefits to your programs can be measured in increased performance due to the many optimization levels the compiler provides. Exploitation is available to recompiled programs so that they may now run above the 16MB line. Access to the vector hardware is available through recompilation as is access to new operating system features.

© 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.
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