17.1.2Conceptual Differences between LE/VSE and OS/390 Language Environment

There are some conceptual differences between LE/VSE and OS/390 Language Environment. These differences do not affect the running of your migrated LE/VSE applications in an OS/390 Language Environment but you may want to take advantage of the extra facilities offered by the OS/390 Language Environment. For more information, refer to the LE/VSE Concepts Guide Release 4, or LE/VSE Concepts Guide Release 1, and the OS/390 Language Environment Concepts Guide.

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OS/390 Language Environment supports multithreading. LE/VSE supports only single threading.

OS/390 Language Environment supports applications consisting of one or more processes. LE/VSE supports only a single process for each application that runs in the common run-time environment.

OS/390 Language Environment supports multiple threads within an enclave. LE/VSE supports only a single thread within an enclave.

17.2 VSE to OS/390 Migration Considerations

The strategy you follow to migrate your run-time environment to OS/390 depends on the programming language, the run-time environment you are using in VSE, and the version of VSE you are running.

If you are using an LE/VSE-conforming language, you may be able to transfer your compiled object code to OS/390 from your VSE system, link-edit it with OS/390 Language Environment and run it there without further change. See below for a list of LE/VSE-conforming languages.

Whatever language, run-time environment or version of VSE you are running, you will at least have to relink your object code in OS/390. It is not possible to transfer phases from your VSE libraries to OS/390.

17.2.1 LE/VSE-conforming Languages

An LE/VSE-conforming language is any high-level language (HLL) that adheres to the LE/VSE common interface.

There are three LE/VSE-conforming languages:

C for VSE/ESA COBOL for VSE/ESA PL/I for VSE/ESA

program number 5686-A01 program number 5686-068 program number 5686-069

These languages require LE/VSE to be available at compile-time, as well as link-edit and run-time. LE/VSE requires VSE/ESA version 1 release 4, or VSE/ESA version 2 or later. C for VSE/ESA requires LE/VSE 1.4. You cannot compile or run C for VSE/ESA programs under LE/VSE 1.1.

Any HLL not listed above, is known as a non-LE/VSE-conforming language. These include C/370, DOS/VS COBOL, VS COBOL II, DOS PL/I and VS FORTRAN.

352VSE to OS/390 Migration Workbook

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IBM manual VSE to OS/390 Migration Considerations, 17.2.1 LE/VSE-conforming Languages
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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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