The selection of a particular option of MVS may require redesigning the application programs. In addition, a program logic change may also be forced by attempting to simulate a VSE function under MVS. Examples of these possibilities include multitasking, interrupt handling, and communication region accessing.

The input and output components of the linkage editors, the job control language, and linkage edit control statements necessary to build program structures are discussed in the publication DFSMS/MVS Program Management, SC26-4916.

VSE assembler language programs that are changed to MVS must add an initialization routine to meet MVS requirements. You should establish a standard for the entire installation that can be simply inserted into the assembler language source member before it is recompiled under MVS. For additional information on the MVS services and macro coding details, refer to the following publication:

∙OS/390 MVS Programming: Assembler Services Reference, GC28-1910.

For Data Management programming macro information, refer to:

∙

∙

DFSMS/MVS Using Data Sets, SC26-4922.

DFSMS/MVS Macro Instructions For Data Sets, SC26-4913.

Important

The macro functions and parameters described in this text may not be totally up-to-date. Macro facilities change over time. New macros and macro parameters become available with new releases of products. Therefore, you should always reference the appropriate macro manuals (listed above) for exact macro functions and applicable parameters. (Even though some macros may not be up-to-date, the techniques illustrated here should still be applicable.)

The next section highlights the services provided by the MVS supervisor and relates them to comparable ones provided by VSE. Information on VSAM macros is found in the section 13.2.5, ªVSAM Macrosº on page 290. Data Management macro comparisons are addressed in the section 13.2.6, ªData Management Macrosº on page 292.

13.2.1 System Interface and Macros

The functions of the VSE system interfaces and macros and their MVS equivalents are discussed in the following text.

MVS Register Conventions

Application program use of general purpose registers in MVS is restricted to registers 2 through 12. (Registers 0, 1, 13, 14 and 15 are used for special purposes by MVS - see next sections.) If VSE programs use other than registers 2-12 for application purposes, program register assignments may have to be changed.

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IBM OS/390 manual System Interface and Macros, MVS Register Conventions
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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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