Statement Compatibility, Field Level Sensitivity

8.1.5.4 Statement Compatibility

All batch programs using the calls, GU - GHU - GN - GHN - GNP - GHNP - ISRT - DLET - REPL, are transportable to MVS with no modification to the DLI calls. Of course, these programs may need changes for other reasons and they must be recompiled on the MVS system. VSE JCL is changed to MVS JCL, and the DL/I parameters external to the program (that is, HSBFR and HDBFR bufferpool) are written differently even though they perform the same functions. They are defined in the IMS/ESA control data set DFSVSAMP. This is described in the IMS/ESA Installation Volume 2: System Definition and Tailoring manual.

The languages common to DL/I and IMS/ESA are PL/I, COBOL/VS and Assembler. RPG II is not supported by IMS/ESA, but RPG/370 is.

The status codes tested with DL/I are valid with IMS/ESA and have the same meanings with some exceptions which are covered below.

8.1.5.5 Field Level Sensitivity

Basic support is compatible between DL/I and IMS/ESA. If DL/I extensions are used, changes may be required to application programs as well as to database definitions. Status codes starting with ′K ′ will not be returned by IMS/ESA.

8.1.5.6 PCB after GE Status

There is a difference in the information returned with the GE status code following a number of GNP calls. In DL/I the segment name returned is that of the last successfully retrieved segment. In IMS/ESA, the segment name returned with the GE status code is that of the parent segment.

8.1.5.7 NI Status Codes

DL/I requires a user to manually correct a database following an NI status code. IMS/ESA automatically fixes this error condition.

8.1.5.8 CHKP Calls

While the written form of the CHKP call is the same, the PCB-name specified in IMS/ESA must refer to the first PCB in the PCBLIST. This PCB is called the I/O PCB and is generated with the CMPAT option in PSBGEN. Since this is a new PCB, application programs will have to be changed to reflect the existence of this PCB.

8.1.5.9 GSCD and/or GSTA Calls

These must be reviewed for the following reasons:

1.GSCD has a common format and returns the address of the SCD area. However, the SCD DSECT layout is not the same and label names may differ.

2.DL/I supports the GSTA call for application programs running across separate VSE/VAE address spaces. This allows access to DL/I statistics when DL/I Multiple Partition Support (MPS) applications are running in separate VAE address spaces. The IMS/ESA STAT call provides similar functions.

172VSE to OS/390 Migration Workbook

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.

IBM OS/390 Statement Compatibility, Field Level Sensitivity, PCB after GE Status, NI Status Codes

Models: OS/390