Customization and Programming, Resource Definition

without disruption. Sessions are simply taken over by a new copy of the application running in the same, or a different, processor.

9.1.2.1 Resource Definition

The OS/390 VTAM resource definitions are stored in the VTAMLST data set. Most of the VSE/VTAM resource definitions (B-books), typically stored in the PRD2.CONFIG VSE library, can be moved directly into the VTAMLST data set without modification. There are several items worth noting here:

∙If migrating from VSE/VTAM V3R4 or older, MVS and VSE will differ in their use of VTAM buffers. VSE/VTAM V3R4 utilizes the LFBUF pool for I/O and two unique fixed size buffer pools (VFBUF and VPBUF) for pool expansions. VFBUF defines storage for expansion of fixed storage buffer pools and VPBUF for expansion of pageable storage buffer pools. VSE/VTAM V4R2 storage pools and usage was designed to be similar to MVS/VTAM. VFBUF and VPBUF buffer pools were eliminated and the IOBUF buffer pool was added for I/O. IOBUF size should be matched to NCP (UNITSZ) buffer size and tuned for your requirements. All the other OS/390 buffer pool definitions have reasonable defaults and can usually be left alone until it is time for fine tuning.

∙If you are converting a Token-Ring ICA attachment to a 3172 or OSA attachment, you will need to replace your Local Area Network (LAN) major node with an External Communication Adapter (XCA) major node to define the connection.

∙Where the VTAM definitions refer to a data set, the coding often changes. This mainly occurs in NCP definitions; please refer to 9.2, ªACF/NCPº on page 192 for details.

9.1.2.2 Operation

Most of the OS/390 VTAM console commands will be familiar to the VSE operator. One point of interest is that the DISPLAY, VARY and HALT commands are VTAM commands so that they take the format D NET..., V NET... and so on. On the other hand, START and MODIFY are OS/390 commands so they must refer to the actual name of the VTAM start procedure. Thus if VTAM is started using S NET28,,,(LIST=S0) then a subsequent MODIFY command will appear so (for example) F NET28,TRACE,....

9.1.3 Customization and Programming

VTAM tuning can be quite different under VSE and OS/390. Matters such as optimizing I/O across a channel and pacing the flow of traffic are very similar, but OS/390 VTAM uses storage and buffer pools in a completely different fashion than VSE, so this aspect of tuning needs to be reviewed in some detail. Please see the chapter Tuning VTAM for Your Environment in the Network Implementation Guide for advice on tuning OS/390 VTAM.

9.1.3.1 VTAM Tables

Most of the VTAM tables which are assembled and linked do not differ between OS/390 and VSE, but the use of mode tables needs to be considered.

VSE provides a VTAM mode table called IESINCLM. It is a subset of the default VTAM mode table (ISTINCLM) but also contains some unique entries. IESINCLM is routinely used in VSE systems, but is not provided by OS/390 VTAM. Migration of the table and/or unique entries may be required. Refer to the VSE/ESA Networking Support manual for more information on IESINCLM.

190VSE 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 manual Customization and Programming, Resource Definition, Operation, Vtam Tables

Models: OS/390