in your environment. Each should be researched individually for installation applicability.

2.2.2 Subsystem Level Comparison/Affinity

Various sections in this publication deal with the VSE and OS/390 subsystems and detail their similarities and differences. Specifically, these subsystems are:

DB2/VSE and DB2/MVS

DL/I and IMS/DB

CICS/VSE and CICS/ESA

POWER and JES

Telecommunications (VTAM, NCP, BTAM)

ICCF and TSO

Refer to these sections for specific details of subsystem level comparison/affinity and migration issues.

2.3 What Changes Between VSE and OS/390?

The particular items discussed in this section may have some significant impact as you enter the OS/390 environment. How it is decided to implement the changes in these key areas will effect the amount of effort and resources that will be required for the migration and subsequent production environment.

2.3.1 Philosophical Changes

One of the most signification philosophical changes when going from VSE to OS/390 is that of the design points of the two operating systems. OS/390 has at its design point a strong focus on systems management, specifically systems availability. Thousands of lines of operating system code is dedicated to preventing and/or reducing IPLs, system and program ABENDs and unscheduled downtime. This may mean a big change for those VSE environments where frequently scheduled IPLs are a regular occurrence.

2.3.1.1 Security

Customers who have developed security policies and procedures within the VSE environment will find developing similar policies and procedures under OS/390 fairly straightforward. However, as with many of the products providing equivalent VSE function in the OS/390 environment actual product implementation may be different. This applies also to the security product chosen for OS/390. OS/390 focuses on system integrity, that is, security checking is done prior to performing any function.

Customers who have chosen to implement little or no security with VSE may find themselves doing so with OS/390. If this is the case then policies and procedures will have to be developed and a security package, for example RACF, chosen to implement these policies and procedures.

24VSE to OS/390 Migration Workbook

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IBM manual Subsystem Level Comparison/Affinity, What Changes Between VSE and OS/390?, Philosophical Changes, Security

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.