VM/ESA distribute that communication capability among the guest images using virtual channel to channel devices. Similarly, any DASD that is shared between the VSE LPAR(s) and the VM/ESA LPAR can be defined through R/O minidisk definitions owned by a place holder virtual machine, and accessed through R/O links from the OS/390 guests.

26.3.3.3 The Advantages of Guest Support in VM/ESA

You can use Guest Support in VM/ESA to develop, maintain, manage, and migrate other operating systems that make use of one of IBMs 370, 370-XA, or ESA architectures. System programmers and application programmers often solve the problems they encounter by using the solutions already integrated or implicit in VM/ESA. Some of the reasons customers use VM/ESA Guest Support to run their VSE and/or MVS(OS/390) systems are:

System Simulation Performance benefits

Reduced hardware and migration cost Operations management

Recovery management

Interactive Computing, Application Development and Support Interactive program development tools

Debug and trace tools

Interactive data analysis and reduction Access to VM/ESA CMS applications Server consolidation

DB2 guest sharing

3990 models 3 and 6 Fast Write Transparency Multiple 3270 Session Support

System Simulation

Every computer user has a requirement for a spare system to migrate/upgrade to a new release, try out a new idea or to isolate, debug and test fixes or develop and test new production applications. VM/ESA makes virtually unlimited ªspare systemsº available in virtual machines, each simulating a real machine with very high fidelity. The advantages of making one system look like many need hardly be explained here, but in the present context it is worth mentioning some of them:

With VM/ESAs Guest Support Virtual Machine(s) you can create an exact

replica of your production system on which you can test your new programs, services, and procedures. VM/ESAs Guest Support Virtual Machine is an

extremely cost effective way to have your own test system (or as many as youd like). It is also a safe way to test new function because with VM/ESAs

Guest Support, your test system(s) are contained within a guest virtual machine and securely isolated from your real production system, applications, and data.

Guest Support gives you the flexibility to create a migration plan that fits the needs and schedules of your business. This allows your production systems to remain up during normal business hours, eliminates the work required to schedule, bring down and restore the production system when off-shift work is required. Also, the need to schedule and pay for off-shift programming is eliminated.

You can create a multiple production system environment. For example, your installation might run VSE applications, be migrating to OS/390, and have a

426VSE to OS/390 Migration Workbook

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IBM OS/390 manual Advantages of Guest Support in VM/ESA, System Simulation

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.