distributed servers. VSE, OS/390, TPF, AIX and others are discovering the enormous value VM/ESA brings to the table.

DB2 Guest Sharing

With DB2, VM, VSE and OS/390 users can now share a DB2 database among several VSE and/or OS/390 guests. For most customers, consolidating several guest databases into one DB2 database reduces administrative work, simplifies operation, increases data integrity, and improves performance. DB2 guest sharing also streamlines access to operational data by decision support personnel, who often use CMS-based tools. Furthermore, sharing one DB2 database gives VSE, OS/390 and VM applications access to remote data by way of Distributed Relational Database Architecture (DRDA) support. Finally, the DB2 VM Data Spaces Support Feature offers even higher performance for users of DB2 Version 3 Release 3 through ESA/390 architecture and VM/ESA Data Spaces.

3990 Models 3 and 6 Fast Write Transparency

VM/ESA makes 3990 models 3 and 6 DASD Fast Write and Cache Fast Write functions available to guests, such as some VSE releases which support 3380/3390s but not the 3990 models 3 and 6 Extended Functions. This allows customers to benefit immediately from moving to the newer storage controllers.

Multiple 3270 Session Support

VM/VSE users often do several things simultaneously on different operating systems. Operators can manage consoles for multiple guest virtual machines, while programmers can move between CMS sessions and virtual test systems. Not surprisingly, users want to be able to run several sessions at each terminal simultaneously to simplify their work. VM/ESA Pass-Through Facility (PVM) supports several concurrent sessions per user with the ability to switch from session to session using a command or hot-key. This function is also available for VM/OS/390 users.

26.3.3.4 Use of CMS

Lastly, it is worth considering the roll of CMS in the migration environment. CMS along with XEDIT and the Shared File System (SFS) provide an excellent environment for managing and modifying the many objects that will need to be moved between the VSE system and OS/390 system. JCL members and other source objects can be moved from the VSE environment and placed into a hierarchical directory structure within SFS. These directories can be accessed by multiple CMS users with complete data integrity ensured. Copies of directories and their contents can easily be made to freeze modification levels for easy backout. Modified objects can then be moved into the OS/390 environment and placed into appropriate partitioned data sets. The CMS environment then becomes the location where modifications are being made. This ensures that nothing in the VSE environment is inadvertently changed wiping out the original contents. In addition it provides a clearing house to quickly see what has been moved to the OS/390 environment if it appears as though critical elements are missing. Lastly, it provides a central location where both old and new copies can be compared side-by-side for problem determination, and tools such as REXX and CMS Pipelines to automate the management and comparison tasks.

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IBM OS/390 manual Use of CMS, DB2 Guest Sharing, Models 3 and 6 Fast Write Transparency, Multiple 3270 Session Support

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.