OS/390 systems managed storage (DFSMS) provide enhanced system resource allocation and management. The Hierarchical Storage Manager (HSM), Removable Media Manager (RMM) and basic storage device allocation of OS/390 provide functions not inherent in the VSE environment. However, some of these functions are available from independent software vendor (ISV) products.

1.3.3 Connectivity

Connectivity, that is the ability to connect to other systems, has been one of those areas where VSE support has lagged behind OS/390 and VM. For example ACF/VTAM support for channel-to-channel connections between host systems was not introduced until VSE/AF 2.1.3. Lack of other connectivity support, that is VTAM APPN, SNI gateway, full function TCP/IP and OSA-2, has only added to the reasons why VSE users have decided to migrate to OS/390. However, as mentioned, VSE/ESA has since provided support for some of these capabilities, namely OSA-2 and VTAM APPN. VSE now enjoys virtually all of the same communications and connectivity capabilities as OS/390 and VM.

1.3.4 Systems Availability

Systems availability has always been a strong requirement for many information systems environments. Hardware and software technology enhancements in both VSE and OS/390 have brought about increased system availability. OS/390, however, has had at its core key design elements that give it premier system availability characteristics. Advanced S/390 hardware features coupled with OS/390 software functions give it this outstanding capability. VSE users have found the attractiveness of this enhanced systems availability capability, along with other features, yet another reason to embark on an OS/390 migration.

An example of OS/390 enhanced systems availability is the 3990 Concurrent Copy function when used along with BWO (Backup-While-Open) by DFSMSdss which allows backups to be taken with integrity even when control area and control interval splits and data set additions (new extents or add-to-end) are occurring for VSAM key sequenced data sets. Backup-while-open for CICS VSAM files supports SMS managed data sets without the need to close a CICS VSAM data set or to bring applications down to back up VSAM data sets. This support for backing up VSAM files while open for update is provided in conjunction with MVS Data Facility Product (MVS/DFP).

In the Parallel Sysplex environment concurrent coupling link maintenance allows the replacement of a failing coupling link without powering the CEC down. With DB2 for OS/390 copies of DB2 tablespaces can be made using DFSMS concurrent copy, a process that significantly improves data availability by reducing the time necessary to complete logically consistent copies of

mission-critical data.

Chapter 1. Why Customers Migrate 11

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IBM OS/390 manual Connectivity, Systems Availability
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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.
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