in the VTOC. This equivalent function is performed in OS/390 VSAM by the AMS command ALTER REMOVEVOLUMES.

The volume cleanup function of ²ALTER REMOVEVOLUMES² should only be used when the catalog is not accessible or totally unavailable. This command may also be used to remove candidate volumes as in VSE/VSAM.

IKQVCHK - Catalog Check

This VSE/VSAM utility does not exist in OS/390 VSAM. The AMS DIAGNOSE and EXAMINE commands provide an equivalent function.

Space Classes

Space classes of VSAM data spaces are not supported by OS/390 VSAM. However, VSAM files, data spaces, or volumes established under VSE/VSAM with space classes can be processed by OS/390 VSAM as long as the VSAM catalog is supported (December 31st 1999).

VSAM SHAREOPTIONS

Since VSE and OS/390 use totally different implementations for data set sharing and control, they provide no protection from each other through any of the VSAM shareoptions. There are significant VSE and OS/390 differences in the access and protection provided by shareoptions three and four.

Shareoptions one and two (SHR(1) or SHR(2)) function exactly the same in VSE/VSAM and OS/390 VSAM. SHR(3) and SHR(4) provide cross-partition (or cross-address space) and cross-system access to VSAM files. These will be discussed in the next section of this chapter.

VSE/VSAM SHR(4) was used by CICS/VSE to allow CICS applications to update a VSAM data set through both the base cluster path and alternate index (AIX) path, prior to the availability of data set name sharing in VSE. Data set name sharing became available in VSE/ESA 1.3. This is not necessary with CICS/OS/390. CICS/OS 1.7 or later uses OS/390 VSAM data set name sharing to allow these updates, with integrity. Note that both the base cluster and AIX(s) must be in the same VSAM LSR buffer pool or use NSR buffer pools.

5.6.6 Data Sharing and Integrity

You should read this section very carefully. There are significant differences in the cross-partition or cross-address space and cross-system protection provided by VSE and OS/390 VSAM shareoptions. OS/390 VSAM SHR(4 x) or SHR(4 4) provides less automatic protection than VSE/VSAM. Applications that use

VSE/VSAM SHR(4) or SHR(4 4) protection or VSE DASD sharing protection must be carefully evaluated in light of the differences in protection provided by OS/390 VSAM. For more details, refer to DFSMS/MVS Using Data Sets,

SC26-4922. In a parallel sysplex environment, Record Level Sharing (RLS) can be used to access VSAM data sets instead of shareoptions. RLS provides complete integrity.

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IBM OS/390 manual Data Sharing and Integrity, Ikqvchk Catalog Check, Space Classes

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.