names. This is because naming conventions can facilitate or impair the implementation of OS/390 system components (such as DFSMS) and other automated operations tools. It is recommended that you understand how a production item will be stored, used and managed under OS/390 before giving it a name.

Because new OS/390 JCL streams will be generated, new rules are developed to define the structure of those streams, and how repetitive JCL statements will be regrouped into procedures or includes in order to facilitate future JCL maintenance. For example, a dedicated JCL procedure may be used for each of the highly repetitive utility steps (SORT, IDCAMS, and so on), and compiler or debug related DD statements (SYSOUT, SYSUDUMP, and so on) may be regrouped into a single JCL include. The storage and management of control cards and their reference from the JCL is another set of rules associated with the structure of JCL streams, as is the usage of execution parameters and their transfer from production control clerk to executing program through job scheduler and JCL symbolic parameters. It is recommended that you not redefine the division of batch applications into job streams, because this would impact the job scheduling rules and confuse operations personnel.

As part of the OS/390 migration, the usage of utility steps can be redefined. It is typical to find half a dozen ways of performing the same file copy in the VSE JCL. Only a couple of ways may be needed and retained in the OS/390 JCL. The same standardization applies to other file utility steps, such as external sorts and backups. Database application steps and database utility steps are also standardized, and some of the associated JCL may be isolated in JCL includes or procedures for easier maintenance. Service steps of all kinds may be inserted automatically by the mass conversion JCL generation tools, for example to delete catalogued temporary files.

System managed storage is very strongly recommended when it comes to file management under OS/390. One of the great combined advantages of DFSMS and DFP is that they allow drastically simplified DD statements, which makes JCL very easy to read or maintain, and be configuration independent. Typical OS/390 migration standards include the elimination of VOLSER, RECL, BLKSIZE, RECFM, ORG, DSCB, SPACE and UNIT attributes (with the exception of RECL in IDCAMS/REPRO output and UNIT for tape file output).

Many VSE sites tend to be tape oriented. The OS/390 migration is an excellent opportunity to migrate from tape intensive to disk intensive operations, eliminating many manual interventions (for tape volume mounts) and boosting job throughput as a result. DFSMS¢s automated free space release and HSM¢ s archival features can be combined to implement disk space ²buffering² techniques, in which files that will end up on tape are created on disk by the executing job. The copy of the file to tape, as well as the accumulation of many files on the same tape volume is left to HSM. It takes place after the job execution is completed. Once again, the effect is a drastic reduction of manual interventions for tape mounts, as well as an acceleration of the job throughput. Such file and device management policies are part of the standards and operations procedures definition in an OS/390 migration. They have an enormous effect on the structure and content of JCL streams.

New names must be defined under OS/390 for all items referenced in the new OS/390 JCL, including data sets, jobs, procedures, includes, steps, execution parameters, libraries of any kind (from source or executable code to procedures

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IBM manual VSE to OS/390 Migration Workbook

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.