There is no equivalent function in OS/390. Many users write their own routine to replace the PAUSE function, if needed, or use the existing automation functions of OS/390.

4.3.4 Allocation of Resources

The allocation of resources in OS/390 occurs at step initialization time. This is a big difference from VSE where allocation of resources occurs at open time. In OS/390, if the JCL contains DD statements that point to data sets, the data sets are allocated even if they are not opened. This makes IEFBR14 useful in testing out allocations or in allocating new data sets.

In MVS, IEFBR14 can be used to run a job with no program execution. This causes all JCL to go through conversion and interpretation. Using IEFBR14 in VSE would not cause a file to be opened, so no allocation of resources could take place.

With MVS, the system allocates the resources when a job step is started. The volumes have to be mounted, the devices have to be available, the system data sets have to be there and the region has to be available. If there are data sets in your JCL, they have to be cataloged and the volume information must be specified. If more tape drives are required than are available to execute the job, the job will wait until sufficient tape drives are made available.

With MVS, the scope of allocation is generally the current step. JCL statements, such as the DD statement, affect only the current job step. This is very different from VSE where the ASSGN statement can secure a tape drive for the duration of the job. In OS/390, a tape drive deallocated at the end of a step may be

²stolen² by another JOB before the beginning of the next step, causing the tape to be dismounted and a mount message to be issued on another tape drive.

4.3.4.1 Resource Allocation at Open Time

With VSE JCL, allocation of resources is done at OPEN time. The JCL can contain numerous DLBL or TLBL statements, even for files that do not exist; as long as the application does not open them, they¢re just ignored. This is completely different in OS/390 where files specified in JCL are allocated at step initiation time, whether the application opens them or not. See item 4 on page 71.

4.3.5 Hidden JCL

Hidden JCL doesn¢t appear in the job stream but is used during the execution of the job. It can be the permanent assignments, labels in the partition or system standard label areas, or ²carryover² (described below).

4.3.5.1 Partition and System Standard Labels

File definitions stored in the partition and standard label areas do not appear in the VSE JCL. In OS/390 all file definitions are coded in the JCL.

System standard labels provide a set of labels that is common to the whole VSE system.

Partition standard labels provide a set of partition specific file definitions. These file definitions are different from one partition to another. This function can be used for application, sort or compiler work files. This may have an impact on

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IBM OS/390 Allocation of Resources, Hidden JCL, Resource Allocation at Open Time, Partition and System Standard Labels
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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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