location for these. In OS/390 these duplicate names need to be resolved somehow. Refer to Chapter 5, ªDisk and Tape Storage Considerationsº on page 97.

4.3.10.9 Conditional JCL

VSE/ESA added conditional JCL processing in the early 1980s, with VSE/SP Version 2. This conditional JCL is characterized by several new JCL statements, including // IF, // GOTO, // ON, and /. LABEL statements which allow the user to make JCL decisions based on the results of conditions set by previous JCL statements and program executions during the job.

The // IF statement can test the value of the last return code, the maximum return code found so far during this job, or the value of parameters. Based on the test, the subsequent statement can be skipped or executed. The // GOTO statement, in conjunction with the /. LABEL statement, allows steps or groups of steps to be skipped. A // GOTO statement will only skip in the forward direction

--looping is not allowed.

4.3.11MVS Job Control Statements

4.3.11.1 DD Statement

The main JCL statement in MVS is the DD statement. It replaces the VSE JCL TLBL, DLBL, ASSIGN, RESET and EXTENT statements. Because it replaces so many JCL commands in VSE it can become complex. One complaint from VSE users is a DD statement must be coded for every step of every job where a file is used. If a change is made to a data set name, the JCL must be changed everywhere the file is used. In VSE these labels may be located in Standard Labels where they can be changed in one place.

4.3.11.2 OUTPUT JCL Statement

The OUTPUT JCL statement was added to JES in release 2.1.3. This replaces the

¢/*OUTPUT¢ JECL statement which provides various output attributes. With the

²DEFAULT=YES² parameter, the OUTPUT JCL statement can provide step level or job level default attributes, much like the JOBLIB, STEPLIB and STEPCAT statements.

See 4.4, ªJECLº on page 89 for more details.

4.3.11.3 MVS Conditional JCL

You can conditionally execute steps in a job by using the IF/THEN/ELSE/ENDIF statement construct or the COND parameter.

IF THEN ELSE ENDIF Statements

Depending on the results of a job step, you might need to bypass or execute later steps. For example, if a step terminates abnormally, you might want to execute an error routine procedure; while if the step terminates normally, you want to continue processing with the next step.

The conditions can be based on return codes, ABEND codes, or whether the job step ran or not.

84VSE to OS/390 Migration Workbook

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IBM OS/390 manual MVS Job Control Statements, DD Statement, Output JCL Statement, MVS Conditional JCL
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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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