7.4.1 Using Command Procedures

Both ICCF and TSO/E provide the capability of storing frequently executed commands or lists of commands. In ICCF these stored commands are called Procedures or Macros. They are stored as an ICCF library member. In TSO/E they are called Command Lists (CLIST) or REXX execs.

Besides issuing TSO/E commands, CLISTs can perform more complex programming tasks. The CLIST language includes the programming tools needed to write extensive, structured applications. CLISTs can perform any number of complex tasks, from displaying a series of full-screen panels to managing programs written in other languages.

The CLIST language is an interpretive language. TSO/E also offers a second interpretive language, REXX. REXX is a general purpose, high-level language not unlike PL/I. REXX has the usual structured programming instructions and a number of useful built-in functions.

The main difference between ICCF Procedures and Macros is that macros are executed in the foreground as normal commands and may be invoked while in edit mode, whereas procedures are executed only in command mode.

Procedures require that execution of the procedure processor program be started in an interactive partition, which means that a macro is processed more quickly than a procedure. Another difference is that a procedure has more control over the flow and execution of commands than a macro.

In TSO/E, CLISTs and REXX programs are executable sequences of TSO/E commands, subcommands, and CLIST or REXX statements. The entire TSO/E command language is available to CLISTs and REXX programs.

To create a CLIST or REXX program, use the ISPF/PDF editor or the TSO/E EDIT command to put the commands, subcommands, and command procedure statements into a data set. The data set may be either sequential or partitioned. A sequential CLIST or REXX data set consists of only one program, while a partitioned data set may contain more than one program. When a PDS consists entirely of CLISTs, it is called a CLIST library. Detailed information on writing CLISTs can be found in TSO/E CLISTs.

7.5 Migrating from VSE/ICCF to MVS and TSO/E

As with any new system, TSO/E will require time to learn. Many of its functions are similar to those in ICCF but others are either entirely new, or differ enough that you will have to change your present methods in order to implement them.

In this section we will attempt to describe how you can begin the migration from VSE/ICCF to MVS TSO/E.

7.5.1 Converting ICCF Libraries

Although there are many methods for moving members from your existing ICCF libraries to data sets accessible to TSO/E, in this section we will discuss just two. The first method is to write an ICCF procedure that will create a tape file containing the JCL and data necessary to execute the MVS utility IEBUPDTE to create a new PDS containing the members from an ICCF library. The second method utilizes the ICCF utility DTSUTIL to punch ICCF library members to tape. A program would then need to be written to reformat this tape to a format that would be acceptable to the MVS utility IEBUPDTE. The advantage of the second

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IBM OS/390 manual Using Command Procedures, Migrating from VSE/ICCF to MVS and TSO/E, Converting Iccf Libraries
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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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