Unlike VSE, the operator does not manipulate elements within a job stream, nor is he given the opportunity to correct JCL errors. The processes are much more automated in OS/390 under the theory that the system will be better utilized and jobs run more efficiently without operator intervention.

4.2 High Level Similarities

A high level comparison of JCL in the VSE and OS/390 environments reveals many similar functions and purposes. A comparison of the mechanics in both environments reveals significant differences.

4.2.1 JCL Statement and Job Layout

VSE and MVS JCL are similar in the basic layout for the card images in that both use 80 Column Card Images, and both use // in columns one and two. Both operating systems also use the basic layout of a job with one or more steps per job as described in the philosophical discussion above.

4.2.1.1 Continuation Cards

Both use ASM-type continuation, but the basic layout differs in that:

VSE JCL statements are continued by placing a non-blank character in column 72, and JCL continuation cards must start in column 16 with blanks in columns 1 - 15.

MVS JCL statements are continued by placing a trailing comma in the

parameter field, and JCL continuation cards may start in any column from 4 to 16, with ²//² in columns 1 and 2, and a blank in column 3.

4.2.1.2 JOB Statement Starts a Job

In OS/390 there is only one JOB statement as opposed to the VSE POWER and VSE JOB statements. Much of the time the POWER job will equate to the MVS job.

4.2.1.3 EXEC Defines Job Step

The EXEC statement defines the job step in both VSE and MVS.

4.2.1.4 File Definitions

File definitions are required by both operating systems (TLBL, DLBL/EXTENT,

DD).

4.2.1.5 Imbedded JCL from Procedures and Libraries

Both operating systems support ªcanned JCLº and JCL procedures. In VSE, this is done through procedures (using PROC=procname in the EXEC card) and with the POWER * $$ SLI JECL statement (Source Library Inclusion). In OS/390, the same thing can be done with the PROC or INCLUDE JCL statements, respectively.

4.2.1.6 Nesting Procedures

Both operating systems allow for multiple levels of nested procedures. (MVS allows up to 15 levels while VSE allows up to 16 levels.)

72VSE to OS/390 Migration Workbook

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IBM OS/390 manual High Level Similarities, JCL Statement and Job Layout

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.