region in register 1. The first eight bytes of the communication region is the date in the form MM/DD//YY (month/day/year) or DD/MM/YY (day/month/year).

Job Name

The VSE communication region contains the job name that appears in the JOB control statement. This name remains for the duration of the job and can be used in a job by using the COMRG macro to get the address of the communication region and a displacement of 24 to get the job name.

User Program Communication Bytes

In VSE, the problem program can modify the communication region. You can use bytes 12 to 22 to communicate results of one job step to succeeding job steps.

MVS can transfer a return code at job completion time. The initiator/terminator, via JCL (the COND parameter), examines the code but does not pass it to the next job step. You can communicate data from one job step to the next in the same job by passing a data set from one step to another or by including a user-written SVC routine.

UPSI (User Program Switch Indicators)

UPSI consists of one byte set to binary zero when the JOB control statement is encountered. You can modify the VSE UPSI byte in two ways.

1.Through an UPSI job control statement.

2.By the problem program.

In MVS, the PARM field of the EXEC statement or a control card can be used to pass information from the JCL to the assembler program.

Problem Program Area Addresses

The VSE communication region has five fields that relate to the problem program area:

1.The address of the first byte of background problem program area.

2.The address of the uppermost byte of problem program area.

3.The address of the uppermost byte of current problem program phase.

4.The address of the uppermost byte used in loading any phase of the problem program.

5.Length of the problem program label area.

This information is generally used for two main reasons by VSE programs:

1.To dynamically expand a phase at execution time into available storage for maximum program efficiency.

2.To dynamically load phases into available storage locations and avoid overlays where possible.

Although MVS does not provide similar fields, both techniques of dynamic virtual storage utilization are available to you: an explicit request for virtual storage, and an implicit request. Using virtual storage directly by the requesting module

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IBM OS/390 Job Name, User Program Communication Bytes, Upsi User Program Switch Indicators, Problem Program Area Addresses
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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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