multivolume file. A file contained on more than one storage medium.

N

NetView DM. IBM NetView Distribution Manager.

network definition. In VTAM, the process of defining the identities and characteristics of each node in the network and the arrangement of the nodes in that system.

network management. The process of planning, organizing, and controlling a communications-oriented system.

network resource. In ACF/VTAM, a network component such as a local network control program, SDLC data link, or peripheral node. In multiple-domain networking, cross-domain resource managers (CDRMs) and logical units (LUs) in other domains are also network resources.

network topology. The schematic arrangement of the links and nodes of a network.

node. An endpoint of a link or a junction common to two or more links in a network. Nodes can be processors, communication controllers, cluster controllers, or terminals. Nodes can vary in routing and other functional capabilities. (6) In VTAM, a point in a network defined by a symbolic name. See major node, minor node.

nonstandard labels. Labels that do not conform to American National Standard or IBM standard label conventions.

O

Object Access Method (OAM). In the IBM ImagePlus system, a program that provides object storage, object retrieval, and object storage hierarchy management. The Object Access Method isolates applications from storage devices, storage management, and storage device hierarchy management.

object code. Output from a compiler or assembler which is itself executable machine code or is suitable for processing to produce executable machine code.

object module. (1) All or part of an object program sufficiently complete for linking. Assemblers and compilers usually produce object modules. (2) A set of instructions in machine language produced by a compiler from a source program.

object program. (1) A target program suitable for execution. An object program may or may not require linking. (2) Contrast with source program.

open. The function that connects a file to a program for processing.

operating system (OS). Software that controls the execution of programs and that may provide services such as resource allocation, scheduling, input/output control, and data management. Although operating systems are predominantly software, partial hardware implementations are possible.

operator console. A display console used for communication between the operator and the system, used primarily to specify information concerning application programs and I/O operations and to monitor system operation.

option. A specification in a statement that may be used to influence the execution of the statement.

Ordinal Day of Year. See Julian Date

output area. An area of storage reserved for output.

output class. In OS/390, one of up to 36 different categories, defined at an installation, to which output data produced during a job step can be assigned. When an output writer is started, it can be directed to process from one to eight different output data classes.

output data set. A data set that contains data that is to be printed or displayed.

output file. (1) A file that has been opened in order to allow records to be written. (2) Contrast with input file.

overlay structure. A graphic representation showing the relationships of segments of an overlay program and how the segments are arranged to use the same main storage area at different times.

P

parameter list. A list of values that provides a means of associating addressability of data defined in a called program with data in the calling program. It contains parameter names and the order in which they are to be associated in the calling and called program.

partition. In VSE, a division of the virtual address area that is available for program execution.

partitioned data set (PDS). A data set in direct access storage that is divided into partitions, called members, each of which can contain a program, part of a program, or data. Synonymous with program library.

Pascal. A high-level, general-purpose programming language, related to ALGOL. Programs written in Pascal are block structured, consisting of independent

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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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