GRS. global resource serialization. A component of MVS/ESA SP used for sharing system resources and for converting DASD reserve volumes to data set enqueues.

Guest Operating System (GOS). A second operating system that runs on the primary operating system. An example the second operating system is VSE and/or OS/390 and/or TPF etc. running on VM/ESA. In this example VSE, OS/390, TPF, etc. are referred to as a second level system or a VSE guest, OS/390 guest, TPF guest and so on.

Guest Support. A set of functions and services available on the VM/ESA product that allow other operating systems such as OS/390, VSE, TPF, VM, and others to run on the primary host VM/ESA system. This is also sometimes referred to as ²using VM as a hypervisor for running other operating systems².

H

hardcopy log. In systems with multiple console support or a graphic console, a permanent record of system activity.

HCD. Hardware Configuration Definition. An interactive interface in MVS and OS/390 that enables an installation to define hardware configurations from a single point of control.

HFS data set. hierarchical file system data set. A data set that contains a POSIX-compliant hierarchical file system, which is a collection of files and directories organized in a hierarchical structure, that can be accessed using the OpenEdition MVS facilities.

high-level language (HLL). A programming language whose concepts and structures are convenient for human reasoning; for example, Pascal. High-level languages are independent of the structures of computers and operating systems.

HMC . Hardware Management Console A console used to monitor and control hardware such as the System/390 microprocessors.

host system. (1) A data processing system used to prepare programs and operating environments for use on another computer or controller. (2) The data processing system to which a network is connected and with which the system can communicate.

I

I/O area. An area of storage that contains data which is used in input/output operations; for example, an I/O buffer.

ICCF. See Interactive Computing Control Facility.

ICKDSF. See Device Support Facilities.

IDCAMS. Utility program name for Access Method Services (AMS).

IMS/VS . See Information Management

System/Virtual Storage.

Information Management System/Virtual Storage

(IMS/VS). A data base/data communication (DB/DC) system capable of managing complex data bases and networks

information processing. The systematic performance of operations on information in conjunction with a computer system to obtain, manipulate, duplicate, exchange, or communicate its meaning; for example, file management, word processing, document interchange, facsimile, videotext.

Information/Management. A feature of the Information/System licensed program that provides interactive systems management applications for problem, change, and configuration management.

Information/System. In the NetView program, an interactive retrieval program with related utilities designed to provide systems programmers with keyword access to selected technical information contained in either of its companion products, Information/MVS or Information/VM-VSE.

initiator/terminator. The job scheduler function that selects jobs and job steps to be executed, allocates input/output devices for them, places them under task control, and at completion of the job, supplies control information for writing job output on a system output unit.

input data set. A data set that contains data to be

processed.

input file. A file that has been opened in order to allow records to be read. Contrast with output file.

input/output (I/O). Pertaining to a device, process, or channel involved in data input, data output, or both.

installation. (1) In system development, preparing and placing a functional unit in position for use. (2) A particular computing system, including the work it does and the people who manage it, operate it, apply it to problems, service it, and use the results it produces.

installation exit. The means specifically described in an IBM software product¢s documentation by which an IBM software product may be modified by a customer¢s system programmers to change or extend the functions of the IBM software product. Such modifications consist of exit routines written to replace one or more existing modules of an IBM software product, or to add one or more modules or subroutines to an IBM software product, for the

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IBM OS/390 manual Information Management System/Virtual Storage

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.