purpose of modifying or extending the functions of the IBM software product.

integer date. A count of days since a specified date. Various IBM software products have defined integer dates as follows:

Language/Product

Days Since

C

1969-Dec-31

COBOL

1600-Dec-31

Language Environment

1582-Oct-14

MVS/CICS/DB2

1899-Dec-31

integrity. The protection of systems, programs, and data from inadvertent or malicious destruction or alteration. See application integrity, data integrity, system integrity.

Interactive Computing and Control Facility (ICCF). An

IBM licensed program that makes the services of a VSE-controlled computing system available to authorized display station users.

interactive partition. In VSE, an area of virtual storage dynamically allocated for the purpose of processing a job that was submitted interactively from a terminal.

Interactive Problem Control System (IPCS). A component of VM that permits online problem management, interactive problem diagnosis, online debugging for disk-resident CP abend dumps, problem tracking, and problem reporting.

Interactive System Productivity Facility. An IBM licensed program that serves as a full-screen editor and dialogue manager. Used for writing application programs, it provides a means of generating standard screen panels and interactive dialogues between the application programmer and terminal user.

internal side. The creator or manipulator of a data entity. Used in this document to mean a module or routine that externalizes a 2- or 4-digit-year format entity to another module or routine.

Internet. A wide area network connecting thousands of disparate networks in industry, education, government, and research. The Internet network uses TCP/IP as the standard for transmitting information.

interoperability. The capability to communicate, execute programs, or transfer data among various functional units in a way that requires the user to have little or no knowledge of the unique characteristics of those units.

IOCDS. An input/output configuration data set (IOCDS) contains different configuration definitions for the selected processor. Only one IOCDS is used at a time. The IOCDS contains I/O configuration data on the files associated with the processor controller on

the host processor, as it is used by the channel subsystem. The CSS uses the configuration data to control I/O requests. The IOCDS is built from the production IODF.

IOCP. An IOCP (I/O configuration program) is the hardware utility that defines the hardware I/O configuration to the channel subsystem. For this definition IOCP retrieves information about the following: the channel paths in the processor complex, control units attached to the channel paths, and I/O devices assigned to the control unit.

IODF. An IODF (input/output definition file) is a VSAM linear data set that contains I/O definition information. This information includes processor I/O definitions (formerly specified by IOCP input streams) and operating system I/O definitions (formerly specified by MVSCP input streams). A single IODF can contain several processor and several operating system I/O definitions.

IPDS. Intelligent Printer Data Stream. An architected host-to-printer data stream that contains both data and controls defining how the data is to be presented.

IPL. Initial Program Load. (1) The initialization procedure that causes an operating system to commence operation. (2) The process by which a configuration image is loaded into storage, as at the beginning of a work day or after a system malfunction or as a means to access updated parts of the system.

(3)The process of loading system programs and preparing a system to run jobs.

J

JCL. Job Control Language. A sequence of commands used to identify a job to an operating system and to describe a jobs requirements.

JECL. Job Entry Control Language - also referred to as JES2 or JES3 control statements that are submitted with a jobs JCL.

JES. Job Entry Subsystem. A system facility for spooling, job queueing, and managing the scheduler work area.

job accounting. A function that collects information pertaining to how a job uses system resources.

job control. In VSE, a program called into storage to prepare each job or job step to be run. Some of its functions are to assign I/O devices to symbolic names, set switches for program use, log (or print) job control statements, and fetch the first phase of each job step.

job control language (JCL). A control language used to identify a job to an operating system and to describe the jobs requirements.

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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.