CCYY format. A 4-digit-year format that uses two century digits (CC) to indicate the century and two year digits (YY) to indicate the year within the century. The CC representation is provided as either the actual century digits (for example, 18, 19, or 20) or as an encoded value (for example, as 00 to represent 19, 01 to represent 20 as in, 0095 represents the year 1995 and 0195 represents the year 2095.)

century. Although IBM recognizes that the 21st century begins at 0000 hrs, 2001-January-01, for purposes of this document, we are defining the 20thÐ21st century boundary to be between 2400 hrs, 1999-December-31 and 0000 hrs, 2000-January-1. This allows a discussion of the 21st century to include all dates with a 20yy format inclusive of the year 2000. Hence, the year 2100 is likewise relegated to the 22nd century.

century byte. The high order byte of a field used to contain the two high order digits of a 4-digit year. (For example, 19 in 1995, 20 in 2000 and 2001).

channel-to-channel (CTC). A method of connecting two computing devices.

character set. (1) An ordered set of unique representations called characters; for example, the 26 letters of the English alphabet, Boolean 0 and 1, the set of symbols in the Morse code, and the 128 ASCII characters. (2) A defined collection of characters. (3) All the valid characters for a programming language or for a computer system.

checkpoint data set. A data set that contains checkpoint records.

CICS. See Customer Information Control System.

CICS region. The CICS area of the computer system in which an application is running.

close. (1) A data manipulation function that ends the connection between a file and a program. Contrast with open. (2) To end the processing of a file.

cluster. In systems with VSAM, a named structure consisting of a group of related components; for example, a data component with its index component.

coexistence. The ability of different types of systems to support a program.

command language. A set of procedural operators with a related syntax, used to indicate the functions to be performed by an operating system. Synonymous with control language.

Common Programming Interface. Definitions of those application development languages and services that have, or are intended to have, implementations on and a high degree of commonality across the SAA

environments. One of the three SAA architectural areas.

communication region. In VSE, an area of the supervisor that is set aside for transfer of information within and between programs.

compilation. Translation of a source program into an executable program (an object program).

configuration file. A file that specifies the characteristics of a system or subsystem.

console. A part of a computer used for communication between the operator or maintenance engineer and the computer.

context editing. A method of editing a line without using line numbers. To refer to a particular line, all or part of the contents of that line is specified.

control block. A storage area used by a computer program to hold control information. Synonymous with control area.

control language (CL). The set of all commands with which a user requests functions. Synonym for command language. See job control language.

control program. (1) A computer program designed to schedule and to supervise the execution of programs of a computer system. (2) See VM/370 control program, resident control program, IMS/VS control program, VM/XA Migration Aid control program.

conversational. Pertaining to a program or a system that carries on a dialog with a terminal user, alternately accepting input and then responding to the input quickly enough for the user to maintain a train of thought. See also interactive.

conversion (VSE/MVS). A process that modifies VSE applications and data to meet MVS requirements.

copied member. A source text member that can be included in a flow of source data by means of COPY-like statements (COPY statements in Assembler, COBOL, or RPG II; %INCLUDE statements in PL/I; or any other alternate-COPY statements for nonstandard text inclusion).

cosmetic. Referring to a 2-digit-year date that is viewed by human eyes only, such as a print date on hardcopy output or a date on a selection panel. Because it is neither read nor further processed by a program you might be able to exclude its modification from your Year2000 work effort.

Customer Information Control System (CICS). An

IBM-licensed program that enables transactions entered at remote terminals to be processed concurrently by user-written application programs.

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IBM OS/390 manual Customer Information Control System CICS. An

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.