CICS

“Customer Information Control System” is what CICS® stands for. It serves as the z/OS® operating system’s general-purpose transaction processing subsystem. While many other customers request to execute the same applications using the same files and programs, CICS offers services for executing an application online upon request.

CICS controls resource allocation, data integrity, and execution priority while responding quickly. Users are authorized by CICS, which distributes resources (such as actual storage and processing cycles) and forwards database queries from the program to the proper database management (such as DB2®). We may claim that CICS behaves similarly to the z/OS operating system and carries out many of the same tasks.

A CICS application is a group of connected applications that work together to complete a business task, like processing a travel request or creating a paycheck for a corporation. Applications under CICS control access programs and files through CICS services and interfaces.

Traditionally, CICS applications are launched by submitting a transaction request. Running one or more application programs that implement the necessary function constitutes the transaction’s execution. CICS application programs are occasionally referred to in CICS documentation as “programs,” Sometimes, the term “transaction” is used to denote the processing carried out by the application programs.

Enterprise JavaTM Beans can also be used as CICS applications. 

Functions of CICS

The following are the primary tasks carried out by CICS in an application

• CICS handles requests from several program users simultaneously.
• Even if numerous users are working on the CICS system, the user still gets the impression that he is the only one.
• CICS provides access to data files so that they can be read or updated in an application.

Features of CICS

The following are CICS’s Features

• CICS manages its processor storage, has a task manager that supervises the execution of many programs, and offers its file management features, making it an operating system unto itself.
• The batch operating system offers an online environment thanks to CICS. Jobs submitted are instantly carried out.
• CICS is a standardized interface for transaction processing.
• As CICS runs as a batch task in the operating system at the back end, it is feasible to have two or more CICS regions active simultaneously.
• CICS functions as an operating system by itself. Its responsibility is to offer a setting for the online execution of application programs. CICS only utilizes one address space, region, or partition. CICS manages the program schedule for those that use it. Using the command PREFIX CICS*, we may examine CICS in the spool where it runs as a batch job. The five main services offered by CICS are listed below. Together, these services complete a task.

CICS Environment

The services that we will go over in-depth, step by step, are as follows

• Computer Services
• Services for Data Communication
• Services for Handling Data
• Services for Application Programming
• Monitoring Services

The following control functions are maintained by CICS to manage the allocation or de-allocation of resources within the system

• Task Control offers capabilities for multitasking and task scheduling. It handles maintaining the state of every CICS task. The processor’s time is divided across running CICS tasks by Task Control. We refer to this as multitasking. CICS prioritizes the most critical job response time.
• Program Control controls how application programs are loaded and released. It is vital to link a task with the relevant application software as soon as it starts. Despite the fact that multiple tasks may require the same application program, CICS only loads one instance of the code into memory. This code allows for independent task threading, enabling several users to conduct transactions simultaneously while using the same application program’s physical copy.
• Storage Control controls the acquisition and release of primary storage. Dynamic storage is acquired, managed, and released through storage control. Input/output zones, programs, etc., use dynamic storage.

Interval Control provides timer services.

• Services for Data Communication
• To handle data communication requests from application programs, Data Communication Services interface with telecommunication access methods like BTAM, VTAM, and TCAM.
• Using Basic Mapping Support, CICS relieves application programs from the task of resolving terminal hardware difficulties (BMS).
• Through Multi-Region Operation (MRO), multiple CICS regions within the same system can communicate with one another.
• Inter System Communication (ISC) is a feature of CICS that enables the communication between a CICS area on one system and a CICS region on another system.

Services for Handling Data

• BDAM, VSAM, and other data access mechanisms are interfaced with data handling services.
• Data handling requests from application programs are made easier by CICS. Application programmers can use a set of instructions provided by CICS to manage data set and database access, as well as associated processes.
• Data Handling Services assist in processing database queries from application programs by integrating with database access techniques like IMS/DB, DB2, etc.
• By controlling simultaneous record updates, protecting data when tasks ABEND, and protecting data during system failures, CICS makes it easier to manage data integrity.

Services for Application Programming

Applications are interfaced with using application programming services. Features offered by the CICS application programming services include command-level translation, CEDF (the debug facility), and CECI (the command interpreter facility). In the following modules, we’ll go into further detail.

Monitoring Services

Monitoring services for various events monitor the CICS address space. It offers numerous statistical data points that can be utilized to fine-tune the system.