In a z/OS system, CICS provides a functional layer for managing transactions, with the operating system serving as the final interface with the computer hardware.

CICS Transaction Server (CICS TS) is the version of CICS that acts as an assistant to the z/OS operating system and functions as an administrative coordinator for other applications.

CICS TS operates as an intermediary between application programs, database managers, and access methods. It supports the system by efficiently handling complex tasks or transactions, allowing the system to focus on processing its regular non-transactional workload.

When an application program interacts with a terminal or any device, it does not communicate directly with it. Instead, the application program issues commands (CICS commands) to perform terminal input/output, file input/output, program control, and other functions. These commands communicate with the operating system's access methods, which then interact with the terminal or device, enabling the execution of the application program.

A z/OS system may have multiple instances of CICS (i.e., multiple systems) running simultaneously. Each instance of CICS starts as a separate address space within the z/OS environment.

A CICS region can be initiated by running a CICS region job in a batch environment. Since CICS operates as a batch job in the background of the operating system, two or more CICS regions can be active at the same time.

CICS Characteristics -

Below is the list of CICS Characteristics -

• Cost-effective.
• Instantaneous/immediate results.
• Multiple programs execution in parallel.
• Interact with the application program through maps.
• A pseudo conversation about reducing the CPU waiting time.
• Arithmetic operations are less effective.
• Effective when dealing with a small amount of data and less effective for the huge amount of data.

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