Enterprise CICS deployments run many regions that work together: a CICSplex is a set of CICS regions managed as one, often with Multi-Region Operation (MRO) so that regions can route transactions and share workload. CICSPlex SM (CICSPlex System Manager) provides a single point of control for monitoring and managing these regions. When CICS runs in a Parallel Sysplex, regions on different z/OS images can cooperate and share data. This page introduces CICSplex, MRO, region roles (TOR, AOR, FOR), CICSPlex SM, and how they fit into enterprise CICS architecture.
Imagine a big company with many offices (regions). Each office can do some of the work, but they talk to each other: one office answers the phone (terminals), another does the calculations (applications), another keeps the files (data). The boss has one dashboard (CICSPlex SM) to see all offices and move work between them. When one office is busy, work can go to another. That way the company can handle lots of customers and stay available even if one office has a problem. CICS enterprise is like that: many regions, each with a role, working together and managed together.
A CICSplex is a group of CICS regions that are administered and operated as a single unit. The regions can be on one or more z/OS images (e.g. in a Parallel Sysplex). From an operational and management perspective, the CICSplex is the scope of control: you define and monitor resources, route transactions, and manage workload across the regions in the CICSplex. CICSPlex SM typically provides the management interface for a CICSplex, so that operators and system programmers see one logical CICS system even though it is implemented as many regions.
MRO allows CICS regions to communicate and to distribute work. Regions connect via interregion communication (IRC); one region can send a request to another (e.g. to run a program or access a file in a different region). In a classic MRO design, regions are assigned roles: TOR (Terminal Owning Region) owns the terminal connections and receives user input; it may run some transactions locally or route them to an AOR (Application Owning Region). The AOR runs the application program and may in turn call a FOR (File Owning Region) for file I/O. This separation allows you to scale terminals, application capacity, and data access independently and to isolate failures.
| Role | Purpose |
|---|---|
| TOR (Terminal Owning Region) | Owns terminals and sessions; handles screen I/O; routes transactions to AORs |
| AOR (Application Owning Region) | Runs application programs and business logic |
| FOR (File Owning Region) | Owns files and datasets; performs file I/O |
| ACR (Auxiliary Control Region) | Monitoring, logging, system management |
CICSPlex SM (CICSPlex System Manager) is the system management component for CICS. It provides a single point from which to manage and monitor multiple CICS regions and CICSplexes. Functions include real-time monitoring (transaction rates, response times, resource usage), workload management and dynamic transaction routing, resource definition and deployment, and operational automation. So in an enterprise setup, CICSPlex SM is the "control tower" for CICS, even though the actual transaction processing runs in the individual regions.
Parallel Sysplex is the z/OS clustering technology that allows multiple z/OS images to work as one system, with shared data (e.g. via coupling facility) and coordinated failure recovery. CICS regions in a CICSplex can run on different images in a Sysplex. They use MRO (and related protocols) to communicate across images. This gives high availability: if one image fails, CICS regions on other images can continue, and workload can be shifted. Enterprise CICS installations often run a CICSplex inside a Sysplex to achieve scalability and continuous availability.
1. What is a CICSplex?
2. Which region type owns terminal connections and routes work to application regions?
3. What does CICSPlex SM provide?