CICS region

A region is an instance of CICS. It runs as a started task in its own address space, with its own set of defined programs, transactions, files and connections.

Sites run several rather than one large one. Separating them limits the damage when something goes wrong, allows different applications to be maintained on different schedules, and spreads load across a system or a sysplex.

A common arrangement splits the roles. Terminal-owning regions handle the users and their screens; application-owning regions run the business programs; file-owning regions manage access to the data. Requests are routed between them, so a user connected to one region runs a program in another that reads a file managed by a third. Done well, users are unaware of any of it, and a region can be recycled without anyone losing service.

Each region has a name, and knowing which one you are working in matters. The same transaction may exist in a development region and a production region with entirely different data behind it.