The IMS control region is a z/OS address space that can be initiated through a z/OS START command or by submitting job control language (JCL)⁸ job.

The IMS control region provides the central point of control for an IMS subsystem. The IMS control region:

• Provides the interface to z/OS for the operation of the IMS subsystem.
• Controls, schedules, and dispatches the application programs that are running in separate regions, called dependent regions.
• Provides the interface to the SNA network for IMS TM functions.
• Provides the OTMA interface for access to non-SNA networks.
• Provides the ODBA interface for DB2 UDB for z/OS stored procedures and other z/OS application programs.

The IMS control region also provides all logging, restart, and recovery functions for the IMS subsystems. The terminals, message queues, and logs are all attached to this region. Fast Path (one of the IMS database types) database data sets are also allocated by the IMS control region.

A z/OS type-2 supervisor call (SVC) routine is used for switching control information, message and database data between the control region, all other regions, and back.

Four different types of IMS control regions can be defined using the IMS system definition process. You choose the one you want depending on which IMS functions you want. The four types of IMS control regions support the four IMS environments. These environments are discussed in more detail in IMS Environments.