IMS consists of three components:

• the Transaction Manager (TM) component
• the Database Manager (DB) component, and
• a set of system services that provide common services to the other two components.

The IMS Transaction Manager provides you with access to applications running under IMS. You can be at a terminal or a workstation, or other application programs, either on the same OS/390 system, on other OS/390 systems, or on other non-OS/390 platforms. The IMS database manager component supports databases using the IMS hierarchical database model. It provides access to these databases from applications running under the IMS Transaction Manager. IMS has control regions and dependent regions (for example, message processing region, batch message processing (BMP) region, etc.).

The IMS control region provides the central point for an IMS subsystem. It provides the interface to the SNA network for the Transaction Manager functions and the Transaction Manager OTMA interface for access to non-SNA networks. It provides the interface to OS/390 for the operation of the IMS subsystem. It controls and dispatches the application programs running in the various dependent regions. The IMS MPP region is used to process messages input to the IMS Transaction Manager component (that is, online programs). The address space does not automatically load an application program, but waits until work becomes available. The BMP region consists of two sub-types, Message Driven BMP (also called transaction oriented BMP) which reads and processes messages from the IMS message queue, and Non-message BMP (batch oriented) which do not process IMS messages but have access to the IMS DB.