Subsystem connections

The connection between an IMS application program and the external subsystem is called a thread. Application threads are two-way communication paths between IMS application programs and external subsystem resources.

An application program can have more than one thread since it can access more than one external subsystem in one execution. However, access to multiple subsystems of the same type (multiple instances of the same subsystem type) while supported by IMS, might not be supported by the external subsystem product.