The SCB architecture defines a structure that supports the physical delivery of control information between multiple entities (requesting or serving functions) executing in a base system processor and one or more peer entities executing in an advanced function adapters. Some entities may act as clients (requesters) while others act as servers. The entities build the control block structure, and the control block delivery service is used by one entity in either a system unit or feature adapter to communicate control block information to another entity.
Based upon the information within a control block, data may also be communicated between the two entities. The communication of data is referred to as data delivery. The delivery of data is separate from the delivery of command and control information and the individual entities are responsible for requesting the transfer of the data.
In the simplest case, the control block delivery service may be viewed as supporting communication between client entities located in the system unit and server entities located in an adapter.