The data control block (DCB) provides the system with information about the characteristics and processing requirements of a data set to be read or written by the channel program. A DCB must be generated by a DCB macro instruction that includes parameters for EXCP. If you are not using appendages, a short DCB is constructed. Such a DCB does not support reduced error recovery. You specify the address of the DCB in the IOB. See Data Control Block (DCB) Fields.