Abstract: A plurality of processing elements independently operate in parallel on separate streams of data but in response to common instructions. In order to selectively and individually enable each processing element, a control register stage is provided for each. Each register may be controlled, as between its enabling and disabling states with respect to execution of a common instruction, by the results of a test performed by its associated processor in response to a prior instruction and by the complement of the test results. The system is especially adapted to support flow of control operators, such as IF/THEN constructs, IF/THEN/ELSE constructs and WHILE/DO loop constructs.