In a digital computer, the circuits that effect (a) the selection and retrieval of instructions from storage or from outside the computer in proper sequence, (b) the interpretation of each of the coded instructions in the computer program, (c) the development and application of proper signals to the arithmetic-logic units (ALUs) in accordance with the interpretation, and (d) the execution of instructions by the arithmetic-logic units, the storage units, and the input-output units. Note 1: Several control units may be subordinated to a central or main control unit. The control units and the arithmetic-logic units form the main part of the central processing unit. Note 2: The computer control unit circuits may be mounted on a single chip. See also  arithmetic-logic unit,  central processing unit,  circuit,  chip,  computer,  computer program,  digital computer,  effect,  execute,  input-output unit,  instruction,  interpret,  retrieval,  storage,  storage unit.