[en] The process control industry has experienced a major transition in control systems technology based on microprocessor digital control. The microprocessor technology coupled with similar advancements in communications, software compilers, advanced software design tools, and advanced control theory has resulted in a wide range system architectures and functional distributions available. This transition has resulted in requiring new methods of developing, designing and implementing control systems. Also, these methods have provided a marked improvement in reliability and stability of the new control systems. Honeywell's ten years of experience in microprocessor based control is discussed and this experience in microprocessor based control to the nuclear industry effort is related. The recent TDC 3000 development, the design considerations, and implementation experience are described. Based on this experience, a summary of key design criteria for specification and evaluation of distributed digital control systems is discussed