This paper describes the total design of Responsive Multithreaded (RMT) Processor, which is a system LSI that integrates almost all functions for parallel/distributed real-time control. Concretely, RMT Processor integrates an 8-way multithreaded processor (RMT Processing Unit) for real-time processing, real-time communication (Responsive Link II), computer peripherals (DDR SDRAM I/Fs, DMAC, PCI64, USB2.0, IEEE1394, etc.), and control peripherals (PWM Generators, Pulse Counters, etc.). RMT PU can execute eight prioritized threads simultaneously using the finegrained multithreading mechanism (RMT architecture). RMT PU introduces the priority of real-time systems into the processing unit, so that it can guarantee the execution of the prioritized threads according to the priority. Responsive Link II has a lot of unique features including separation of hard real-time communication (event link) and soft real-time communication (data link), the packet overtaking function with 256 level priority at each node, individual routing according to the type of the link and the packet priority, the packet accelerating/decelerating function by replacing the packet priority at each node, etc., so that Responsive Link II can realize real-time communication. RMT Processor can execute such tasks and communications prioritized by the real-time scheduler, overtaking and/or arbitrating them by hardware, to realize real-time communication and processing. As RMT Processor also realizes both high performance and low power, large scale parallel/distributed real-time systems can be designed by using RMT Processors.