Historically, analog and hybrid computer systems have provided effective real-time solutions for the simulation of large dynamic systems. In the mid 1970s, ADI concluded that these systems were no longer adequate to meet the demands of larger, more complex models and the demand for greater simulation accuracy. The decision was to design an all-digital system to satisfy these growing requirements (see Gilbert and Howe, (1978)). This all-digital approach was called the SYSTEM 10. The SYSTEM 10 has been effective in solving time-critical simulation problems and in replacing the previous approach of utilizing hybrid computers. Recent advances in 100 K emitter coupled logic (ECL) now make it possible to support a new generation of equipment that expands modeling capabilities to serve simulation needs. The hardware and software concepts of this system, called the SYSTEM 100, are the subject of this paper.