Abstract: A system and method for system and circuit level design modeling and simulation using the C++ programming language. Program interfaces in a behavior-less base class are provided to allow a circuit designer to model hardware blocks using user processes in C++. The present invention provides for the manipulation of software user processes that represent the behavior of circuit blocks. C++ is advantageous because it is a familiar language for many designers in the computer industry and therefore requires a smaller learning curve. The novel interface provides an efficient implementation of reactivity (waiting and watching) and concurrency (signals and processes) allowing designers to use C++ to model mixed hardware-software systems with a C++ compiler and a library of the present invention without the need of a complex event-driven run-time kernel, often required in other hardware description languages (HDLs).