Abstract: A system for simulation of target electronic systems combining interacting elements of hardware and executing software, in part by physical emulation means and in part by abstract software simulation. A processor emulator is coupled to a hardware simulator by a communications link. The processor emulator provides the functionality of the target microprocessor while the hardware simulator simulates additional target circuitry. The processor emulator is coupled to a memory containing the target program. Most computer instructions in the target program do not require interaction with the target circuitry simulated on the hardware simulator. However, when a computer instructions requires the interaction of the target microprocessor and the target circuitry, a communications link control the communication between the target microprocessor and the target circuitry. The various components of the system can be coupled together via a conventional computer network.