Symbolic simulation is the simulation of the execution of a computer system on an incompletely defined, or symbolic, state. This process results in a set of expressions that define the final machine state symbolically in terms of the initial machine state. We describe our use of symbolic simulation in conjunction with the development of the JEM1, the world’s first Java processor. We demonstrate that symbolic simulation can be used to detect microcode design errors and that it can be integrated into our current design process.