As fast and powerful commodity processors have been developed, it has become practical to emulate on platforms built using commodity processors the proprietary hardware systems of powerful older computers. High performance is typically a key requirement for a system even when built using emulation software. In a hardware design many special cases and conditions which may cause exceptions are detected by logic operating in parallel with the instruction execution. In software these checks can cost extra cycles of processor time during emulation of each instruction and be a significant detriment to performance. Avoiding some of these checks by relying upon the underlying hardware checks of the host system and then using a signal handler and special software to recover from these signals is a way to improve the performance and simplify the coding of the software emulation system.