Cycle simulators, in-circuit emulators, and hardware accelerators have made it possible to rapidly model the functionality of large digital designs. But these techniques provide limited visibility of internal design nodes, making debugging hard. Simulators run slowly when all nodes are traced. Emulators provide full visibility only with limited depth, or with greatly reduced speed. This paper discusses software techniques for increasing design visibility while reducing tracing overhead in simulation, and achieving 100% visibility in emulation without reducing speed or compromising depth.