A method of simulating a program. Compiled and interpretive techniques are combined into a just-in-time cached compiled technique. When an instruction of a program simulation is to be executed at run-time, a table of compiled instructions is accessed to determine whether compiled data for the instruction is stored in the table. If the compiled data is not therein, the instruction is compiled and stored in the table. The compiled data is returned to a simulator that is executing the program simulation. In another embodiment, before storing new information in the table, another table may be consulted to determine if the location to which the new information is to be stored is protected. If the table location is protected, the new information is not stored in the table. Rather, the new information is simply passed on to the simulator.