Provides a program translation and execution method which stores target routines (for execution by a target processor) corresponding to incompatible instructions, interruptions and authorizations of an incompatible program written for execution on another computer system built to a computer architecture incompatible with the architecture of the target processor's computer system. The disclosed process allows the target processor to emulate incompatible acts expected in the operation of an incompatible program when the target processor itself is incapable of performing the emulated acts. Each of the instructions, interruptions and authorizations found in the incompatible programs has one or more corresponding target routines, any of which may need to be preprocessed before it can precisely emulate the execution results required by the incompatible architecture. Target routines (corresponding to the incompatible instruction instances in an incompatible program being emulated) are accessed, patched where necessary, and executed by a target processor to enable the target processor to precisely obtain the execution results of the emulated incompatible program. Before preprocessing, each target routine may not be able to provide identical execution results as required by the incompatible architecture, and the preprocessing may patch one or more of its target instructions to enable the target routine to perform the identical emulation execution of the corresponding incompatible instruction. The patching and other modifications to a target routine are done by one or more preprocessing instructions stored in the target routine.