A method and system for selecting the architecture level to which a processor appears to conform within a computing environment when executing specific logical partitions or programs and performing migration among different levels of processor architecture. The method utilizes a “processor compatibility register” (PCR) that controls the level of the architecture that the processor appears to support. In one embodiment, the PCR is accessible only to super-privileged software. The super-privileged software sets bits in the PCR that specify the architecture level that the processor is to appear to support so that when the program runs on the processor, the processor behaves in accordance with the architecture level for which the program was designed.