An architectural framework that allows software applications and operating system code written for a given instruction set to migrate to different, higher performance architectures is described. The framework provides a hardware mechanism that enhances application performance while keeping the same program behavior from a user perspective. The framework is designed to accommodate program exceptions, self-modifying code, tracing, and debugging. Examples are given for IBM System/390 operating-system code and AIX utilities, showing the performance potential of the scheme using a very long instruction word (VLIW) machine as the high-performance target architecture. >