A good opportunity to mention the Popek-Goldberg criteria. If Amdahl's machines had been able to efficiently trap on the use of the new instruction (and execute

A good opportunity to mention the Popek-Goldberg criteria. If Amdahl's machines had been able to efficiently trap on the use of the new instruction (and execute a workaround using their existing instruction set) they might have been OK. Depends what the instruction was used for. Popek-Goldberg discusses the case where you want to virtualise your hardware: instruction set design becomes really important.