> Instructions that have completed execution and have not yet been committed are analogous to cars that have gone through our hypothetical repair shop and are waiting for their owners to pick them up. However, all analogies break down, and the world of automobiles does not have a natural counterpart for the notion of speculative execution. That notion corresponds roughly to situations in which people are led to believe that their cars need a new piece of equipment, but they suddenly change their mind once they see the price tag, and they insist on having the equipment removed even after it has been partially or completely installed.