The question of who would win in a fight between Muhammad Ali and Mike Tyson is a classic one. Unfortunately, the world will never know since they came from two different generations of boxers. Both of them stood so far ahead of the other fighters from their era, they are still considered two of the greatest that ever lived.
Without using a computer simulator it's still possible to try and find an answer. Tysons trainer, the boxing scholar Cus D' Amato had another heavy weight champion from Ali's era. His name was Floyd Patterson. Ali and Patterson fought twice, with Ali winning both fights. The video I posted is of their first match in the 1965. Their rematch was in 1972.
Floyd Patterson was the first heavyweight boxer to ever win the title twice. If he beat Ali he would have been the first to win it three times.
When you watch the video you can immediately see that Patterson is not Mike Tyson. They say he had an injury during the fight, but I can spot errors in his style that have nothing to do with being injured. There are similarities between Patterson and Tyson. Patterson was a small heavyweight. His peakaboo style was very similar, since they were both trained by Cus. However, Patterson was clearly not the human tornado that Tyson was. He lacked the same punching power, and his footwork leaves something to be desired.
I think if Patterson had the same physical attributes of Mike Tyson his boxing style would have allowed him to get inside Ali. Once in close range his punching power would have ended it. Ali was good, and people still try to copy his style. But I don't believe his trademark footwork and hand speed would have saved him. Tyson had a crushing left hook that came out of no where. Patterson's left hook was telegraphed and didn't have the same kind of power. It worked on all his opponents, except for Ali.
It goes without saying that Ali didn't knock out Patterson in both of their fights. The second fight was stopped in the eighth round due to a cut on Patterson's eye. But, if it wasn't stopped I bet it would have gone the distance. That just proves he wouldn't have been able to KO Tyson. Mike Tyson had all the advantages of Floyd Patterson, and none of his weaknesses. It would have been too much for Muhammad Ali.