Alpha, Beta, and Unlimited are often considered to be the same set. Well, that's because they basically are. Beta was just the second printing of Alpha, and Unlimited was just a reprinting of Beta. This happened because Wizards of the Coast had no idea in how popular Magic would be when they released it. They originally intended to release a follow-up set shortly after the initial release. But the public demanded more cards before an expansion would be ready. So, Wizards gave them Unlimited.