Hard Cheese Question

Question

Can you explain what makes cheese "hard"? I saw this (see below) on the Star-K site FAQ, that Swiss, Cheddar, Muenster, and Mozzarella are not hard cheeses. Are you you familiar different halachic opinions on this? Thanks in Advance. "Q. What are the cheeses that are considered "hard cheeses" for which one has to wait six hours before eating meat? Are cottage and cream cheese considered hard cheeses? What if the hard cheese is cooked? A. Hard cheese is cheese that has been aged so that it no longer can be sliced. Parmesian cheese is considered hard if it has been aged for six months. Romano may also be a hard cheese (but is not readily available as kosher). Swiss, Cheddar, Muenster, and Mozzarella are not hard cheeses. Cottage and cream cheese are certainly not hard cheeses either. If a hard cheese is cooked, it does not lose its status as a hard cheese."