Although sometimes called "red rat snakes," corn snakes are a different species than rat snakes, though they belong to the same genus. King snakes and milk snakes are the same way - same genus, different species.
As far as care, black, yellow, Everglades and gray rat snakes generally grow bigger than corn snakes. Most captive bred corns average 3-1/2 feet. The ratsnakes I mentioned above are typically four or more feet in length as adults, sometimes reaching 6 to 7 feet. There are very few 6 foot corn snakes.
The above-mentioned rat snakes all have climbing tendencies and are well known to include birds in their diet. In the wild birds probably make up a larger part of the diet of the above-metioned rat snakes than they do in corn snakes. Either way, rodents are a complete diet for corns and rats alike.
As far as pets, rat snakes can make great display animals, due to the fact that they like to climb. I have found corn snakes to be far more tame than rat snakes, which have a tendency to bite if caught off guard (although every snake has its own personality).
Below is a pic of a black rat snake I found in Hocking Hills Ohio in May is this year.
Tim

Third Eye