Well those two are about the same, but there are some differences.
First the beginnings, Cheddar (in England) was hand pressed, cut and stacked on a table or sorts to let the whey run off and the Monterey Friars that made the cheese called Jack cheese because they used two wood paddles held together by leather straps (thus the jack) to press the whey from the curds thus making the cheese faster.
However there are a few other differences, the jack cheese is made from whole milk, while in cheddar the curds are "cheddared" or cut then into slabs set on the table to drain also cheddar is made from skim milk as the cream was more important than to make into the cheese. The rest is actually about the same.
I think that to this day Jack cheese is still pressed and quick to make from pasteurized whole milk, while Cheddar is still cut and stacked to let the whey run off with some but not all made from skim milk
From Kraft foods, WHY WOULDN'T CHEESE BE VEGETARIAN?!?
A crucial ingredient in the production of most commercial cheeses is an enzyme that comes from the lining of the stomach of calves, called rennet. Sometimes an enzyme from pigs is also used. Obviously, this is of concern to vegetarians, since these are products obtained from slaughtered animals. According to the American Heritage Dictionary, `rennet' is actually the lining of the fourth stomach of calves and other young ruminants, but this term is also used to refer to the enzyme that is extracted from the stomach lining for use in making cheese. `Rennin' is another word for this enzyme, although it is less commonly used. These enzymes are important because they are the ingredients that cause milk to coagulate and eventually become cheese. Following is a very informative letter we received from the Consumer Service Department of Kraft General Foods, Inc., which clearly describes the role animal enzymes play in the production of cheese. We are grateful to Ellen Schwarzbach of Kraft for taking the time to give us such a thorough explanation.
Why me? why now? well as cheese is one of my more favorite food groups and now I shouldn't eat it very much at all anymore, that's why