The eye of round comes from the hind quarter of a cow. This area is a well used muscle and doesn't have a lot a fat,therefore, making it a tough, chewy piece of meat if cooked at the wrong heat.
The eye round roast comes from the back hip section of the cow. This makes the meat contain a lot of flavor and because ot the exercise this area of the cow gets, it is a very tender cut of meat. Round steak and bottom round roast come from the same section.