Subdivisions
Subdivisions in Division I exist only in football. In all other sports, all Division I conferences are equivalent. The subdivisions were recently given names to reflect the differing levels of football play in them. Additionally, some sports, most notably ice hockey and men's volleyball, have completely different conference structures that operate outside of the normal NCAA sports conference structure.
The method by which the NCAA determines whether a school is Bowl or Championship subdivision is first by attendance numbers and then by scholarships.
For attendance reporting methods, the NCAA allows schools to report either total tickets sold or the number of persons in attendance at the games. They require a minimum average of 15,000 people in attendance every other year. These numbers get posted to the NCAA statistics website for football each year. With the new rules starting in the 2006 season, the number of Bowl Subdivision schools could drop in the future if those schools are not able to pull in enough fans into the games. Additionally, 8 schools in the Championship subdivision had enough attendance to be moved up in 2005 (although they would need to either compete as independents or join a conference in order to do so).
Read more about this topic: Division I (NCAA)