There are currently 30 undergraduate residence halls at the University of Notre Dame. Each residence hall is single sex, with 16 all-male residence halls and 15 all-female residence halls. The university also hosts Old College, an undergraduate residence for students preparing for the priesthood.Notre Dame has an undergraduate hall system which blends the residential college system and the house system. All first year students are placed in one of the 30 halls upon enrollment, and students rarely switch halls. Each hall has its own spirit, tradition, mascot, sport teams, events, dances and reputation. Approximately 80% of undergraduate students live on campus, and often a student lives in the same dorm for the entirety of their undergraduate career. A huge segment of student life happens through residence halls and students develop a particular attachment to their undergraduate hall. Each residence hall is directed by with one Rector with the assistance of two Assistant Rectors and a variable number of Resident Assistants (from 4 to 9). Every residence hall has a chapel where Mass is held, fields a variety of intramural sports teams, elects one senator to represent the dorm in Student Government, and elects co-presidents which work through the Hall Presidents Council (HPC) student organization. Interhall football between Notre Dame male dorms is the only interhall tackle football which has remained at any US university.With the exception of Carroll Hall, the residence halls are split among five main segments of the campus: Main (God) Quad, South Quad, North Quad, Mod Quad and West Quad. All first-year students are not only guaranteed on-campus housing, but are required to reside on campus for at least one semester. Many of the halls were inserted in 1973 on the National Register of Historic Places.