During the course of their 18-year career, Nine Inch Nails have only produced four proper, full-length albums:
-1989's Halo Two "Pretty Hate Machine"
-1994's Halo Eight "The Downward Spiral"
-1999's Halo Fourteen "The Fragile"
-2005's Halo Nineteen "With Teeth".
There is about five years between each major release.