Magnum, P.I. is a American tv show starring Tom Selleck as Thomas Magnum, a private eye living on Oahu, Hawaii. The show ran in the CBS television system that was American from 1980 to 1988 from first-run broadcast.According to the Nielsen ratings, Magnum, P.I. always ranked in the top twenty U.S. tv programs throughout the first five years that the show was originally broadcast in the USA. Originally appearing at a prime time American network timeslot of 8 Eastern on Thursdays, Magnum, P.I. was one of those highest-rated shows on U.S. tv.