* ABC: The American Broadcasting Company had 14 affiliates in 1953, when its present corporate structure was established. By the 1970s, it had become an equal player with CBS and NBC. In 1985, it was acquired by Capital Cities Communications.
* CBS: The Columbia Broadcasting System (it became CBS Inc.) began in 1927 as a radio broadcaster. Sale rumors have dogged it ever since the 1994 failure of a merger deal with cable system QVC.
* NBC: The National Broadcasting Company, a subsidiary of RCA, began in 1926. The General Electric Corporation bought RCA in 1986.