History of Television
I'm gonna use this and compare the differences according to the website. =)
Other companies not in the business of
broadcasting, including Paramount Pictures and the Zenith Corporation,
unveiled postwar plans to enter the field but were effectively blocked
by unfavorable governmental regulatory decisions that were lobbied for
by the broadcasting giants. In 1948, for example, the Federal Communications Commission
(FCC), a U.S. government agency that regulates broadcasting, instituted
a freeze on the issuance of new station licenses. In addition, the FCC
initially made only the 12 very high frequency (VHF) channels available
for broadcasting, prohibiting use of the 69 ultra high frequency (UHF)
channels, which created an artificial scarcity of station frequencies.
By the mid-1950s, the three leading broadcasting companies (NBC, CBS,
and ABC, which collectively became known as the Big Three), had
successfully secured American network television as their exclusive
domain. It was not until the mid-1980s that a fourth company, News Corporation, Ltd., owned by Australian-born executive Rupert Murdoch, broke their monopoly with the establishment of the Fox television network (see Fox Broadcasting Company). In the 1990s, two other communications giants, Paramount Pictures (a division of Viacom, Inc.) and Warner Bros. (a division of Time Warner Inc.), established networks in the United States.
Before cable television
(television signals transmitted by cable to paying subscribers only)
decisively ended channel scarcity in the 1980s, viewing choices had been
limited in most parts of the United States to the programming that the
three networks had developed.