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The original inventors of radio, such as Nikola Tesla and Guglielmo Marconi, expected it to be used for one-on-one wireless communication tasks where telephones and telegraphs could not be used because of the problems involved in stringing copper wires from one point to another, such as in ship-to-shore communications. Those inventors had no expectations whatever that radio would become a major mass media entertainment and information medium earning many millions of dollars in revenues annually through radio advertising commercials or sponsorship. These latter uses were brought about after 1920 by business entrepreneurs such as David Sarnoff, who created the National Broadcasting Company (NBC), and William S. Paley, who built Columbia Broadcasting System (CBS). These broadcasting (as opposed to narrowcasting) business organizations began to be called network affiliates, because they consisted of loose chains of individual stations located in various cities, all transmitting the standard overall-system supplied fare, often at synchronized agreed-upon times. Some of these radio network stations were owned and operated by the networks, while others were independent radio owned by entrepreneurs allied with the respective networks. By selling blocks of time to advertisers, the medium was able to quickly become profitable and offer its products to listeners for free, provided they invested in a radio receiver set.
The new medium had grown rapidly through the 1920s, vastly increasing both the size of its audience and its profits. In those early days, it was customary for a corporation to sponsor an entire half-hour radio program, placing its commercials at the beginning and the end. This is in contrast to the pattern which developed late in the 20th century in both television and radio, where small slices of time were sold to many sponsors and no corporation claimed or wanted sponsorship of the entire show, except in rare cases. These later commercials also filled a much larger portion of the total program time than they had in the earlier days.
In the early radio age, content typically included a balance of comedy, drama, news, music and sports reporting. Variety radio programs included the most famous Hollywood talent of the day. During the 1920s, radio focused on musical entertainment, the Grand Ole Opry, has been focused on broadcasting country music since it began in 1925. Radio soap operas began in the U.S. in 1930 with Painted Dreams. Laurdagsbarnetimen, a Norwegian children's show, with its premiere in 1924, is still being broadcast weekly, which makes it the longest running radio show in the world.
In the early 1950s, television programming eroded the popularity of radio comedy, drama and variety shows. By the late 1950s, radio broadcasting took on much the form it has today – strongly focused on music, talk, news and sports, though drama can still be heard, especially on the BBC.
International radio 
In Britain, radio broadcasting was dominated entirely by the BBC, which since the early 1920s had been developing a broad spectrum of programming including different genres of music and speech, including documentaries, drama, comedy, news, religious broadcasts, children's programmes, schools broadcasts and sports coverage). BBC output was a unifying force within British culture, and has been written about extensively elsewhere.
In the 1950s, a small but growing cohort of Rock and pop music fans, dissatisfied with the BBC's output, might listen to Radio Luxembourg, but to too small an extent to have any impact on the BBC's monopoly and invariably only at night, when the signal from Luxembourg was stronger. During the post-1964 period, western Europe offshore radio (such as Radio Caroline broadcasting from ships at anchor or abandoned forts) helped to supply the demand for the pop and rock music. The BBC launched its own pop music station, BBC Radio 1, in 1967.
In South Asia, Radio Ceylon was the oldest radio station in the region. Broadcasting in Ceylon was launched by British engineer, Edward Harper in 1925. Radio Ceylon became a public corporation in 1967 and was known as the Sri Lanka Broadcasting Corporation when the island turned into a republic in 1972.
Interest in old-time radio (OTR) has increased in recent years with programs traded and collected on reel-to-reel tapes, cassettes and CDs and Internet downloads, as well as the popularity of podcasts.
See also 
- Audio theater
- Freeform radio
- History of radio
- List of old-time radio people
- List of old-time radio programs
- List of radio programs
- Radio promotion
- "Kultur og underholdning" (Norwegian) – English translation by Google translate
- Spiegel, Jan Ellen (2007-09-09). "We Interrupt This Play for a News Bulletin on the War". The New York Times. Retrieved 2007-09-09.
- "Radio Dramas". Regina A. Quick Center for the Arts. Fairfield University. Retrieved 2008-04-18.[dead link]
- Necrology of Old Radio Personalities
- "OTR Actors and Their Roles"
- Internet Archive with OTR Programs