Radio stations are private or public broadcast centers that broadcast sound. Initially, the radio stations used transmitters to broadcast sound as radio waves. Today, radio stations use cable FM, local wire networks, satellite and the Internet to broadcast sound.

Most radio stations use pre-recorded material like music and talk shows; some even use computer sequencing to run programs. However, the big radio stations run the programs live, that is in real time, and are extremely popular.

The first radio stations to make it big were the AM radios. These radio stations derived their name from the technology that was used to broadcast the radio waves -- amplitude modulation. These broadcasts were made in the range of 530 to 1700 kHz, which is popularly known as the standard broadcast band, and were the dominant form of radio broadcasting till the late eighties.

Next came the FM radios. These radio stations transmit in the 88 megahertz and 108 megahertz band but their broadcasts are high fidelity broadcasts; the user is assured of high quality sound reception. Expectedly, the FM radio gained quickly in popularity.

However, both AM and FM radio stations can be heard in a limited area only. Their range depends upon the power of transmitters used to broadcast the sound waves. Some college and university radio stations can be heard only within the campus because they use very low power transmitters. The public broadcasters have a much larger footprint because they use high-power transmitters.

The arrival of the Internet radio has changed the broadcast scene dramatically. It is now possible for individuals to set up radio stations that can be heard across the world by users who are connected to the Internet. The result is that there are hundreds of thousands of Internet radio station streaming music and talk shows round the clock.

Another major development has been the emergence of satellite radio. These radio stations use satellites to beam radio programs round the world, making it possible to hear live radio broadcasts in real time.