Many cars come equipped with a cassette deck, but few people still use tapes as their primary music source. Cassette adaptors are used to play music from an audio device, such as a CD player or iPod, through the cassette desk. These audio accessories resemble a cassette tape with an attached headphone cord, and are available at most retail stores.
A standard cassette has a single component, the magnetic media or "ribbon," which is wound in the cassette and stores each song as magnetic data. The cassette deck contains a component known as a read head, which reads the data stored on the ribbon. After reading the magnetic field emitted by the ribbon, it converts the field to an electronic signal and transmits the signal to the speakers for playback. Some cassette decks have a write head, which converts an electronic signal to a magnetic field for storage on the ribbon.
A cassette adaptor is simply the shell of a cassette tape with an internal write head. It has a short ribbon which spins continuously, but stores no data. An audio cable, usually with a 1/8-inch headphone plug, is attached to the cassette shell and is used to input audio signals from an external device. When the device sends audio through the cable, it is transmitted as an electronic signal. Once this signal reaches the write head inside the adaptor, it is converted to a magnetic field. The field is then read by the cassette desk, converted back to an electronic signal and sent to your car's speakers.