Cassettes are constructed from two spools inside a plastic casing. Between the two spools is wound a flat plastic tape that is coated with ferric oxide. Once this tape is magnetized, it remains magnetized for as long as the cassette remains intact. For the tape to become magnetized, an electromagnetic signal must be pressed on the tape, activated by its interaction with the ferric oxide. The “A” side of the tape is inscribed on the left and right side with audio channels; the same for the “B” side. The electric signals from the now-magnetized tape are then transferred onto the audiotape. This audiotape is stretched between capstans, or metal spindles. These spindles turn, threading through the main spools to which the tape is attached. A motor turns those spools, and the cassette, as long as the spools continue to rotate, will play its music.
Cassette players became extremely important to the development of how we listen to music, because cassettes made music more portable than ever before. By the end of the 80s, Sony had released its Walkman, which would become the most popular device with which to listen to music—with headphones, also a major shift in the way people interact with music, especially in public. These cassette players function by taking electromagnetic signals from the cassette tape, and convert those signals into amplified audio sound. That tape, coated in ferric oxide, sends signals, instead of receiving them, and the technologies work together in tandem to produce the music inscribed within the cassette tape.
Cassettes were integral to the spread of punk music, particularly in the eighties. It was well known that one would be able to trade tapes for tapes, and much of the proliferation of punk can be attributed to the network of cassette tapes that travelled between shows and cities.