A cassette reel is a type of magnetic TAPE storage device used to store audio recordings. It consists of a spool of thin plastic TAPE with magnetic particles embedded in it, which is wound between two reels. The TAPE is played back by passing it over a playback head, which reads the magnetic particles and converts them into an electrical signal. Cassette reels were popular in the 1970s and 1980s, but have since been replaced by digital media such as CDs and MP3s.