Before there were Personal Computers, CDRs, and Napster, there was the Cassette Deck and its cargo, the Compact Cassette.
Cassette Decks are an audio component that are used to record and play back audio on a cassette tape. Putting audio on magnetic tape is nothing new, the precursors of the modern audio cassette were wire recorders which were around even before World War 2. Magnetic Tape succeeded wire recorders, and in the 1950s bulky vacuum tube type reel to reel recorders were common in radio and TV Studios, and as technology improved, were increasingly being used to record music. As electronics improved and miniaturized, smaller formats for magnetic tape began to appear for use in portable recorders, dictation machines, and so on. The most popular format was the compact cassette which was developed by Phillips for use in dictation equipment, but became a popular medium for portable tape recorders and telephone answering machines by the late 1960s, but the audio quality of most of these devices was well garbage. The poor quality of the early mechanisms also resulted in the machines frequently eating the tapes.
The invention of Dolby Noise Reduction made quality audio possible from the small cassette tape, and by the mid 1970s stereo cassette recorder-player combinations, commonly known as Cassette Decks were finding their way into racks of audio component systems in large numbers, displacing the other common tape format, the 8-track. Cassette Players were also finding their way into car radios, either as factory options or as aftermarket replacements or add-ons for existing radios, and the popularity of the cassette as a music medium soared. People could tape their vinyl records and take their music with them into their car, or tape a friend's record collection.
Taping became as popular on college campuses as Keg Parties. The RIAA moaned that home taping was killing the record industry. Then as now, they tried moral suasion to convince people to stop the practice, and tried to restrict the sale of cassettes, but their legislative efforts only resulted in a modest tax on cassette tapes. More effective was their effort to stop Album Oriented Rock stations from playing record albums in their entirety.
Cassette decks are ubiquitous today, and even the most modestly priced boombox now has a cassette deck built in, often a dual deck to allow dubbing. CD Players are now eclipsing the popularity of the humble cassette deck, as a single CD can hold up to 12 hours of music on MP3. Although I have both CD and Cassette players in my Honda Accord, my cassettes still see a lot of use. CDs can be ruined by a single scratch, while cassettes can take years of abuse.