The Walkman became one of the most successful audio products of the postwar period, and like the Victrola before it, any personal portable cassette player was called a "walkman," regardless of manufacturer. The portable personal stereo was the most important electronics product of the 1980s. Bought by millions of people worldwide, it dramatically changed the way people listened to music. Its convenience and small size dictated the shape and function of the next generation of digital technology. Manufacturer Sony's hunch was right: Americans did buy them in the millions, and the walkman became one of those products that everybody owned, like a television, radio, or VCR.

The introduction of the Phillips compact tape cassette in 1963 was an important technological step in the reduction of size of talking machines. The machines that played them used transistorized, solid-state amplifiers that took up far less room than vacuum tubes. The size...