The original Walkman was released on July 1, 1979. But let's get couple of things straight: Sony didn't come up with the idea, and its success was due to revolutionary lightweight headphones, not the lowly Philips Compact Cassette.
I labored for years under the mistaken belief that Sony invented the
portable personal stereo, culminating in the release of the Walkman in
mid-1979 (it sold only 3,000 units in the first month). It turns out I was wrong. The real credit for such devices
goes to Brazilian intellectual Andreas Pavel, who created the first
portable personal stereo players in the late 1960s.
He was unable to get people to see the magic of the device -- no
great surprise, given the massive earmuff headphones that were the
state-of-the-art in the sixties and seventies. He recounts that, while
he lived in Milan in 1976, "people would look at me sometimes
on a bus, and you could see they were asking themselves, 'Why is this
crazy man running around with headphones?"'
Pavel filed patents in five countries, and Sony agreed to license
his technology in 1986 -- although they refused to acknowledge him as
the technology's inventor. He fought long and hard, and it wasn't until
2003 that he reached an agreement with Sony that saw him credited for
his idea, along with a sizable cash settlement rumored to be over $10
million. To his credit, he never let his legal battle consume him or
define his life, even when faced with financial ruin.
While many people assume that the Compact Cassette tape was the secret behind the Walkman's runaway success, it would have been a dismal flop without the introduction of featherweight headphones with samarium-cobalt magnets.
The original headphones weighed a mere 45 grams. Prior to that, hi-fi headphones were bulky, heavy devices ill suited to jogging or riding the train. Their arrival was a critical and frequently overlooked part of the Walkman's immense success throughout the early 1980s, especially when you realize that the Compact Cassette had been on the market for 15 years before the Walkman set sales on fire.
Walkman 20th Anniversary Press Release from 1999 (oh, how far we've come...)
Giving up my iPod for a Walkman [thanks, Gio and !]