Sony Walkman turns 40 years old

Get ready to feel old: It's been 40 years Monday since Sony released its first portable cassette player, the Walkman.

The Walkman hit the market on July 1, 1979, for $150. It became a blockbuster hit, selling 50,000 devices in two months.

The Walkman revolutionized the way we listen to music. In fact, the device became synonymous with all portable music players at the time.

Back then, it used cassette tapes, which evolved into CDs. It dominated portable audio for about 20 years.

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Apple's iPod stole a lot of the Walkman's thunder when it came out in 2001. The Walkman also eventually moved into MP3 territory, but never quite caught on like before.

Tributes to the original titan of portable music are being posted all across social media Monday.

NBC/CNN