Battery operated portable personal music players are fun, enabling users to build a cocoon of their own music.
Portable radios and stereos date back to the invention of the transistor. Over time, these grew in size and power. Enormous stereos run from batteries, “boom boxes,” were commonplace. However, boom boxes played music from speakers and one person’s music is another person’s noise.
Walkman
Eventually, on July 1, 1979, Sony introduced the Walkman TPS-L2, the first portable modern music player. The system featured high-quality headphones and played cassette tapes. Unlike boom boxes, the Walkman was small enough fit in a (large) pocket. At $150 (about $500 USD in 2019). Sony predicted they would sell 5,000 units per month and subsequently sold 50,000 in the first two months. Initially introduced in Japan, the Walkman migrated to the US in June 1980.

Sony dominated portable music in the 1980’s, first with their cassette player and later with a DC version. However, due largely to inter-company conflict, Sony lost the market with the introduction of MP3 technology and digital music. In addition to their electronics business, Sony owned a music and movie studio. Unlike prior technology, MP3’s could make an unlimited number of music copies. Executives at the studio reviled MP3’s due to piracy and refused to release a Walkman that supported the popular MP3 format.
iPod
There were many MP3 players, the vast majority of them underwhelming. Eventually, on Oct. 23, 2001, Apple released the iPod which supported MP3’s. It was not the first portable MP3 player but was substantially easier to use than competitors. Arguing that piracy was out-of-control as people “shared” pirated music tracks over the internet, Apple convinced the studios to allow the company to sell individual songs for $.99.
Quoting articles from the time:
“The iTunes Music Store may be just the thing to get Apple rocking again too. As everyone knows, it’s been a tough couple of years for the computer industry as well. Apple swung back into the black in the first quarter of 2003 after two quarterly losses, but its profits were only $14 million, compared with $40 million a year ago. And as popular as Apple’s iPod portable MP3 player may be, it contributed less than $25 million of Apple’s $1.48 billion in revenues last quarter. So Jobs is betting that by offering customers ‘Hotel California’ for 99 cents, he can sell not just more iPods but more Macs too.”
Songs In The Key Of Steve Steve Jobs may have just created the first great legal online music service. That’s got the record biz singing his praises. Fortune Magazine. May 12, 2003. (emphasis added)
On Apr. 28, 2003, Apple opened the iTunes Music Store for use with the iPod; in the first week, iTunes customers purchased over a million songs. By 2018, Apple’s quarterly revenue was about $60 billion per quarter.

Patents
Andreas Pavel filed patents for a portable music player, called the Stereobelt, in 1977 but failed to sell the idea to any music company. After protracted litigation ー where Sony won and lost various rounds in different jurisdictions ー Sony paid him a substantial settlement in 2003. Kane Kramer held the first broad patent for portable digital music players but lacked funds to renew it and allowed it to elapse before digital music players became popular.