Walkman, stylised as , is a brand of portable audio players manufactured and marketed by Japanese technology company Sony since 1979. The original Walkman was a portable cassette player and its popularity made "walkman" an unofficial term for personal stereos of any producer or brand. By 2010, when production stopped, Sony had built about 200 million cassette-based Walkmans. The Walkman brand was extended to serve most of Sony's portable audio devices, including DAT players, MiniDisc players/recorders, CD players (originally Discman then renamed the CD Walkman), transistor radios, mobile phones, and digital audio/media players. As of 2011, the Walkman range consists exclusively of digital players. Development The Compact Cassette was developed in 1963 by the Dutch electronics firm Philips. In the late 1960s, the introduction of prerecorded compact cassettes made it possible to listen to music on portable devices as well as on car stereos, though gramophone records remained the most popular format for home listening. Portable tape players of various designs were available, but none of them were intended to be operated by a person as they were walking. In the 1970s, Brazilian inventor Andreas Pavel devised a method for carrying a player of this type on a belt around the waist, listening via headphones, but his "Stereobelt" concept did not include the required engineering advancements to yield high-quality sound reproduction while the tape player was subject to mechanical shock as would be expected on a person walking. Pavel later lost his suit claiming the Walkman idea as his own. Sony cofounder Masaru Ibuka used Sony's bulky TC-D5 cassette recorder to listen to music while traveling for business. He asked executive deputy president Norio Ohga to design a playback-only stereo version optimized for walking. The metal-cased blue-and-silver Walkman TPS-L2, the world's first low-cost personal stereo, went on sale in Japan on July 1, 1979, and was sold for around ¥33,000 (or $150.00). Though Sony predicted it would sell about 5,000 units a month, it sold more than 30,000 in the first two months. The Walkman was followed by a series of international releases; as overseas sales companies objected to the wasei-eigo name, it was sold under several names, including Sound-about in the United States, Freestyle in Australia and Sweden, and Stowaway in the UK. Eventually, in the early 1980s, Walkman caught on globally and Sony used the name worldwide. The TPS-L2 was introduced in the US in June 1980. The