The Pocket Radio

• The Regency TR-1 was the first radio small enough to be easily carried. The TR-1 was released in 1958 by Regency and Texas Instruments. The developers were able to make the radio smaller with newly invented transistors instead of bulky tubes. Pocket radios became extremely popular in the 1960s.
  
  

Portable Cassette Players

• Technological advances prompted the next step in compact audio device development as well. After the invention of cassette tapes, electronics companies scrambled to market a product to general consumers. Sony developed the Walkman in 1979 at the same time as Toshiba, GE and others released their own stereo cassette players.
  
  

Portable CD Players

• Sony announced the first compact disc player, called the D-50 or Discman, in 1986. While sales were initially slow, consumers gradually began to favor the CD's improved sound quality and other companies began to release their own portable CD players.
  
  

Digital Audio Players

• German software engineers developed the MP3 format in 1989 but it was not until 1998 that both Eiger Labs and Rio developed players that could play audio compressed into MP3s. The digital audio player came to the forefront of portable audio technology when Apple released the 5GB iPod in 2001.