The IXI was the world's first

digital audio player A portable media player (PMP) or digital audio player (DAP) is a portable consumer electronics device capable of storing and playing digital media such as audio, images, and video files. Normally they refer to small, battery-powered devices ...

. It was invented by Kane Kramer in 1979. In 1981 Kramer filed for a UK patent. UK patent 2115996 was issued in 1985, and U.S. Patent 4,667,088 was issued in 1987. In 1988 Kramer's failure to raise the £60,000 required to renew the patent resulted in the patent entering the public domain, but he is still the owner of the designs. IXI was around the size of a credit card and had a

LCD A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers to display information. Liquid crystals do not em ...

screen and navigation and volume buttons. Four

prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototype ...

models were built and a pre-production model went on sale at the APRS exhibition at Earls Court in London, in October 1986.

References

Original investor's report on the IXI from 1979 (PDF) Format
Digital audio players Portable media players Portable audio players {{Tech-stub