Devices that play CDs. Often, they can be used to play both audio CDs and homemade data CDs containing MP3 or other digital audio files. Pocket devices. These are solid-state devices that hold digital audio files on internal or external media, such as memory cards. These are generally low-storage devices, typically ranging from 128MB to 1GB, which can often be extended with additional memory. As they are solid state and do not have moving parts, they can be very resilient. Such players are generally integrated into USB keydrives. Devices that read digital audio files from a hard drive. These players have higher capacities, ranging from 1.5GB to 100GB, depending on the hard drive technology. At typical encoding rates, this means that thousands of songs—perhaps an entire music collection—can be stored in one MP3 player. Apple's popular iPod player is the best-known example. Early digital audio players British scientist Kane Kramer invented the first digital audio player, which he called the IXI. His 1979 prototypes were capable of approximately one hour of audio playback but did not enter commercial production. His UK patent application was not filed until 1981 and was issued in 1985 in the UK and 1987 in the US. However, in 1988 Kramer's failure to raise the £60,000 required to renew the patent meant it entering the public domain, but he still owns the designs. Apple Inc. hired Kramer as a consultant and presented his work as an example of prior art in the field of digital audio players during their litigation with Burst.com almost two decades later. In 2008, Apple acknowledged Kramer as the inventor of the digital audio player The player was as big as a credit card and had a small LCD screen, navigation and volume buttons and would have held at least 8MB of data in a solid-state bubble memory chip with a capacity of 3 minutes' worth of audio. Plans were made for a 10-minute stereo memory card and the system was at one time fitted with a hard drive which would have enabled over an hour of recorded digital music. Later Kramer set up a company to promote the IXI and five working prototypes were produced with 16-bit sampling at 44.1 kilohertz with the pre-production prototype being unveiled at the APRS Audio/Visual trade exhibition in October 1986. The Listen Up Player was released in 1996 by Audio Highway, an American company led