Mini Disc (commonly abbreviated MD) is an optical disc-based data storage format that uses a disc roughly half the diameter of a standard compact disc, except it is housed in a cartridge (roughly 7 centimeters square) with a sliding door; not unlike the way modern floppy disks are housed. The format, developed by Sony in 1991, was originally designed for data and music, and many thought would eventually replace CD as the media of choice. However, for a variety of reasons, not the least of which was limited storage space and (ironically, in light of the popularity of MP3′s now) reduced fidelity due to the ATRAC compression required to make a full CD’s worth of material fit, they never quite caught on. However, after they were pretty much abandoned as a data storage format, and after better versions of ATRAC became available, they did become moderately popular as a convenient and relatively high quality medium for audio recordings both at home studios and broadcast applications. The mini disc has maintained a foothold in those areas, and nowadays there are even recording options available that allow substantially more recording time (at slightly lower quality) than ATRAC.