Digital Audio Tape (DAT) - a magnetic tape technology used for backing up data. DAT uses 4mm cartridges that look like thick audio cassettes and conform to the DDS (Digital Data Storage) standard. DAT tape libraries hold from a handful to several hundred cassettes. DAT was initially a CD-quality audio format. It was thought to replace analog audiotapes for consumers, but wound up being used by professional musicians and sound studios. In 1988, Sony and HP defined the DDS format and quality level for computer storage. Like videotapes, DAT uses helical scan recording.