Digital Data Storage (DDS) is a format for storing and backing up computer data on tape that evolved from the Digital Audio Tape (DAT) technology. DAT was created for CD-quality audio recording. In 1989, Sony and Hewlett Packard defined the DDS format for data storage using DAT tape cartridges. Tapes conforming to the DDS format can be played by either DAT or DDS tape drives. However, DDS tape drives cannot play DAT tapes since they can't pick up the audio on the DAT tape. DDS uses a 4-mm tape. A DDS tape drive uses helical scanning for recording, the same process used by a video recorder (VCR). There are two read heads and two write heads. The read heads verify the data that has been written (recorded).