CD-DA (Compact Disc Digital Audio) is the standard variety of audio CD. This format is also known as "Red Book" format after the particular one of the rainbow of CD standards books that describes it.
CD-DA stores a maximum of 79.8 minutes of audio at a 44.1 kHz sampling rate, though some CDs deviate from the standard by using slightly narrower tracks in order to increase the play time.
A CD-DA has no filesystem, but consists of a continuous stream of audio data in LPCM form (similar to WAV files), with 8 parallel subcode data streams marking track boundaries and providing other metadata. However, computer operating systems will often treat the CD as if it has a simple filesystem containing one audio file per track, allowing the data to be accessed and copied.