Compact discs, or CDs, are optical discs used to store data. Originally, CDs were used to store audio data. Later, the technology was adapted to store general data.
CDs come in many different formats. However, CDs can be viewed in the abstract (at the software level) as strings of 2352-byte sectors. The primary difference between the various formats is the manner in which the 2352 sector bytes are formatted.
Compact Disc Digital Audio: this type of CD uses all 2352 sector bytes to store raw PCM audio.
Compact Disc Read Only Memory: this type of CD uses 2048 of the 2352 sector bytes to store data. The remaining sector bytes are devoted to extra error correction/detection codes.