Disc shapes and diameters:
A Mini-CD is 8 centimeters in diameter.
The digital data on a CD start at the center of the disc and proceeds toward the edge, which permit adaptation to the different size formats available. Normal CDs are available in 2 sizes. The most common size is 120 mm in diameter, with a 74- or 80-minute audio facility and a 650 or 700 MB data capacity. This diameter has also been adopted by afterward formats, including Super, DVD, CD, Audio, HD DVD, and Blu-ray Disc. 80 mm discs ("Mini CDs") were initially designed for CD singles and can store to 21 minutes of music or 184 MB of data but never really became famous. Today, nearly every single is released on a120 mm CD, known as a Maxi single.