The mini Compact Disc single (mini CD single) was an optical disc format for music singles based on the Compact Disc. Mini CD singles are 3-inches in diameter, compared to full-size CD singles which are the same size as standard CDs, 5-inches. Because of this, mini CD singles are sometimes known as CD3s.
They can be played in most devices that can play standard CDs, with the exception of slot-loading drives. Some CD players require an adapter to play mini CD singles.
The format was first released in the UK in 1988, and most mini CD singles contained at least two tracks, in the same way as 7-inch vinyl singles.
Mini CD singles meet the Red Book standard for Compact Discs, but store less data (about 21-24 minutes maximum).
The format lasted into the early 1990s in the UK, when most CD singles were released on full-size CDs as they were cheaper to manufacture due to their standard size.