The famous German composer Ludwig van Beethoven (born 1770, died 1827) is responsable for the size of nowadays CDs and DVDs.

How came that the great composer could govern the size of a sound carrier more than 150 Jahre after his death - a sound carrier he would not have dreamt about in his lifetime?

Beethoven's Ninth Symphony was Sony vice president Norio Ohga's favourite music piece.

According to Norio Ohga's order the Ninth Symphony absolutely had to fit onto the silver discs in order to avoid an interruption of music enjoyment by changing the discs. The commonly used vinyl disks at that time had a capacity for a little bit more than 30 minutes of music in the best case.

In musical director Wilhelm Furtwängler's version from the year of 1951 the symphony was exactly 74 minutes long. From the technical point of view 74 minutes of music requested a diameter of 12 centimetres (4.72 inches) of the new silver discs. Against this background it can be regarded as quite sure that Beethoven set the standard for the new CDs. 

The later invented DVDs have got the same diameter, however not for reason of data capacity but for device compatibility.