A disc's storage capacity is determined by the data rate. A high data rate is synonymous with high-quality picture and sound reproduction for movies and music. Taking the CD as an example, let's consider in a little more detail.

A CD has 16 quantization bits, sampling frequency of 44.1 kHz and two channels. This means the data rate is 16 * 44.1k * 2 = about 1,411k (bits/second).

A CD can store up to 74 minutes. When CD-quality sound is stored on a DVD with a capacity of 4.7 gigabytes (37,600 gigabits), the maximum playing time is 37,600 * 1,000 / 1,411 = about 26,648 seconds, or 7 hours and 24 minutes.