Did you know

1. Early CD and DVD drives read data at a constant rate. The data on the disc is passed under the read head at a constant rate (Constant Linear Velocity, or CLV). As linear (meters per second) track speed grows at outer parts of the disc proportionally to the radius, the rotational speed of the disc was adjusted according to which portion of the disc was being read. Most current CD and DVD drives have a constant rotation speed (Constant Angular Velocity, or CAV). The maximum data rate specified for the drive/disc is achieved only at the end of the disc's track (discs are written from inside). The average speed of the drive therefore equals to only about 50–70% of the maximum nominated speed. While this seems a disadvantage, such drives have a lower seek time as they do not have to change the disc's speed of rotation.

2. Compact disc (or CD) is an optical disc used to store digital data, originally developed for storing digital audio. It is the standard playback format for commercial audio recordings today.

A standard compact disc, often known as an "audio CD" to differentiate it from later variants, stores audio data in a format compliant with the Red Book standard. An audio CD consists of up to 99 stereo tracks stored using 16-bit PCM coding at a sampling rate of 44.1 kHz. Standard compact discs have a diameter of 120 mm, though 80-mm versions exist in circular and "business-card" forms. The 120-mm discs can hold 74 minutes of audio, and versions holding 80 or even 90 minutes have been introduced. The 80-mm discs are used as "CD-singles" or novelty "business-card CDs". They hold about 20 minutes of audio. Compact disc technology was later adapted for use as a data storage device, known as a CD-ROM.