By 2010, hard drives commonly offered as much storage space as a thousand CDs, while their prices had plummeted to commodity level. In 2004, worldwide sales of audio CDs, CD-ROMs, and CD-Rs reached about 30 billion discs. By 2007, 200 billion CDs had been sold worldwide.
The pits in a CD are 500 nm wide, between 830 nm and 3,000 nm long and 150 nm deep.Ī CD is read by focusing a 780 nm wavelength ( near infrared) semiconductor laser through the bottom of the polycarbonate layer. The change in height between pits and lands results in a difference in the way the light is reflected.
