CD: How is data Stored on it?

On a Daily Basis a large of CD’s are sold in market. Now they have been minimized as the other modes of storage have dominated over it. In 2007 there we 200 billion CD sold all over the world but the marked has dropped to 50 % now. Still they are used in many places for storing data on it.

Let’s take a look over its’s technology, how was it used for reading, writing and saving the data.

CD which is known as Compact disk stores data in form of binary digits.

The CD are made of Polycarbonate material of thickness 1.2mm which is coated with aluminium to make it reflective, They have spiral track over their surfaces which have layer of groves on it known as pits, spaces between these pits is called as lands For Example: Consider a muddy area where holes represents pits and space between then is land, Pits are usually 100 nm deep.

To Store the data on CD, infrared laser of wavelength 780 nm is used to save the data on Cd. The laser movement is governed with the help of a precise mechanism, which involves the working of one stepper motors, one dc motor. The Stepper motors give the movement to the laser Step by Step and dc motor rotates the Cd, on Combining both gives accurate motion. During Writing the laser strikes the Cd roms and creates a series of pits and lands on it. The pits and lands do not represent 0 or 1, change in pit or land is considered as 0 and no change as 1. The Series of this pattern represents the data you have stored on CD.

Reading Data on Cd

The data is read with the help of Laser which have mechanism built in it for capturing as well as transmitting the laser. The Laser strikes the Pits, which then detects the depth of the pit by transmitting the reflected light back to the photodiode, change in depths of pits produces different signals which then create corresponding electrical signals and are received as audio or video.

In between playing a sound or video from Compact disks involves working of DAC chip which converts digital signals to the analog ones. The photodetector cam’t give analog signals directly. Therefore digital signals have to be converted into analog ones to be able to play the video or audio form the CD.