For starters, the digital data is stored in them by the same encoding methods.
The same type of discs are used for both. The process of manufacturing them is the same. The same equipment is used.
What is a CD made of?
A commpact disc is made of a thin layer of aluminium. This alminium layer is embedded in a clear plastic disc.
The diameter of the disc is 120 millimetres or 12 centimetres which is about 4.75 inches.
A pattern of bumps is pressed into the metal layer during the manufacturing process. This is when the digital data is encoded.
The intended data is then introduced into the disc ina spiral pattern along the compact disc.
Think of the grooves on a vinyl record and you'll get the idea.
But then there's a difference.
On a CD, unlike a phonographic record, the groove starts from near the centre of the disc and moves in the direction of the outer edge.
For your information, if you unwind the grrove, the approximate length would be about 3 miles.
For a CD, there need to be no physical touching of the groove for the data to be read.
The CD player just has to focus a beam of laser light on the surface of the CD. This will enable the data track to be read.
How the Data Reading Process Works
Data embedded in a CD has high and low areas on the aluminium surface. In other words, there are deep and shallow areas. Just like along a normal ground.
On the CD the low areas are called 'pits'. As the name suggests, these are 'deep' areas, not visible to the eye, of course.
The flatter areas are called 'lands'.
The laser actually hits these bumps and hollows for the data to be read.
When playback of the disc starts, the disc spins at a rate of between 250 and 500 revoluutions per minute.
It slows down when the outer edge of the disc is nearing.
