How does a CD work?

Jonty By Jonty, 11th Nov 2011 | Follow this author | RSS Feed
Posted in Wikinut>Guides>Technology>Computer Software

Information on how a CD works including information on Bits and Bytes, materials used and advantages and disadvantages. Detailed and summaries.

How does a CD work?

A Compact Disc, or CD as it is more commonly named, is simply nothing more than a plastic disc with several layers that make it about 1.2mm thick. A CD works by a laser burning tiny trenches in the data layer of the disc. When you put a CD into a disc drive a laser is aimed at the layer of data and is bounced back (inside of a CD drive right). The computer knows from this whether there is a trench or no trench (bump). A trench is interpreted as a 1 and a bump is interpreted as a 0. This creates lots of strings of 16 bit binary. This means that one binary string can have a decimal value of between 0 and 65535. The diagram below illustrates the use of trenches and bumps.

A DVD works in the same way apart from a DVD has the layer of data in the middle of the disk instead of at the top, like in a CD This means that a DVD can have more than one layer meaning that it can hold a lot more data! It also means that you can have double sided DVD’s – which again increases the data storage amount.

In a Compact Disc there is also a metal layer (also called the reflective layer). The metal is used to reflect the laser beam. Different metals are used in different types of CD’s and DVD’s.

A CD can store between 650MB and 900MB. A DVD can store between 4.7GB and 8.5GB. The only difference between +R and –R is that they used to be made by different companies – like with VHS and Betamax! The –R disc is supported by Pioneer, Toshiba, Sony, Sharp and Samsung. The +R disc is supported by Philips,Sony, Ricoh and HP (The DVD Alliance). Most computers these days will read both +/- but in the early days it was one or the other.

Advantages of CD’s and DVD’s:
- Cheap
- Harder to lose than a USB drive
- Can hold a lot of information

Disadvantages of CD’s and DVD’s:
- Easy to scratch causing loss of data
- Easy to break
- Will become obsolete in the future
- USB and External Hard Drives can hold a lot more data

CD = Compact Disc
DVD = Digital Versatile Disc


65535, Binary, Bits, Burn, Bytes, Compact, Computer, Digital, Disc, Dvd, Homework, Laser, Layer, Mac, Player, Software, Versatile

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