What is the difference between DVD and CD?

[Oifish]

I just want to know the difference between a DVD-ROM and a CD-ROM. I also would like to know what the difference is between a DVD drive and a CD drive?

 

[RaynorWolfcastle]

As you know (or maybe you don't) the basic principle of optical discs such as CDs and DVDs is to read pits on the discs surface (actually I think that technically they measure transitions from pits to flats, but I could be wrong about that). Anyhow, this is done by shining a laser on a surface and detecting the amount of light reflected using a photocell. By altering the CD surface so that the reflectivity changes between a pit and a flat, you the encode 0s and 1s that make up your data.

So, to answer your question, the DVD format specifies a red laser as opposed to the infrared laser used for CDs. Since the red laser has a shorter wavelength than the infrared laser, it can be used to distinguish smaller features. This means that you can make shorter pits and pack them more tightly together. Obviously by packing things more closely together, you can store more information on the same area and this is why DVDs can hold more information than CDs.

I've skipped over a lot of the details, but this is the gist of it. There's also a specification for dual layers on DVD that didn't exist for CDs to further enhance capacity. Finally, the next generation formats such as Blu-Ray and HD-DVD make use of blue lasers that have an even smaller wavelength that can be used to distinguish even smaller features.

There's a more detailed explanation here if you'd like to read more:
Text

 

[Oifish]

Thats really interesting. Do you know if they are trying to develop one that uses ultraviolet or higher. Gamma mabye (hah)

 

[Safeway]

Pit size, laser, ...

 

[corkyg]

Originally posted by: Oifish
Thats really interesting. Do you know if they are trying to develop one that uses ultraviolet or higher. Gamma mabye (hah)

I think you may be referring to the newly developed and emerging Blu_ray standard.

Blu

 

[JDCentral]

Yeah.. all the newer 'high capacity optical disks' use another wavelength.

 

[aplefka]

Originally posted by: Oifish
Thats really interesting. Do you know if they are trying to develop one that uses ultraviolet or higher. Gamma mabye (hah)

Highly doubt they'd use gamma anything as it's pretty radioactive, and even the most hardcore computer users wouldn't wanna do that.

 

[Continuity27]

Once we get to ultraviolet there will be little push to use shorter wavelengths for a while, the next push will be utilizing the third dimension, by splitting the laser into millions of beams that all focus on different portions. This is known as a holographic disc, and it's already being developed.