CD Vs. DVD
- Thread starter Swane
- Start date
smorizio
Titan
- Jan 22, 2010
- 30,984
- 9
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when cd came out sony set the standard by how much music (a clasical music) could fit on a disk. (90) min or 650 megs.
then it got bump to 720 megs.
dvd as there two layered disks and there two lasers that can read/write through both layers. the size went up.
then it got bump to 720 megs.
dvd as there two layered disks and there two lasers that can read/write through both layers. the size went up.
MauveCloud
Splendid
- May 7, 2010
- 2,830
- 0
- 21,960
There's more to it than just single/dual layer, because even a single-layer dvd stores more data than a cd. Wikipedia has this picture that I think does a good job of showing the differences:
http://en.wikipedia.org/wiki/File:Comparison_CD_DVD_HDDVD_BD.svg
http://en.wikipedia.org/wiki/File:Comparison_CD_DVD_HDDVD_BD.svg
CDs, DVDs, and BRDs (BluRay) have only one thing in common, the diameter of the disk.
Much of the increase in storage capacity comes from the different laser diode used in reading from the optical media.
CDs use a 780nm infrared diode. The light emitted from this diode is not visible to the human eye, but can still burn skin and cause retina damage.
DVDs use a 650nm red diode. The smaller wavelength allows for more elements to be stored on each track, and allows for more tracks to exist on the disk.
BRDs use a 405nm violet diode. Same deal applies as with DVDs, smaller wavelength increases data density as long as the same encoding scheme is used.
Focusing further decreases the minimum size of the storage elements on each disk. BluRay focusing is much improved over DVD focusing, which allows its 405nm diode to read a 150nm pit whereas a 650nm diode on a DVD can only read a 400nm pit. This also decreases the track pitch (the space between tracks) from 720nm to 320nm, doubling the number of tracks per disk.
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