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General Hardware Discussion Hard drives, CD, DVD Monitors, All hardware questions not better served by our other Topics


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  #21 (permalink)  
Old 28th April, 2004, 07:17 AM
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wow i thought this thread was a joke when i read the first 3-4 posts lol! I have a cd of drivers for my mp3 player I made as a back up of the original disc, lets see, goin on 5 1/2 years, works like day 1. I don't believe them!
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  #22 (permalink)  
Old 28th April, 2004, 08:59 AM
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Thanks guys, very interesting! What's the difference between CDs and DVDs?
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  #23 (permalink)  
Old 28th April, 2004, 09:37 AM
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Quote:
Originally Posted by Daniel ~
Thanks guys, very interesting! What's the difference between CDs and DVDs?
They use different lasers. CD's are based on an infrared laser. DVD's are based on a red laser. Because the frequency of the red laser is higher, it can basically read smaller pits on a disk. The same basic idea is why Blu-Ray can hold so much more than a DVD. Blu-Ray, as the name suggests, is based on a blue laser which has yet a smaller frequency. Just wait til they come out with a usable violet laser, or even better yet, an x-ray laser. The problem with higher frequency lasers is that they (at least with current technologies) require much more power to maintain stability in the beam.
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  #24 (permalink)  
Old 28th April, 2004, 09:39 AM
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Quote:
Originally Posted by XeroHouR
wow i thought this thread was a joke when i read the first 3-4 posts lol! I have a cd of drivers for my mp3 player I made as a back up of the original disc, lets see, goin on 5 1/2 years, works like day 1. I don't believe them!
You probably have them stored very well. Also, if they're 5 years old, they're probably made of dyes that are less sensitive than the new ones made today.
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  #25 (permalink)  
Old 28th April, 2004, 09:48 AM
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The difference between CDs and DVDs? From a consumer standpoint, storage capacity.

From a technical viewpoint...
The spiral track on a CD is impressed on the top of the plastic disc, which is then splutter coated with aluminium, and then laquered to protect it. Hence, the data is stored on the top surface of the disk and read from the bottom.
The spiral track(s) on DVDs are in the middle of the disk, between the two polycarbonate discs. Hence, the data is stored in the middle of the disk and read from the bottom.

CD has a single reflective layer. DVD can have a reflective layer and a partially reflective layer to allow a doubling of capacity up to the 9GB mark. When there are two layers on a DVD there's two method for producing the tracks. One is parallel tracks, where both tracks start at the hub and work outwads. The other is Opposite track, where the first track starts at the hub and works outwards, and the second track starts at the outside wand works towards the hub. Opposite track is typically used for video work, as it saves the drive from having to seek back to the hub.

There's also a difference in wavelength. CD drives use a laser that's pretty much near infrared to read the disk. DVD drives use a laser that's more firmly in the red part of the visible spectum. This allows the DVD to pack features (pits/lands and spiral pitch) more closely together, as the higher the frequency of the light, the smaller the features that can be resolved.

Something like that at least!
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  #26 (permalink)  
Old 28th April, 2004, 04:12 PM
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Quote:
Originally Posted by mookydooky
You probably have them stored very well. Also, if they're 5 years old, they're probably made of dyes that are less sensitive than the new ones made today.
i have to agree with that.Think about it.. it took a certain amt of light to burn @ 2x...so how much moer powerful would the light have to be to burn @ 52x?(which is best explained a "reading" the disk at 52x the bit-rate of a standard audio cd)..get the light too strong and it reflects back into the laser array too strong for the eye to read.so, you make the disk more sensitive.
and mookydooky...the reason you explained(the chemicals used) is the most simple "specific" reason ..and hit the nail on the head.
in regards to bluray... they can get 120g i heard by dual layer double sided...but don't quote me.
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  #27 (permalink)  
Old 28th April, 2004, 06:53 PM
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Quote:
Originally Posted by XeroHouR
wow i thought this thread was a joke when i read the first 3-4 posts lol! I have a cd of drivers for my mp3 player I made as a back up of the original disc, lets see, goin on 5 1/2 years, works like day 1. I don't believe them!
Still...wouldn't hurt to make a few new back ups, hey?":O}
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  #28 (permalink)  
Old 28th April, 2004, 08:19 PM
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The article I refered to is now locked to nonsubscribers. But the tester said that he took 30 CD-R's, all different brands, and put them into storage. After however many years it was, 10% of them had failed.

This is just something to be aware of and to take in to consideration when storing things like holiday snaps or important data.

I didn't realise just how sensitive these disks are to light before this discussion. So, I will be keeping my disks somewhere completely dark and cool from now on.
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  #29 (permalink)  
Old 28th April, 2004, 08:32 PM
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I always have, but that was just a storage accident of chance!
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  #30 (permalink)  
Old 28th April, 2004, 09:09 PM
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it was 10 years of storage...and he had some in cryogenic storage as well, which, because @ 0 Kelvin almost nothing moves, hence nothing reacting with the cd-r and them lasting longer...but not forever, and if i remember correctly, it was mostly due to the oxygen in the air reacting with something in the disc(chemical) that facilitated faster burning. it was a planned study on the longterm life of removable media done by some guy with a degree or something. sorry if i'm kinda vague, but the old noggin is gettin foggy
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