How exactly are DL discs burned?

[dbminter]

I was thinking about it, and, I realized I don't know how DL discs are burned.

 

 

For instance, thinking about old DVD. Is DVD+R DL written from the inside out. Or inside out then outside in for the 2nd layer? Or inside out for the first layer and then reset to inside and write the 2nd layer inside out, too? Or is to burn each layer at each sector? Meaning, burn a sector at Layer 0's sector first then 1's, or 1's then 0's, if you're only doing one pass? The way I see it is since you're writing instead of reading, changing the laser intensity doesn't do any good unless you do it the opposite way around. Otherwise, how do you prevent burning up the data you've already written? So, it seems that what has to be done is for each sector, both layers are burned in the same "pass," first one and then the other, with Layer 1 first so that the laser intensity can be reduced and burn Layer 0 without burning through and to, thus damaging the data already burned to Layer 1.

 

 

So, LUK, or anyone else how's it done?

[zacoz]

I'd always assumed each layer was burnt in a separate pass, from admittedly skimming threads on the matter, and the fact that people who had their burns error at the layer break were approx 50% through. Wouldn't even like to hazzard a guess on direction though.

[LIGHTNING UK!]

They just focus the beam onto the different layers.

 

When burning the second one, it just passes through the first without really having any impact on it.

[dbminter]

Really? The beam does just pass through the first? I would have thought that for writing, doing that would damage the already burned layer. Ya learn something new every day.

[chewy]

I suspect there is some damage to the top layer. Since i have never seen a really pretty

DL burn scan.

Edited January 21, 2006 by chewy

[LIGHTNING UK!]

Maybe we'll get LFC to do a test.

 

Have him burn JUST layer 1 and scan it, then burn another disc filling up both layers and scan it.

 

Then we'll compare the two!

 

I don't think I've really ever seen a DL burn where only the first layer has been burnt, I suspect most of the scan you've seen are the same chewy - therefore it's probably DL media in general that's not so good as SL media, rather than the scan being bad because the laser has damaged Layer 0 when burning Layer 1.

[chewy]

That would be a very good test, since it would isolate the burn,

be nice to see what a scan of the unburned layer revealed!

I've nicknamed this phantom effect "hazing"!

[dbminter]

I thought by the very "defintion" for DL, both layers were burned, even if you're only burning DVD-5 content?

[LIGHTNING UK!]

No, both layers don't HAVE to be burnt, it is possible not to burn layer 1 if you only have enough data for layer 0.

 

You're advised to burn equal amounts to each layer in order to get the best readability. But for testing purposes, who cares about that! lol