Double Layer DVD R

[Guyute]

Here it is in a nutshell:
when a laser hits the copy layer in the CD, it leaves a hole (like a lens will focus sunlight and burn a hole in paper). This creates pits in the copy layer.
would look like this if viewed side-on:--_--_---_-___--__---_-

+R means the info is the unburned layer;
-R means the info is the burned pit. Or vice versa? But that is what the technology does.

[Elspode]

Okay...so then does the DVD burner figure out what you're feeding it and burn the disc accordingly?

[BigV]

Originally Posted by Guyute

Here it is in a nutshell:
when a laser hits the copy layer in the CD, it leaves a hole (like a lens will focus sunlight and burn a hole in paper). This creates pits in the copy layer.
would look like this if viewed side-on:--_--_---_-___--__---_-

+R means the info is the unburned layer;
-R means the info is the burned pit. Or vice versa? But that is what the technology does.

Sorry, no. Regardless of whether it is pits or lands, BOTH are necessary to for any information to be held. One (you choose) represents 0 and the other necessarily represents 1. It is just wrong to think one represents "info" and the other is, what, whitespace?

+R and -R are competing recording formats. From Wikipedeia:

The DVD+R format is divergent from the DVD-R format. Hybrid drives that can handle both, often labeled "DVD±RW", are very popular since there is not yet a single standard for recordable DVDs. There are a number of significant technical differences between the dash and plus formats, although most consumers would not notice the difference. One example is the ADIP system of tracking and speed control being less susceptible to interference and error than the LPP system used by DVD-R, which makes the ADIP system more accurate at higher speeds. Also DVD+R(W) has a more robust error management system than DVD-R(W), allowing for more accurate burning to media independent of the quality of the media. Additional session linking methods are quite a bit more accurate with DVD+R(W) versus DVD-R(W), resulting in fewer coasters due to buffer under-run and multi-session disks with fewer PI/PO errors.

There are some other places where you can safely watch the flamewars over the different formats, interesting if you like the smell of burning polycarbonate in the morning ("smells like...victory"). I couldn't care less, really. I just want to pop the disc in, press the button, and get the finished product to play in another drive. Don't we all?

In service to that goal, it does seem that the +R format has better press as to the error correction capabilities. And of course, it matters a lot what drive you're using. Some of the newer ones are ±R, meaning they'll eat what you feed them and poop out what you want. (ok, that analogy started ok and ended badly, sorry). It is most important to use the media that your drive requires (obviously). If you have a choice, from what I have read, the +R is more robust.

As to the difference in DL ±R, I think the case is even stronger in favor of the +R media, since the two layers need to be recorded to in equal measure in the -R layout. Since DVD players use Opposite Track Progression, that means that the burner needs to fill in a little at the beginning, and a little at the end, then a little at the beginning and a little more at the end, and so on. Seems thrashy to me.

This article is somewhat technical, but does specifically address the differences between the +R and the -R. The author is strongly in favor or +R. My best executive summary:

+R has a more robust (at higher speeds) method for determining the address of a given block. (ADress In Pregroove vs Absolute Time In Pregroove)

+R has a more robust error correction scheme. (Logical to Physical address translation for remapping bad blocks)

+R wastes less space on multisession recordings. (4MB per boundary versus 32MB to 96 MB per boundary)

He goes on (and on) and even says he's restricting his list of comparable characteristics. I read it and understood it, but I think the differences are largely academic since the article was written so long ago. The hardware has caught up a lot in the meantime and I think the differences are still true, but matter less. Good luck, Els.

[Elspode]

Dude...that was exactly the sort of info I was looking for, and precisely what I couldn't seem to find anywhere online. Guess Wikipedia never came to mind for me.

As I just replaced Mrs Elspode's dead DVD burner with a shiny new one just like mine, we are both now +/- compatible (she could only do - before), and so I shall grab me a short stack of +R double layers.