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plmiranda
Member
Joined: 09 Sep 2002
Location: Portugal
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Hi !
Does anybody knows when will be available DVD-R dual Layer 8,6GB ?
And if the usual DVD-Writers like Pionner A-03 or A-04 will be able to burn those kind of DVD-Rs ?
thanks
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jkl
SAYAIN PRINCE
Joined: 09 Jul 2002
Location: BATON ROUGE, LA - U.S.A.
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dual Layered disk are pressed not burned. to keep from going on and on, they will be available to the public when dvd press' are in general use by the public(i doubt ever sinse a press can press about 2 dvd's a second, so you know the cost is much more than probaly every single dvd title available today). and sinse they are not burned, no "usual" dvd-writer will ever be ever to burn them.
_________________
Where I walk, I walk alone. Where I fight, I fight alone.
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big_hed
Member
Joined: 12 Apr 2002
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If you want 8.6GB you will have to get dual sided DVD-R. As plmiranda mentioned, dual layer DVD-R is not possible. I think most work is now going for the new single layer blue-ray DVD, but that is years away, especially for home use.
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solarfox
Member
Joined: 06 Aug 2002
Location: United States
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My (somewhat educated) guess is that it will a very long time, if ever, before dual-layer DVD-R will be available... and if they ever do appear, it's a dead certainty that the current generation of DVD-R recorders will not be able to write to them.
I see this question pop up all the time... I think perhaps a lot of people out there don't quite understand what's going on inside a CD/DVD burner. Let me try to illustrate how this works -- and, by extension, why dual-layer DVD-R is something that, while not necessarily impossible, is much more difficult to make work than you might think.
(warning, bad ASCII art ahead!  ) Note that the following explanation is somewhat oversimplified for purposes of illustration, so as not to get bogged down in unnecessary details. (As the saying goes, an ounce of inaccuracy sometimes saves tons of explanation.)
Consider the construction of a typical CD-R or DVD-R disc:
| Code: |
------------------------------ <-top polycarbonate layer
============================== <-reflective layer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ <-organic dye layer
------------------------------ <-bottom polycarbonate layer |
The organic dye layer is made up of a substance which is normally transparent (or at least is optically transparent to the particular frequency of laser light which is used to read the media), but which becomes opaque when "burned", i.e. when hit with a burst of laser light at a particular frequency with sufficient power. (Which is why CD-ROM drives cannot be made to write to a CD; their lasers aren't powerful enough to affect the dye layer.) Reading such a disc is a simple matter of bouncing the laser off of the reflective layer behind the organic dye; any "burned" spots in the dye layer will block the laser beam from reflecting back to the sensor and register as a binary "0", while a successful reflection registers as a binary "1".
So, basically, a single-layer DVD is just a refinement of the same CD-ROM technology we've been using for years. Now let's consider how a dual-layer DVD works:
| Code: |
------------------------------ <-top polycarbonate layer
============================== <-reflective layer
:::::::::::::::::::::/\::::::: <-data layer 2
,,,,,,,,,,,,,,,,,,,,/,,\,,,,,, <-semireflective layer
!!!!/\!!!!!!!!!!!!!/!!!!\!!!!! <-data layer 1
---/--\-----------/------\---- <-bottom polycarbonate layer
/ \ / \
_||_ |_| _||_ |_|
LASER SENSOR LASER SENSOR
reading reading
layer 1 layer 2
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The way a dual-layer disc is read is by using some very tricky, precise optics to focus the laser to a particular depth, enabling it to either bounce off of the closer, semireflective layer or the deeper, full-reflection layer. This enables the sensor to "see" layer 1 or layer 2, as needed. (Exactly how this is accomplished is well beyond the scope of this simplified explanation - in a nutshell, though, the data layers on a "pressed" disc don't actually block reflection of the beam, the way a burned dye layer does; instead, they change the reflection angle so that the laser either hits or misses the detector.) Notice, though, that in order to "see" layer 2, the laser must pass through layer 1 and the semireflective layer both on its way in and out of the disc.
If you think about it for a moment, I'm sure you can see what this would mean for a dual-layer DVD-R. Theoretically, a dual-layer DVD-R would have to look like this:
| Code: |
------------------------------ <-top polycarbonate layer
============================== <-reflective layer
{{{{{{{{{{{{{{{{{{{{{{{{{{{{{{ <-organic dye layer 2
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, <-semireflective layer
}}}}}}}}}}}}}}}}}}}}}}}}}}}}}} <-organic layer 1
------------------------------ <-bottom polycarbonate layer |
So: how do you burn the second layer? The obvious answer would be to focus the laser onto the deeper layer, right? Well, maybe - except that how do you keep the laser from burning the dye in the first layer as well, as it passes through it on its way to the second? That beam will have a fair amount of power behind it (more power than would be needed to burn layer 1, in fact, since it has to reach layer 2 with enough energy left to burn the dye and some of the beam's energy will be lost passing through the intervening layers); even if the beam isn't focused on layer 1, it can still "scorch" it enough to corrupt the data.
Also note that since the laser has to go through layer 1 to record layer 2, you'd obviously have to record all of layer 2's data first, or else the burned spots on layer 1 would prevent the writing laser from ever reaching layer 2. And, finally, there's also the question of whether or not the read laser would be able to see layer 2 properly during playback, since you have a layer 1 which consists of spots that physically block the laser beam from reaching the reflector, rather than one which alters the reflection angle. (Small but critical difference between pressed and burned discs!)
When you add all of these things up, you can see that a dual-layer DVD-R is a very tough engineering problem, particularly if you want to remain backwards-compatible with existing DVD players. Basically, the only way I can see it being made to work is as follows:
* You need some kind of data-recording material for data layer 1 which, when "burned" by the laser, changes the reflection angle in a manner consistent with a pressed DVD's layers, rather than becoming opaque and blocking the laser entirely.
* The material for data layer 1 will need to be burned at a much higher power, and/or at a significantly different laser wavelength, than layer 2 so that the process of recording to layer 2 doesn't corrupt layer 1.
* Your DVD-R recording software will have to be intelligent enough to figure out what goes on what layer (or give you control over it) -- and smart enough to burn layer 2 before layer 1.
* Your DVD-R(W) drive will need appropriate optics to allow it to focus the recording laser to different depths... (and, as seen above, will probably require two entirely different recording lasers, which further adds to the weight and complexity of the optical block.)
* Your DVD-R(W) drive will [i]also[/b] need to know how to record layer 2 in a reverse spiral, since that's the way most dual-layer DVD's are done. (By mastering layer 1 with a center-to-edge spiral, then layer 2 with edge-to-center, you make it easier to switch layers in mid-programme, since the optical block doesn't have to retract all the way back to center before it can begin playback of the second layer.)
While none of these are insurmountable engineering problems, they're not exactly easy to solve, either... and since you would almost certainly need a new DVD-R(W) drive, and new software, to make use of them, it'll probably be a while before any of the major manufacturers even attempt to solve this problem. The "plus-R / dash-R" incompatible-standards brouhaha is already keeping a lot of people from investing in recordable-DVD until the mess shakes out; introducing Yet Another Incompatible Format would only confuse, divide, and probably drive away the market even more.
Of course, I would be happy to be proven wrong...  Unfortunately, based on what I know of the process, I don't think dual-layer DVD-R is gonna happen anytime soon.
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jkl
SAYAIN PRINCE
Joined: 09 Jul 2002
Location: BATON ROUGE, LA - U.S.A.
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so you are saying dual layerd are pressed and not burned, right
_________________
Where I walk, I walk alone. Where I fight, I fight alone.
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sbueffel
Member
Joined: 04 Sep 2002
Location: Portland, OR
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Solarfox, thanks for that excellent explanation. Very clear and informative.
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drewson99
DigiMember
Joined: 02 Jun 2002
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how many times have we seen this topic posted? where can I get a burner that BURNS dual-layer discs? Are there dual-layer blanks? etc...
its actually a pointless endeavor, the whole point of the dual layer fromat is the simplicity of burning two discs and pasting them together. trying to burn the two layers after they are glued together is defeating the purpose, and the next "dics" type media will be out before they would ever figure out a solution to attempt this round-about way of 9.4GB discs anyway.
just reencode if it is a dual layer, it is very easy! Plus, a lot of dvds are on single layer discs, there are lists of these somewhere on this forum.
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solarfox
Member
Joined: 06 Aug 2002
Location: United States
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JKL - all mass-produced DVD's (and CD's ) -- regardless of the number of sides or layers -- are pressed, not burned. The only time you will find "burned" discs being sold with programme material already on them is if you're buying a one-off product (such as what you'd get from a service bureau offering to convert your old home movies to DVD), or something with a very low production run (such as an in-house training video for a small company which may only need a dozen copies made.)
The only discs which are burned are DVD-R(W) or DVD+R(W) discs. Commercial DVD's, such as you find on the shelves at Best Buy or Wal-Mart, are never burned discs; they are always pressed.
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solarfox
Member
Joined: 06 Aug 2002
Location: United States
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sbueffel -- Thanks, I'm glad you found it useful.
drewson99 -- I'm sorry that you think it's a pointless exercise. For your information, though, I can think of quite a few reasons why I would like to have dual-layer DVD-R capability, if such were possible -- and they don't include being able to make copies of commercial dual-layer DVD's without reencoding. I, personally, have a lot of old TV shows recorded on VHS -- entire series which are rarely if ever re-shown these days (and many of which have probably been forgotten) -- and they would take up a lot less room on the shelves if, by using dual-layer / dual-sided DVD media, I could have them recorded eight 1-hour episodes to a disc, with an entire 23-episode season in a single triple-disc case, as opposed to only 2 or 3 episodes per disc with that same 23-episode season spread across a half-dozen DVD cases.
And the reason why this question comes up so much is probably because most people don't know why it isn' t possible, or why dual-layer DVD-R doesn't exist yet. Hence, the lengthy explanation I posted -- personally, I find people generally respond better to an actual, informative answer to their question, even if it isn't the answer they were hoping for, than to a "this is a stupid and pointless question" response.
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plmiranda
Member
Joined: 09 Sep 2002
Location: Portugal
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Thanks a lot everybody !
I really learned a few things with this posts... 
solarfox, thanks for your detailed explanation !
best regards,
plmiranda
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