BD-RE and CD-RW difference?

[Ryo Destined]

My friend and I had a conversation about what causes the Blu-ray format to have a higher capacity than the other formats. We knew the laser was the main reason, but that didn't explain why you would need a blank blu-ray format disc instead of a standard blank CD to achieve the greater capacity. I've done a lot of research and now understand how rewritable CD's work so I have only speculated one possible reason and I'm looking for confirmation or correction.

My theory is that the dye used in a CDRW or DVDRW or HDDVDRW won't react to the blue laser used for Blu-ray, but BDRE discs have a material that will react to the blue laser.

Please confirm or correct me as to why blu-ray lasers don't provide higher capacity for other blank re/writable disc formats.

[Galley]

The pits are much, much smaller and closer together.

[dv8pdx]

There are several aspects that make the blu-ray disc unique and only writable & readable in the violet laser range.

The blu-ray uses a 405 nanometer laser vs a 650 & 780 nm laser in DVD & CD.
The laser aperture is also increased from 0.60 to 0.85 to allow for a more smaller focused beam on a thinner hard coating on the Blu-ray disc (580nm spot area) than on the DVD or CD. Also, with the data being recorded closer to the surface of the disc, the pits can be deeper plus additional data encoding enhancements also allow for larger writing amount per disc. This beam does not have the same effects when burning on a thicker DVD or CD. Same basic laser wavelength principles apply to DVD vs CD capacity on why you cant store 4.7 gb on a CD.

[Ryo Destined]

That makes sense, but it doesn't seem to totally eliminate the possibility of CDRW holding more data using Blu-ray laser tech. There is a hole I see. The CDRW uses a dye that changes state to either reflect or not the laser, so pit depth doesn't seem to factor. Also, Blu-ray drives can read CDs and DVDs (DVD's definately CDs I'm not sure but suspect due to integration with computers), meaning they can be calibrated for reading those discs using the Blu-ray laser. Theoretically, that means the devices could be calibrated to write on those discs and write in the Blu-ray method. Since a CDRW data layer is merely a dye, then the laser could still write data smaller, the laser would just have to be able to change the dye's state as well as be calibrated for reading from the greater depth of the data from the surface.

I guess there are few other variables. I need to know if blu-ray devices can read standard CDs? If so, can blu-ray drives that you'd put in your computer be able to read and write to a CD? If they can write to a CD, does it use the old red lasers, or does it use the blue laser? If it can write to the disc with the blue laser, why would it have the same size restrictions unless the laser can tell it's writing to a CD and writes the data further apart.

I admit I may be completely missing something to the technology, but please educate me.

[WriteSimply]

Originally Posted by Ryo Destined

That makes sense, but it doesn't seem to totally eliminate the possibility of CDRW holding more data using Blu-ray laser tech. There is a hole I see. The CDRW uses a dye that changes state to either reflect or not the laser, so pit depth doesn't seem to factor.
...
I admit I may be completely missing something to the technology, but please educate me.

Visually three very thin pieces of paper that are white, red and blue. (How American of me). All of them are full with printed text. The white is printed with 12 picas of text size. The red is 6 picas, allowing more text. The blue is 1 pica, allowing even more text.

The way they are put together is always blue in front, red in the middle and white at the back with thin plastic covers in this mini-book, so that you always see the blue first. That is the analogy of how BDs (blue), DVDs (red) and CDs (white) layers are put together, if you were to put all of their layers together in a 5" form factor.

Here is the reason why you can't burn CD-RW as a BD data disc using the paper analogy: due to the thinness of the paper and the tiny text on the blue paper, you can see yet not read the text on the red paper, but you can definitely see and read the text on the white paper. If you were to put the tiny 1 pica text on the white paper, you can't see them through the two layers of blue and red papers.

The BD data layer due to its closeness to the read surface is better at packing more data and have it be readable. If you were to put the BD data layer where the CD layer is, a new error correction algorithm must be invented because there's just so much plastic in between the CD layer and the surface. It would be a whole new disc format since it's neither BD nor CD.

To reiterate: the BD, DVD and CD layers reside in three different PHYSICAL layers on a 5" form factor, requiring three different focal points. It's not just a dye.

I guess there are few other variables. I need to know if blu-ray devices can read standard CDs? If so, can blu-ray drives that you'd put in your computer be able to read and write to a CD?

Yes to both. Most BD DRIVES can burn CD and DVD but not BD.

If they can write to a CD, does it use the old red lasers, or does it use the blue laser?

The Optical Pick-Up (OPU) will switch to red laser to read and burn. The focal point for the red laser will also change between CD and DVD burning.

If it can write to the disc with the blue laser, why would it have the same size restrictions unless the laser can tell it's writing to a CD and writes the data further apart.

Blue laser for BD only. BD drives and burners have blue and red lasers in the OPU, and three different focal points depending on the disc inserted.


fuad

[lch]

burn-able disc all come pre-pitted, so when you buy cd-r,dvd-r,bd-r, the pit are there already which the manufacturer can ensure reliable burn. and the info (media,speed...) is on the inner ring for the drive to recognize.
and the dye for cd,dvd and bd are different.
bd dye is metallic, more expensive. that's why they are going for lth bd which can use normal dye, cheaper.

[betterman]

the -R media really burn the disc, but obvisouly u can't see this.
the -RW media has a electromagnetic field who is induced to simulate the effect burned/not burned

more density of data gives more capacity. no magic.

[SkantDragon]

Blu-rays only look like CDs and DVDs. They're actually made out of totally different materials. Flip a Blu-ray over and look at how the bottom glints in the light, and it actually looks nothing like a DVD or CD.

Even if they were made out of the same materials, we're talking about 71 times more data than the CD disc was designed to carry. Manufacturing tolerances on existing CDs would almost certainly not be tight enough. Minor defects in the dye that wouldn't be noticable at 700MB would be a problem at 50Gb. A lot of the difficulty in developing Blu-ray has been in manufacturing discs with tight enough tolerances and lack of defects to hold that much data reliably.

And even if all of that somehow worked on a CD, it also wouldn't be durable. Blu-rays data layer is _very_ close to the surface of the disc... 0.1mm if memory serves. Even a vague scratch on a CD would destroy it. This is why a hard coat was developed for Blu-ray which makes the discs quite difficult to scratch at all. There's even a youtube video out there of someone taking a pizza cutter to one with no affect.

So yes... what you're talking about seems like it could work in theory, but it's a case where theory and practice are pretty unrelated. Blu-ray uses a lot of the same basic theory, but the underlying technology to make it practical is completely different all the way up and down the process.

That being said, it's likely that Blu-ray technology could be applied to existing CDs to increase their capacity without altering the physical disc specification. It still wouldn't reach anywhere near actual Blu-ray disc capacity. It would be somewhere inbetween (and probably much closer to CD than Blu-ray capacity). However, I don't think anyone is interested in developing such a thing and few would be interested in buying it. There just wouldn't be much point to it.