Reflectivity of CDR, CDRW, DVD+R & DVD+RW

[ecnal]

I have heard that when creating a VCD or SVCD it is best to use CDRW rather than CDR media due to it's higher reflectivity. However, I have also heard that when recording a DVD it is best to use DVD+R rather than DVD+RW? Does this even sound correct? Thanks

[sterno]

For CD:

CD-RW is not more reflective than CD-R, it is significantly less reflective (which is why older CD players can't read them). It's often useful to burn to CD-RW to test before writing a final CD, but it's not necessary. Some players play -R but not -RW, and a few play -RW but not -R. Use whatever works and makes you happy.

For DVD:

RW's still seem to have relatively poor compatibility in set-top player, while R's have pretty good compatibility. Use what works in your player.

[DigiToast]

On the contrary, sterno, CD-RWs do have higher compatibility than CD-Rs on most set top players for two reasons. CD-RWs in nature are much closer to that of a DVD than CD-Rs are. RWs must also conform to much stricter specifications and tests than CD-Rs do, thus resulting in much higher quality.

[JHebert]

DigiToast that explanation doesn't make sense to me.
In what respect are CD-RWs "closer in nature" to DVD than CD-Rs?
And if the "stricter specifications" of CD-RW make them more compatible than CD-R, should not DVD-RW and DVD+RW also be more compatible than DVD-R and DVD+R? Tests show this not to be true.

[DigiToast]

CD-RWs are closer in nature to pressed discs (incl. DVDs) because the information you are writing is not simply put on the disc by a dye color change that simulates a pit. Physical pits actually do appear on the disc. CD-RW discs are recorded by the laser heating up the polycrystalline recording compound/layer to 500-700 Celsius, which then melts, gets shifted around to make the pit, and then everything is cooled to keep the pit there after the heating. This.. is the same reason why CD-RWs have been known to conk out on you and suddenly lose data - the recording layer actually changes over time. Also, this is why CD-RWs have a life expectancy of how many times you can reuse it.

[JHebert]

If that is true then why aren't DVD-RW/DVD+RW more compatible than DVD-R/DVD+R? The same phase-change vs dye-layer arguement does not apply or is there another factor?

[DigiToast]

Regarding DVDs, I have no clue about why/how -r/+r would be better than the reusable counterparts. If you want to hear out my suspicions, however, then here it is: What I think might be going on is similar to the original problems that CD-RWs had early into development. Basically, a standard hadn't been set soon enough to make sure that readers would be able to read the media. Thus, the creation of "multi-read" drives. So taking history and applying it to DVDs, just maybe all we need is a "multi-read" standard to be made for DVD readers.

[vitualis]

@ DigiToast: your hypothesis regarding CD-RW is pretty much incorrect. There is no "pit". The writing laser somehow simply change between crystalline and amorphous silicon.

As such, CD-RW is much less "reflective" than CD-R.

I don't know why CD-RW is more compatible in older DVD drives, but it is simply a matter of chance. The optics and laser used in a non-CD-R/W compatible DVD drive simply seems to work better with CD-RW than CD-R.

Remember that a DVD drive uses a different colour laser (635/650 nm) compared to a CD drive (780nm). CD-R discs were only designed to be read reliably by a CD laser and the dyes don't have good optical properties at the wavelength used by a DVD laser.

CD-RW by chance uses a technology that is relatively more compatible in a DVD drive.

However, it should be reminded that the compatibility of both is relatively POOR in a DVD drive that is not designed to read CD-R/W discs.

Regards.

[DigiToast]

Okay so then I'm wrong =). My thinking of amorphous is based on the definition (scientific) that it's a substance without form... thus a crystalline layer on a disc that you would physically change into the amorphous state.. thereby creating what I assumed was a pit.

I don't argue that rws have less reflectability than -rs, but the thought of the data layer resembling more of a physical pit than a simple dye color change was the only reasoning (for the past year or so) that I could come up with for why dvd machines had an easier time reading -rw discs.

Edit/addition: ran a quick search on cd-rw tech and found this..
"Oddly enough, it may be easier for a DVD drive to read CD-RW discs than CD-R discs, because of the way the media is constructed. "
~http://www.cdrfaq.org/faq02.html#S2-12
... it's weird now as I no longer have any idea of how this could be

[vitualis]

Amorphous silicon is just a different form of silicon. It is still there but has different optical properties compared to crystalline silicon.

As I stated before, I have no idea why CD-RW discs are relatively more compatible with non-CD-R/W compatible DVD drives... I just know that they are.

Regards.