* I have always found it interesting how a DVD disc cant be burned at capacity of a CD in a CD-RW drive similar to how 1.2MB HD Floppies could be formatted to SD 360k many years ago to use newer 5.25" floppy disks in older drives that only supported 360k. It probably has to do with an initialization stripe on the discs at the inner most track that come blank I am guessing for them to be identified as CD or DVD media when inserted into the drive. However it could be more involved than this. I havent researched the matter.
Burnable Discs, both CDs and DVDs, are constructed similarly to stamped discs, but rather than having a master stamped onto them, they are instead stamped with a pre-groove that is effectively a single, massive land. These lands are the parts the lens sees- the laser is fired at it, and it reflects back to the lens because of the pregroove. One can observe this pregroove pretty easily, actually- just take a blank disk and hold it to the light- notice the rainbow of colours? That's the diffraction resulting from the pregroove.
The discs are burned by basically focusing the laser on the dye layer above the pregroove, which causes it to crystallize and become opaque, stopping it from reflecting light. The pregroove is a necessary feature here- and of course CD and DVD disc grooves have widely different track pitch. The pregroove is also used by drives to identify burnable discs, since the pregroove has some very tiny amplitude modulation that is used to encode information about the disc. A Cd-R/RW drive with a DVD inserted basically sees nothing- it's looking for a pregroove or a groove at the appropriate track pitch for a CD, but it can't see one. Even if it could be forced forward to burn, there is no pregroove following the groove of a CD disc, which is necessary- the pregroove is one giant land, and the burned parts are the pits.
This is unlike magnetic media where there aren't really any pre-existing structures exist on the diskette, just diskette drive conventions about how sectors and tracks are laid out, so it's up to the drive. lower-density media tends not to work so well when used as high-density media, particularly for 5-1/4" diskettes, but you could use a 1.2MB drive to format a 360K Diskette as a 1.2MB Diskette. I know because I did it ages ago without even knowing the disks were 360K because the drive was silent on the matter and "Format A:" Formatted as 1.2MB by default.
Interestingly, there was a short time where it was profitable for companies selling diskettes to market 1.44MB Floppies as 720K Diskettes, so there is a surprisingly good chance that, with the appropriate modifications to the diskette drive or the disk itself, a 720K diskette can be formatted as used as a 1.44MB Floppy diskette. I had a floppy diskette drive modified for this purpose back when it was cost-effective to purchase cheaper 720K diskettes, the infrared detection mechanism which looked for the little hole in 1.44MB Diskettes was removed and instead routed to a front panel switch. Meaning I could flip the switch and have a 720K diskette be detected as a 1.44MB diskette.
