That's true (if it can't play dvd rom, it most likely can't play any other dvd disc type). However, that is only the logical layer of the disc. One must also consider the signal layer of the disc.
DVD-ROM specifications are not the same as DVD+R specifications.
For instance, DVD specifications set the DC jitter limit at 8% of the bit clock period (for the channel being read) for DVD-ROM and DVD-R.
For DVD+R this limit is 9% of the bit clock period (same timing window size).
So, at least in theory, it is possible to make a disc that is a within specifications for DVD+R, but does not conform to a player that can play back all DVD-ROM conformant discs (but no more).
Or in set theory terms: dvd+r and dvd-rom sets are partly overlapping. The part that overlaps contains those DVD+R discs that are bitset to dvd-rom AND the dc jitter of which is <8% of the timing window.
So, it would be possible for a dvd+r (bitset to dvd-rom) to be 'unreadable' in a player that can read DVD-R discs (if the drive is really jitter sensitive). In reality, this is howerever quite unlikely.
But then again reality can be even more muddled.
One thing that I've learned in my short optical storage journey is that specifications are not reality: you cannot take a walk inside a map. It's just a picture of what reality looks like, but not always accurate.
PS This is very academic, mainly for the amusement of myself and Iggy. For those worrying about compatibility: dvd+r with bitsetting is more compatible (Iggy and I both agree on that).
< Message edited by Halcyon -- 10/27/2004 2:38:04 PM >