The tracks are wound even tighter than normal cds from what i remember reading so it could be called GigaRec. The thing that stops most drives reading the discs back is the TOC. Discswapping can allow it to be read back in some drives from what i remember. I have heard people being able to dump GDrom discs by discswapping with certain dvd rom drives.
Heres some info on the discs a bit old now.
The are 3 distinct area's when you look at the bottom of a GD-ROM disc.
The low-density inner track (dark gray) contains about 35 Mb (4 mins) DATA which is also accessible by normal CD-Readers.
The outer track (light gray) contains about 1 Gb (112 mins) DATA but is written in a high density format which can NOT be accessed by normal CD-Readers.
The area between the two tracks (black) doesn't contain DATA and acts like a border. In this ring the following texts can be read:
* Produced by or under license from sega enterprises LTDs
* Trademark SEGA
A normal CD-Reader will only read the first, inner track and won't read past the black area. Even if it could read past the black area then it can't read the high density track.
The details of the high-density region really aren't known, but there are two popular hypotheses. The most popular is that the high-density region has minimal error correction information that's even worse than regular CD audio. Support for this can be found with Sega's unusually excessive warnings on their discs "Handle with care. Scratched discs will not play." Unfortunately if that were true, then all of the discs at Hollywood Video would be broken. The other hypothesis is that the data is stored in CAV/CLV format much like laserdiscs
Talk of read GD discs vial DVD-ROM drive is discussed here i havent read the topic but i think they did>>>>>> http://www.emutalk.net/showthread.php?t=25684&highlight=dumping