Here's what I noticed that may interest fellow CD/DVD/BD/optical storage freaks, on a SEGA Dreamcast disc back in November 1999, with a Sony D-E446CK audio CD player, with its door sensor altered so that the player played even with the door open:

1. I had a SEGA Dreamcast demo disc which had several audio (CD-DA) tracks on it in the compressed section of the disc.

2. I inserted a regular music CD of decent length (anyone wanting details: it was Mythos - Mythos (1998), 63 minutes; but this doesn't matter much -- only length matters) and opened the door, whilst the CD was playing a late track.

3. I removed the spinning disc carefully, but quickly, so I can quickly insert the Dreamcast disc whilst the laser stayed at that position 'thinking' that the music CD had a bad scratch.

4. Upon insertion, I noticed that the track/time display changed from '09  02:25' to '03  67:07'! That CD player silences all data tracks, so I only heard nothing. As this was playing, I held down the FF button and around 90 minutes or so into track 03, the track advanced to the next one, which was CD-DA! I also tried rewinding backwards in track 03 (really Session 2, Track 01) and my CD player went as far back as around 07:10 before refusing to rewind (probably reached the session change point?).

5. I believe the laser was struggling to read tracks 04 & 05, as the audio was clicking a bit, like on a CD with circle scratches, which makes me believe that these so-called 'GD-ROMs' are just physically compressed CDs (a la today's GigaRec, by Plextor) with SEGA Saturn's protection, or just a complete (disc closure-style) lead-out at the end of session 1.

6. There was another track on this disc (06) and it 'ran' for around 71 minutes before reaching teh end of the disc.

What does anyone here think of this? Could it be that the 'GD-ROM' is just a CD with Saturn copy protection & physical GigaRec-style compression?