SEGA Dreamcast 'GD-ROM': Really just an old GigaRec-style thing + Saturn protection?

vbimport

#1

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 sectiion 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 7 minutes & 10 seconds before refusing to rewinding (probably reached the session change?).

  5. I believe the laser was struggling to read tracks 04 & 05, as the audio was clicking a bit, like on a CD with circumfrential (sp?) 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 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?


#2

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


#3

Hmm. I forgot about NAOMI using GD-ROMs too. Are these discs arcade DC games or totally different? It would be cool to even rip using a DC one of those discs and get a chance to play it in the DC (this is stretching it, though!).


#4

I posted something about this issue in the Sega Saturn thread.

Sega DreamCast discs utilise the same authentication mechanism as the Sega Saturn.

The blank ring contains embossed pits that make the human readable text with the the Sega trademark and copyright text. It is checked for a reflectivity index and then dependant upon the results of those tests, it will either yield an authentication challenge pass or fail.

The high density region is just that, a simple high density endcoding of standard CD-ROM sectors. The density has been increased, much in the same way that Plextor have utilised many of Yamaha’s old patents to perform it in their GigaRec.

I think that you will find that many decent CD and DVD ROM drives should have little to no problem actually reading the high density area, as even though it is outside the scope of the original CD specifications, the tolerances today are more than good enough to enable reading of said areas.

2/3


#5

OK. If the DC relies on these embossed pits, how do you explain self-booting burned games? I have about 30 of these self-booting CDI images currently and when I burn using Alcohol 120 %, they run in my DC just fine, as if I had a modified DC, when my DC was never messed with.

Secondly, is there any way to force the PC CD drive to read starting at a certain sector & output to, say, a BIN or ISO file?


#6

There is a back door in the DreamCast that allowed the booting of specially constructed CD’s. That’s all there was to it - apparently the programmers/designers didn’t expect that anyone would find it… It was a silly mistake that cost them (and Sega Enterprises, eventually) dearly.

As for your question: All that software can do is request from the drive that a certain sectors content is read and returned, it is up to the drive itself to return the data at the sector location that the initiator requests.

If your drive will not return the data from the region you request, then generally the answer is a no - but there are ways: some people have found that they can swap the disc without the drives logic detecting the swap and then send the drive to read into the region they desire.

It is messy (for many reasons) but it does work, albeit is problematic.


#7

I actually don,t really think it looks for the reflectivity thing, butfor a no more than 45000 lba track closed with a ip00000.bin as the bootsector and then, it looks at 45000 to get the real game.

It may got another check, like to check for BAD sectors in the ring instead of reflections but I really don’t think they’d have create a reflectivity check, since the drive look 100% normal, there’s nothing to check reflectivity … and I’ve took it apart many times to hack it a little.

A clue might be the weird BIP it does when A game is booted (I think only original gd-roms) … what might do this ? the lens getting in HD mode ?

Maybe they put some kind of weird lead-out too …

Well, that’s only speculations of course, about what I’ve noticed.

ps: to read a gd-rom in a pc dvd drive is kinda easy. but even if almost every drives can read the ip.bin (45000-45016) many can’t go further(ltd-165h works well) I’ve done thi often and THPS2 and TOys COmmander works 100% ripping throught drive)

Does anybody know the gd-rom connection pinout ? I’d like to have some infos about it …

Thank you !

-=FamilyGuy=-