NEC PC-Engine CD-ROM² Formats

[MrTikki]

Hi there. I've been seeing a lot of PC-Engine dumps coming through here lately, and was hoping someone might be able to shed some light on the CD-ROM² / Super CD-ROM² / Arcade CD-ROM² formats.

How are these formats different from traditional CD-ROMs, and is there anything special for dumping them correctly? The cue files associated with them look insane...

Cheers!
-MrTikki-

[GreyFox]

A lot!? Nah just a few.

Maybe FB or pablo can go into more detail about the formats themselves...

But as far as dumping goes they are really not different to most.

You do cdtoimage_d8 dumps + subdump.
DIC in 2 runs done for checking on TOC Vs Sub desync.
Maybe verify with some other app...

And that's pretty much it.

[MrTikki]

Thanks for the info, GreyFox. Any thoughts as to why NEC chose to call it CD-ROM²? Was it just a marketing ploy, or is there a unique TOC structure behind the scene?

I'm mostly asking for because I can't seem to find anything the difference online...which is unusually odd. 

Thanks!
-MrTikki-

[F1ReB4LL]

Dunno, what to say about the formats. Many CDDA + many data tracks, like https://redump.info/disc/23664/ -- to optimize the seeking (like those dummy files on PS2 and DC discs to move the data to the edge of the disc). 2 data tracks -- https://redump.info/disc/18514/ -- last track is a backup in case the disc gets scratched or something. Sometimes only 1 data track -- https://redump.info/disc/16749/ (goes last), https://redump.info/disc/9957/ (goes second). Sometimes no audio tracks at all, only 1 data track - https://redump.info/disc/3039/. Game Express CD games have a completely different format (regular ISO9660, in fact - 1st track data with all the files visible, the rest are CDDA tracks). Latter homebrew\unlicensed Super CD-ROM² titles have interesting formats, but I don't have any of these physically, so can't say anything atm (they are close to Game Express CDs, afaik).

As for dumping nuances - CD-ROM² titles (green/blue side stripe) often have sub/TOC tracks addresses desyncs (point to different nearby sectors) -- https://redump.info/disc/2410/, so the subdump .sub is a must. Some discs contain empty sectors in data part - https://redump.info/disc/32499/. Pregaps are usually ECMA-130\yellowbook-compliant (at least 75 sectors in the same mode as the previous track, at least 150 sectors in the same mode as the next track, so the gaps between audio and data tracks are 3 secs long, 1st sec audio, 2 secs data), but sometimes are not - https://redump.info/disc/31791/.

Dunno about "CD-ROM²" name story, maybe, they wanted to point that it's so amazing that it's "squared" times better than usual CDs, lol.

[MrTikki]

Thanks for the thoughts, F1ReB4LL.

Honestly, the only reason I can think for why NEC would re-brand their CD-ROM format as the Super CD-ROM² is if it featured some kind of extra data protection or proprietary file structures that were superior to those found on standard CD-ROM technology.

But since it appears the CD-ROM² format doesn't really stray away from the ISO9660/CDDA standards (it's just more complex in its structure), my suspicion is that they simply wished to brag about how their complex disc structures in some way made their PC-Engine CD / TurboGrafx-CD systems run better or more securely than those using traditional CD-ROMs (or something like that). I only say this because this was done in a day when programmers couldn't be lazy about speed issues. Every millisecond mattered. 

I suspect if I really want to answer this question I'll need to get a hold of some of the original developer hardware manuals. I just don't see why NEC would go to all that effort to re-brand something like the CD-ROM when they were already having to license the technology from Sony. 

Cheers!
-MrTikki-

[F1ReB4LL]

Honestly, the only reason I can think for why NEC would re-brand their CD-ROM format as the Super CD-ROM² is if it featured some kind of extra data protection or proprietary file structures that were superior to those found on standard CD-ROM technology.

Super CD-ROM² system cards have some additional RAM (CD-ROM² cards have only BIOS), so the games are more advanced. Arcade CD-ROM² cards have even more RAM. CD data format is the same.

As for the "why not regular ISO9660" - I've mentioned already, that CD-ROM² discs can be optimized for faster seeking using multiple data tracks + there can be an additional backup data track.