[game_preservation] Article about proper SNES emulation

[István Fábián]

Yes, we are going to address the Japanese systems soon and Joseph leads those efforts.

The minimum number for verifying authenticity for most titles is luckily 1 - as long as it was professionally duplicated.

For anything else made with non-commercial solutions (i.e. copied on the same computer platform etc.) ideally, 3 - but naturally it's never 100% certainty for those. It could be just a popular "version" of such disk that got widespread due to rampant piracy...
Unfortunately, it seems that most of the Japanese titles fall into the non-commercial duplication category (with the notable exception of a few Western titles such as Wings of Fury on the x68000), so it will require quite some effort to find copies that we'd have a high enough confidence in for being authentic.

The good news is that the majority of the titles for popular platforms outside Japan were all duplicated and that includes pretty much all 8 and 16 bit formats.
For duplicated disks, it is possible to find inconsistencies in the recording that are not present as long as the disk is not modified (or not written with a home grade equipment, i.e. copy program), that's why it is possible to have an authentic image from a single copy only.
Actually, many copy-protection methods look for various signs of non-commercial duplication in similar ways, but obviously working with higher level data than our tools do.

We'd have to see how well that works for e.g. C64 though, but it is certainly possible to tell about the first 18 tracks of a C64 disk already if it was written on a 1541 drive or a Trace machine, thanks to a mistake in the official Trace scripts supplied for that platform.
This can only be verified with flux transition level dumping, e.g. a device like KryoFlux that is capable of measuring individual flux transitions.
For tracks above 18 we can still look for recording inconsistencies, like we do with platforms using generic MFM controllers (PC, ST, Spectrum, CPC etc) and the same is possible for FM controllers used for Atari 8-bit, as they use the same principle for recording, just encoding itself is different.

Again, verifying authenticity from a single copy is only a possibility with sophisticated analyser technology and low level dumps from disks.

  ----- Original Message ----- 
  From: Devin Monnens 
  To: IGDA Game Preservation SIG 
  Sent: Monday, August 15, 2011 3:14 PM
  Subject: Re: [game_preservation] Article about proper SNES emulation


  Istvan,


  Thank you for clearing that up. To this list, I would also add something else: making a catalogue of what is available for that platform, including version numbers and variations.


  Approximately what percentage of the different platforms have already been archived? I also know there is a group in Japan working on disk-based games lead by Joseph Redon.


     it takes a lot of time of processing the disks afterwards to check the authenticity and integrity of the content.
    Hoping that every disk image made is correct is just wishful thinking considering the age of the media and how common it is to find modified content.


  What is the minimum number of disks to have to verify for authenticity and integrity? Do you need at least two copies to make sure there were no errors? I didn't see any mention of this on the knowledgebase of your site.


    So far we've spent 7 digit amounts to preserve about 3600 titles and to develop the necessary technology - and about 10 years.
    It is however not something that we can really afford to do far longer...


  7 digits in Euros? That would be more than twice the amount in USD! Is Kryoflux helping to solve this problem by distributing the work to collectors and libraries? Have you run into any cases where someone has the game but doesn't have access to a Kryoflux device? If that's the case, it might be possible to purchase one and then mail it from place to place.


  -- 
  Devin Monnens
  www.deserthat.com

  The sleep of Reason produces monsters.



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