Do DATs represent the software, or the physical media?

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Do DATs represent the software, or the physical media?

Post by Lowe0 » 03 Jul 2018 18:35

I was looking into a ROM in my collection that was flagged as a bad dump, Flashback for Genesis. The entry was updated from 12 MBit to 16, the old 12 MBit hashes were flagged as a bad dump, and the new 16 MBit hashes flagged as the only good dump. I asked about it, and the updater responded that they had dumped the ROM chip and updated the DAT entry with their size/hashes.

What I'm wondering is, why flag the 12 MBit version as a bad dump? The case for the game advertises it as a 12 MBit game. The 12 MBit ROM is what I get when putting an original cartridge into my Retrode (MD5 and SHA-1 match). To reproduce the new hashes, I have to force the Retrode to overdump the ROM; the only difference is extra FFs for the remaining 4 MBit.

The same change was made for F-22 Interceptor for Genesis; again, I used my Retrode to overdump the cartridge and was able to match MD5 and SHA-1 for the old and new dumps. The only difference between the two files is extra 00s for the remaining 2 MBit.

It really comes down to whether the DAT entry represents the collection of bytes defined as "the software", or the physical chip those bytes are on. DATs are the definitive identifier for ROMs in RetroArch and elsewhere, so if previously valid ROMs are going to be flagged as bad going forward, then I think some thought needs to be put into why before committing to the change.

Let me know if there's any additional context I can provide. Thanks!

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Re: Do DATs represent the software, or the physical media?

Post by Tauwasser » 03 Jul 2018 20:58

Dumps should obviously reflect the actual ROM chip on the cartridge, i.e. its full capacity and nothing more or less. Having said that, for odd-sized memories, it is important to record whether the unmapped ROM is always driven low, high etc. as it can affect proper running of the software. However, this information should be used to "round up" to the next common power-of-two size.

It depends on the size of the actual ROM chips. I myself found that one Game Boy game was "underdumped" in the sense that there was a bigger ROM chip on the cartridge with the remaining space all being 0xFF that was presumably cut off by the original dumper.

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Re: Do DATs represent the software, or the physical media?

Post by KingMike » 10 Jul 2018 06:25

Luckily I saved all my untrimmed SNES dumps if that becomes the direction we are going.
I think I have only dumped four non-power of 2 Genesis games, aside from the Sonic & Knuckles Lock-On ROMs.
(Eternal Champions and Gargoyles at 24mb, Rolling Thunder 3 at 12mb, and Ghouls 'n Ghosts at 5mb)

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