Checksum fixing. Useful?

[rwebster]

Hey folks. Some ROM dumps have back checksums and there are tools to fix them. Are they something I should be using?

For example modified ROMs released digitally sometimes have bad checksums.

[dreimer]

And that's the way they are released and the status we wanna verify. Nothing is allowed to be changed at all.

[rwebster]

Understood But for my own use is there a downside to running these with bad checksums at all?

[dreimer]

Depends on the console. Almost every console does not care about bad checksums at all. Many beta ROMs would have big problems though.
Bigger flaws are there if you have a ROM which is released with a bad header.
Like Pokemon Gold/Silver BETA on GB. These will not start at all and need to be hand patched for real HW support.

[Hiccup]

Nintendo release carts with these bad checksums on them - its not an error produced while dumping them. The consoles just ignore these checksums - I think they are probably just for internal usage by Nintendo, and they don't always remember to keep them up-to-date with the current ROM contents.

[KingMike]

Depends on the console. Almost every console does not care about bad checksums at all. Many beta ROMs would have big problems though.
Bigger flaws are there if you have a ROM which is released with a bad header.
Like Pokemon Gold/Silver BETA on GB. These will not start at all and need to be hand patched for real HW support.

Technically, the GB/GBC boot ROM only cares about the HEADER checksum. (that all the checked bytes in the header sum to 0)

[rwebster]

Would I be better off running my ROMs that have bad checksums through a checksum fixer anyway? I play on my Wii using emulators, but some handheld ROMs on my DSi.

[dreimer]

Both ways are in official VC titles well known for bad checksum ROMs. So it's still of no use.

[Screwtape]

There's a couple of good reasons to use a checksum fixer:

- you're a game developer in the 1990s and the console manufacturer demands a correct checksum in the final ROM image submitted for manufacturing
- you're a homebrew developer and you're worried that some players' emulators might display a warning if the internal checksum is wrong
- you're playing a game you know is clean, but the author released it with a bad checksum, and your emulator complains about it, and it's annoying you

Otherwise, there's no real point. The hash algorithms that No-Intro uses to identify ROM images (SHA2, SHA1, MD5, even CRC32) are much better at detecting data corruption than the internal checksum, so it's generally better to have a ROM image with a broken checksum that matches the No-Intro database, than to have an image with a fixed checksum that's not in No-Intro.

[rwebster]

Thanks for all the info. I'll just keep them as intended then