There is a huge flaw with the fds format.
Important bytes, GAP data and crc checksum, are missing from all existing dumps.
This is a flaw (or intended?) in copiers, conversion utility, or driver softwares. I don't know the details about how these bytes are skipped but this means no perfect dump of a FDS disk will exist as long as a new method to dump the disks properly is conceived.
I just wanted you all to be informed. No FDS dump can be called perfect. And accurate emulation can't be achieved as long as these bytes are missing.
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Re: Famicom Disk System discussion \ Yuki on 31st October 2006, 21:07 wrote:
Is there a title that doesn't operate correctly by FDS?
It is not at all realistic to assume that new Format was made, and to do all ReDump of FDS.
I think that obtaining FDS is difficult if it is not Japan perhaps.
And, it doesn't like to offer it to us though many of Japanese who do Dump boast of the file that does Dump.
I have seen such a lot of Japanese.
Anger to it makes me face a lot of FDSDump.
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Re: Famicom Disk System discussion \ Yakushi~Kabuto on 5th November 2006, 14:13 wrote:
was my post so technical that no one understood it
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Re: Famicom Disk System FDS dumps study \ Yakushi~Kabuto on 4th February 2007, 17:25 wrote:
Here is a little study of the differences in the save area between
-bad dump / used disk
-save cleaned
-good dump / sealed disk
Conclusions
-bad dump / used disk has 13 wrong bytes
-save cleaned has 3 wrong bytes (10 corrected properly)
This little study illustrates perfectly that the No-Intro cleaned dump was more accurate to the good dump than the original bad dump. However, cleaning doesn't make good dumps, and redump is still needed.
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Re: Famicom Disk System FDS dumps study \ Yakushi~Kabuto on 25th March 2007, 15:43 wrote:
It came to my attention that some FDS disks are protected against copy.
Here is how the protection does work from the infos I could gather:
All FDS disks have their own size written on the header.
In the protected FDS disk, the size written on the header is wrong (smaller than it really is).
So when the FDS copier does a backup, it misses a few DUMMY bytes at the end of the disk.
When the disk is loaded, it changes temporarily the header to indicate the correct size. It then scans the disk in an attempt to find the DUMMY data. If it can not be found, then the disk is considered as an illegal copy and it will display an anti-piracy message.
here is the difference between a "normal dump" (missing data) and a "protected dump" (with dummy data included).
However, the problem is the real disk should display a wrong size.
The current FDS copiers are fixing the size in headers, so they are likely HACKED DUMPS.
I'm waiting for a confirmation from some NES devcs, but it is likely all protected disk will need to have their header reverted in the next dat.
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Re: Famicom Disk System FDS dumps study \ Skrybe on 30th May 2007, 18:20 wrote:
I see where a sealed disk redump would be needed for games that save to the disk, but what about games that don't, like most unlicensed disks?
I ask because I have a friend who has a copy of the undumped Disk Keeper program, and an FDS copier. His copy of Disk Keeper isn't new, though, nor is it an original disk. It's a bootleg copy he bought in an auction. Would you accept a dump of that copy as a "good" dump, even though it's not a sealed disk dump?
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Re: Famicom Disk System FDS dumps study \ Yakushi~Kabuto on 30th May 2007, 21:24 wrote:
Unlicencied usually don't write back into the disk AFAIK. So yes we would gladly accept it if it's undumped and documented enough (shots), however its dump status would be "UNCONFIRMED".I see where a sealed disk redump would be needed for games that save to the disk, but what about games that don't, like most unlicensed disks?
I ask because I have a friend who has a copy of the undumped Disk Keeper program, and an FDS copier. His copy of Disk Keeper isn't new, though, nor is it an original disk. It's a bootleg copy he bought in an auction. Would you accept a dump of that copy as a "good" dump, even though it's not a sealed disk dump?
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Re: Famicom Disk System FDS dumps study \ Skrybe on 31st May 2007, 23:49 wrote:
What do you require for a "confirmed" dump, then?
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Re: Famicom Disk System FDS dumps study \ KingHanco on 2nd June 2007, 20:06 wrote:
I will be glad this will be straighten out soon. I just hated to know all those aren't good dumps.
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Re: [Research] Famicom Disk System FDS dumps study \ Tidegear on 19th July 2007, 23:14 wrote:
Is there a way to slip the crc checksum and gap data into an FDS file and still have it be readable by most emulators/programs? Maybe at the end of the file? Or will the FDS format need to be totally restructured requiring emulators/programs to be updated in order to read them?
Automerged Doublepost.
Sorry to bug you here, Yakushi~Kabuto but I think there's something wrong with the PM system. I responded to your PM and it didn't show up in the sent box, nor did I receive any response from you even after a couple days. I tried sending a couple follow-up PMS but they didn't show in my sent box either. I'm hoping you got them and just haven't had time to respond yet. If not is there a better way to reach you about the Knight Move dump?
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Re: [Research] Famicom Disk System FDS dumps study \ Manowar on 24th July 2007, 12:08 wrote:
The work done here on the FDS system is wonderful. I think the FDS is a great system that needs to be documented properly (which it is), along with the great dumping capabilities being put forward here!
