TransCopy vs. Original

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PolymorphedDragon
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TransCopy vs. Original

Post by PolymorphedDragon » Sat Apr 25, 2015 2:27 pm

I've got a few disks here made on a modified drive that could write to notchless disks, but they're showing up good on my KryoFlux. Is there any way to detect these duplicates?

Edit: not all of the duplicates show up as unmodified. Some are showing entirely modified as expected.

ibmpc5150
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Re: TransCopy vs. Original

Post by ibmpc5150 » Sat Apr 25, 2015 5:27 pm

I want to know which program or game disk for.

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IFW
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Re: TransCopy vs. Original

Post by IFW » Sat Apr 25, 2015 6:38 pm

As long as the tracks on the copy are written in a single pass, they will show as unmodified.
A track is modified if any of the sectors has been re-written since duplication or formatting - both duplication and formatting writes track at once.

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IFW
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Re: TransCopy vs. Original

Post by IFW » Sat Apr 25, 2015 6:42 pm

It is also usually possible to detect the copy even if the track is written at once, but it requires more complex investigation and the method depends on the target platform (actually the limitations of the target platform).

NRS
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Re: TransCopy vs. Original

Post by NRS » Sat Apr 25, 2015 8:02 pm

As I understand it, PC disks can be detected as "modified" if there is something other than 0x4E in the gap between sectors, or if the MFM framing changes from address mark to address mark. Both of which will occur with sector-by-sector writing by a normal PC floppy drive. Protections that deliberately put data in inter-sector gaps (i.e. Softguard Superlok on the PC) will erroneously lead to a disk being labelled "modified". Since Transcopy writes a track at once, disks written that way will not be detected as a copy by this method, unless the master disk had already been written to at the time the Transcopy image was made from it.

Another method could be to look for slight speed varations in the flux change stream, assuming that a professional duplicator provides more steady timing than normal drive. Although I wonder how one could tell whether a "jittery" flux stream is that way because of speed variations during writing, or because of speed variations by the drive dumping the disk with the Kryoflux or equivalent device! I also wonder whether professionally duplicated disks really are always much more stable in the timing of their flux reversals, especially if they were mastered at higher than normal speeds. For example, the Formaster Series One allows mastering at 600 rpm.

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IFW
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Re: TransCopy vs. Original

Post by IFW » Sun Apr 26, 2015 6:35 pm

Yes, most professionally duplicated disks are way better quality than user disks, mostly thanks to advanced pre-compensation used - compared to what you get with a stock MFM controller.

DTC checks for modifications in both the data and the time domain, but it does not care about 4e values or anything similar in data domain, it's a lot more complex.

NRS
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Re: TransCopy vs. Original

Post by NRS » Sun Apr 26, 2015 7:56 pm

Well, that was delightfully nondescript.

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mr.vince
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Re: TransCopy vs. Original

Post by mr.vince » Sun Apr 26, 2015 8:25 pm

Maybe because that is part of our pro services and tools which help finance further development. Without such pro sales and e.g. forensic / data recovery assignments KryoFlux could not do what it does feature-wise.

You would not give away the family stew receipe either, right?! ;)

NRS
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Re: TransCopy vs. Original

Post by NRS » Sun Apr 26, 2015 10:04 pm

I'm not complaining, just stating my... delight. ;)

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mr.vince
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Re: TransCopy vs. Original

Post by mr.vince » Mon Apr 27, 2015 7:22 pm

You're in good company with delight; haven't gotten complaints so far. ;)

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