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by foresto 142 days ago
> I was able to replicate that protection mechanism just by scratching a diskette with a pin.

How did you figure out where to scratch it? Was the laser mark visible on the original disk, or did you have to read the code and orient based on the diskette's index hole?
2 comments
anyfoo 142 days ago
Yes, it was apparently very visible: https://martypc.blogspot.com/2024/09/pc-floppy-copy-protecti...

But as I mentioned in a sibling comment, I’m not sure it was ever confirmed that it was really a laser that made that mark.

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antonvs 142 days ago
I described two different scenarios: defeating the protection, and replicating it, e.g. to protect your own software without paying Vault for their "laser" protection.

Defeating the protection didn't involve knowing anything about the laser mark - as the comment I replied to described, it just involved changing a conditional jump to an unconditional one.

Replicating the protection involved causing minor damage on the diskette - the details don't really matter, laser, pin scratch, whatever - then formatting the disk, and registering the pattern of bad sectors created by the damage. A normal copy of the disk didn't replicate those bad sectors exactly, which made it possible to detect that the original disk was not present.

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lstodd 141 days ago
Ha! I remember disk copy programs which read these bad sector patterns and then replicated the error pattern in software (not on physical disk obviously).

Similar stuff was later used for CDs IIRC.

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