03-12-2016, 06:45 AM
(03-11-2016, 09:45 AM)admin Wrote: OK, I scanned both disk images with several Amiga copy programs, and even copied the disks just fine. There are no read/write errors in the images (because that is not possible). However, the problem you see (that shows a read/write error when it is actually not) has to do with the fact that file link data is invalid. It looks like this is a case where it just so happens that the Amiga sector data checksum'd correctly. The Amiga's checksum technique is not the most robust, so it's possible that you can have invalid data checksum correctly. The checksum is the only thing we have to go by for determining if the data is really good or not. This is the first time I have seen this since back in the 90's when I had a disk do the same thing.
Hey Thanks for putting in your time.
The disks are old, badly kept and have visible dirt spots on the surface. After I clean them with a alcohol/detergent solution they are still barely readable. So I guess this is a situation where the check-sum is put to a test like never before.
I also found out that X-copy and the likes are not showing errors at all. They copy even the most miserable images just fine, but the copy is broken. I looked for a chkdsk equivalent on Amiga OS, but it doesn't exist besides maybe Disksalv, which isn't what I need. I check if the disk is fine by doing a DOS copy to RAM (or HD for keeping), file by file.
I didn't notice any corruption in data files though (yet). If the check-sum was prone to so many mistakes, I guess it should show up there as well?
I'm trying to make sense of the ADF format and sector layout of Amiga disks so I can change things in a HEX editor, but I'm not quite there yet. ;-)