What system were they from? That might be helpful to list readers (or yield someone with a working system that can read them "natively")
The first cylinder is normal, but after that, the next 21 cylinders don't even have a sector 0.
If the discs were formatted with a WD17xx series controller, it's possible that the first sector is too close to the index hole for the PC's floppy controller to detect.
http://z80cpu.eu/archive/news/comp.os.cpm/threads/49581d115e7ce5d6.html http://simonowen.com/samdisk/faq/
In article E1PdUCJ-0004Rh-63@beholder, John Elliott wrote:
If the discs were formatted with a WD17xx series controller, it's possible that the first sector is too close to the index hole for the PC's floppy controller to detect.
Yes, that was my thought. However, the s/w I'm using (cw2dmk) can be told to ignore the index hole and the data is no better in this mode. I'm guessing the data was dodgy when written 20+years ago, though why it's just the first sector after a track change I can only guess at. Write affected by head stepping? Who knows!
Anyway, I can now get low, real low, magnetic domain transitions on the disk low, which makes me happy. I've captured the data off all eight disks with a variety of settings and can now start writing code to parse the data. I reckon that over 99% of the data is present and correct, and another 0.9% will be there with good CRCs even if the headers are mangled. The remaining 0.1% will be "interesting".
Ian
In article VA.0000291c.0b45b9a8@foxhill.co.uk, Ian Oliver wrote:
I reckon that over 99% of the data is present and correct, and another 0.9% will be there with good CRCs even if the headers are mangled. The remaining 0.1% will be "interesting".
OK, I just wrote 200 lines of skanky Python that does basic parsing of a DMK file, finds the id and data for every sector, runs the checksums, and writes out good data.
Despite the grim ids (some missing, those for sector 1 of head 0 for the first 34 sectors having the right checksum but wrong track number!) the data checksums were pretty much all good. However, whatever caused the ids to be wrong has clearly scambled the data. It won't restore and the mk1 eyeball suggests that one sector per track (oddly sector 15!) has duff data despite the good checksums.
All those 20 years ago, our backup software was clearly having a bad day when it wrote those disks. I've done what I can and can do no more.
Ian
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Ian Oliver -
John Elliott