Unknown floppies

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Joined: Wed Jan 23, 2019 8:24 pm

Unknown floppies

Post by mikjaer »


I'm working on an old system, it's a cp/m 3.0 based system using 3.5" DD floppies, I can copy them using imagedisk. But some of them produces read-errors, and I would like to try to read them with kryoflux … how do I proceeed ? What do I need to do?
Posts: 297
Joined: Wed Feb 18, 2015 8:18 pm

Re: Unknown floppies

Post by SomeGuy »

First of all, visually inspect the disk surfaces and clean any dirt or grime with a q-tip and water. Only consider alcohol if you don't see any oxide shedding.

Dump the floppy disk using a preservation stream file.

Always keep the first dump, as the disk may deteriorate as it is used.

Then go back and decode the stream file. Different tools use different processing algorithms and may have better or worse luck decoding a bad track. Normally, I test decoding in Kryoflux, HxC, and the PCE emulator disk tools. HxC and PCE tend to be more forgiving of noise than the Kryoflux.

With the Kryoflux, you can go back and retry reading individual tracks. If nothing succeeds at decoding a track, you can re-read that track, replace the RAW file in the previous dump, and try decoding again.

You may also wish to try different floppy drives. Minor variations in electronics, head alignment, and so on, can have drastically different effects when reading marginal sectors.

A preservation stream keeps all possible parts of a track. This can aid recovery later when only a small part is permanently unreadable. Sometimes manual pattern matching, and comparing against sector CRCs can repair the data. That, however, is a very involved process.

You can post preservation streams here for others to look at if advice on a specific disk is needed.
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