Advice about damaged disk

callmejack

I have a floppy disk that has some physical damage (see below).

Any advice on how I could fix that ? would applying some heat (hair dryer?) help ?

SomeGuy

Ah, dents in the cookie.

No, not heat. You will just melt the plastic.

The best that can be done is to place the disk on a flat clean surface, with whatever side the dents stick up on, face up and then use a firm, but not sharp or abrasive, object to press down on them gently. I think I usually just use a q-tip or the q-tip's shaft. The idea is not to "fix" it, but just to improve things a tiny bit.

Then if this is an IBM PC disk - use Trixter's disk2img. Read it in using a drive that is not mounted in a machine, and manually gently fiddle with the head while it is over the bad area. if you are lucky, you might just get a good read.

I've managed to recover a number of disks with dents using that method. Sometimes the dents even flatten out a bit more and become more readable after running through a drive.

callmejack

Good advice, I had forgotten about this tool and was able to recover the content using the /r parameter. What do you mean by « manually gently fiddle with the head while it is over the bad area » ?

SomeGuy

Usually we treat reading a disk as a 2-dimensional process. The disk spins and the head stays in the same place except moving track to track. But when there is damage, especially like this it can become a three dimensional affair. Gently pressing down on the head, raising the head slightly, or pushing slightly forward or backwards on a head can make a difference when reading a marginal sector. That is exactly the sort of thing disk2img was written for, as you can see the results of your "fiddling" in real time to quickly determine if reading is getting better or worse.

callmejack

Very interesting, I would never have dared to touch the head during the reading process. Do you have to be in recovery mode (/r) to do that or normal mode ?

SomeGuy

I'd use normal mode and make sure the number of retries is high enough to give you time to mess with it. Then when it encounters a sector it can't quite read, it will just sit there re-reading it showing you pretty changing garbage, and while it does that you can carefully fiddle around and see what happens.

Please make sure you understand what recovery mode is. It cobbles together whatever bits seem most probable. I've had a number of disks where a single bit is flipped, so it will always re-read the EXACT same bad data, and recovery mode will just assume that is "correct enough". Depending on the content, that may not be a bad thing (text file, empty sector, or such). But recovered does not mean 100% accurate.

callmejack

So in recovery mode it could read a track 60 times and because one same value is read 50 times out of 60 it will assume it’s correct even if crc fails? And normal mode it will try to read it indefinitely until crc matches ?