Fixing logical bad sectors on floppy disks

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Fixing logical bad sectors on floppy disks

Postby zetatron2000 » 2017-11-30 @ 20:23

Hello guys, I have found a bunch of 3,5" diskettes in my parents home. I formatted them and found out that unfortunately most of them had bad sectors.
But when I tried to do full format on Windows95, some of them had their number of bad sectors decreased.
So I took some and formatted them multiple times, and for some it actually fixed all bad sectors.

My thought is that maybe since the data was in one area for so many years, that part of diskette was so magnetized that windows treated that as bad sector, and that
multiple full format demagnetized it?
Can anyone with more technical knowledge confirm my guess?

Another thing is that windows format utility isn't very user friendly when it comes to format tens of floppy disks multiple times.
I wonder if there is some program that work like DBAN I could use - so I can set to do low level format continuously, and after several hours check if bad sectors were fixed or not, and then be sure that this particular one is dead for sure.
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Re: Fixing logical bad sectors on floppy disks

Postby emosun » 2017-11-30 @ 20:26

zetatron2000 wrote:My thought is that maybe since the data was in one area for so many years, that part of diskette was so magnetized that windows treated that as bad sector, and that
multiple full format demagnetized it?
Can anyone with more technical knowledge confirm my guess?


it probably actually LOST its magnetization over the years much like a pendrive does when it has no power for a long time. Course that might be putting it simplistic but essentially lack of use and simple decay cause them to go bad. I guess through a lot of usage and formats you were able to force some life back into them.
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Re: Fixing logical bad sectors on floppy disks

Postby zetatron2000 » 2017-12-01 @ 14:23

emosun wrote:I guess through a lot of usage and formats you were able to force some life back into them.


Actually if they are fixed by using them that's even better. I was looking for a tool, found out windows format program in win10 have /p option to specify number of passes.
I did a quick check but it didn't really seem to make a difference. Then went back to DBAN. I booted it from CD and was using external FDD on USB. This time the disk drive was
correctly displayed so I set 900 passes on format and went to sleep.
The whole process took more than I supposed (around 13h) but surface test show that this diskette is now free of bad sectors :blush:

So now I'm going to use this method on remaining diskettes and decrease the number of formats, hopefully to find the best setting for most common cases.

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Re: Fixing logical bad sectors on floppy disks

Postby FFXIhealer » 2017-12-01 @ 14:27

This shit right here... Maybe I should invest in a box of 3.5" floppies then if it seems like you can restore them via this method. I wouldn't mind setting up a Dos 6.22 system and I'd want a bunch of floppies to help with the work. It still bugs me that my Carmen Sandiego games keep crashing or locking up in Windows's DOS versions.
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Re: Fixing logical bad sectors on floppy disks

Postby zetatron2000 » 2017-12-01 @ 15:24

Please bear in mind that my floppies were bad only because they weren't used for a long time. For sure this will not fix physical bad sectors.
Still one box of 3,5" isn't much of investment so you can try.
I will also update this post later. I feel like 900 formats is overkill, maybe 200-300 is enough, maybe even less?
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Re: Fixing logical bad sectors on floppy disks

Postby jesolo » 2017-12-01 @ 15:50

I guess for this to work, it has to be an "unconditional" format (in DOS terms, with the /U parameter)?
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Re: Fixing logical bad sectors on floppy disks

Postby Jade Falcon » 2017-12-01 @ 15:54

Very interesting. Wonder who long they will hold up. And I wonder if the need for more then one pass is do to the read write heads not being 100% spot on? and the repeated format allowed it to touch all parts of the disk?
I wonder if swapping the head cable so the drive read the disk upside down/backwards help?

Also LS-120 drives far better with reading bad floppy's.


EDIT:
Now I want to give this a try. I;m sure I have a old floppy around.
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Re: Fixing logical bad sectors on floppy disks

Postby zetatron2000 » 2017-12-01 @ 16:40

jesolo wrote:I guess for this to work, it has to be an "unconditional" format (in DOS terms, with the /U parameter)?


There is a difference between DBAN and normal format. Windows format destroy data by overwriting with zeros.
DBAN is a program to "safely" wipe data so it fills the space with random 1 and 0. There are different methods to choose from
DoD, Gutmann, PRNG stream, each with its own "randomness". I chosed PRNG because it does only one pass per round (Gutmann does 35)
so it's easy to set how many times the disk will be wiped. So I wonder maybe it also help that the floppy was filled randomly, not only 0.

After DBAN treatment you only have to format it with DOS or Windows.
I used sformat program only because it is bundled with norton utilities for DOS and I used Norton Disc Doctor from that package to do surface check.
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Re: Fixing logical bad sectors on floppy disks

Postby Joey_sw » 2017-12-01 @ 23:34

your method somewhat remind me of spinrite but for floppies.
-fffuuu
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