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I would like to make data, in many (more than 250) old floppies, unreadable/unrecoverable.

I have some HDDs that I can take apart. Their magnet is sufficient to do the job to make it unreadable to the general public? How much time it will the process take?

I don't want to destroy the floppy as I want to re-use them (some floppy art).

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    Out of curiosity, have you tried reading the floppies? They suffer from degradation and might be unreadable already. Sigh - my Wasteland saved games .... – schroeder Oct 24 '19 at 8:38
  • @schroeder I don't want to destroy them, I'm going to try to check if they already have gone... but in case they are working? – Kintaro Oct 24 '19 at 8:46
  • I lied; one more: 3.5" or 5.25" floppies? – schroeder Oct 24 '19 at 8:57
  • Is there a specific reason you do not want to just burn the floppies? – Dr_Bunsen Oct 25 '19 at 8:54
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Ideally you need a bulk degausser. Back in the day of cassette tapes you could get a bulk degausser for about $20. Alas, this is now a specialty item and runs around $100.

Using something like a neodymium magnet waved around the surface will selectively damage portions, making it unreadable by normal efforts.

You have to decide the threat level you're concerned with:

  • National Security - Destruction
  • Forensic Labs - Bulk Degauss
  • Curiosity - Magnetic damage
  • You can probably buy a second-hand degausser off Ebay for $5. – Mark Oct 24 '19 at 20:57
  • @Mark I searched for it (in Italy) and the cost is much more, and for the threat level I'm facing, is not worth it. – Kintaro Oct 28 '19 at 7:34
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Yes, a HDD magnet is fine or any neodymium one and will destroy the data by sweeping such a powerful magnet across the surface of a disk. However, the reliability of such a procedure may vary.

You can also build your eraser in a similar manner to making a head demagnetizer for tapes (which is pretty simple: insulated wire, nail and an input voltage source).

If you erase your floppy disk (completely or partially) using a magnet, the track sector markers are destroyed. A quick format won't find them and therefore the format and/or any write to the disk will fail. A normal format may also fail due to not finding 1st sector marker information. However, special MS-DOS era programs may be able to re-format the disk and rebuild all track sector markers, therefore making the disk reusable.

  • a re-format can make them reusable and "old data" recoverable? – Kintaro Oct 24 '19 at 9:14
  • @Kintaro reformating may be able to find some datas. You can recover a lot with physic oriented forensic analysis. But the time, money and effort needed for that should be enough to discourage someone from doing that on your floppies – Deunis Oct 24 '19 at 9:19
  • @Deunis with floppies, you can use a hex editor to read sectors even after formatting. – schroeder Oct 24 '19 at 9:33
  • Not after a true classic formatting. Quick format is not a format, it's a general pseudo-cleanup. I mean a HEX won't work. Deep forensics are another matter, but it also can be taken care of. On FD times we used to have low level format even for HDD. – Overmind Oct 24 '19 at 12:47
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I played with floppies and magnets in the 80's and a simple fridge magnet could render a floppy unusable. I did not perform a forensic analysis to determine how much data could be recovered, though.

HDD magnets are very powerful for their size. But the trick is not the size or strength of the magnet but motion. Wiping the magnet across the entire surface, even once, had better results (less likely to be read when loaded and more corrupted files). Twice was even better.

All this is anecdotal evidence, though. To be sure, you would need to pop the "wiped" floppy in a drive to check it out.

  • If the goal is to remove all chances of the data ever being recovered, why not cut the magnetic part off and light it on fire? That's a serious remark, not a joke. – MechMK1 Oct 24 '19 at 9:46
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    How do you do that without damaging the floppy? – schroeder Oct 24 '19 at 9:51
  • The entire idea is to irrecoverably destroy it. – MechMK1 Oct 24 '19 at 10:04
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    ... with the condition of keeping the floppy in tact ... – schroeder Oct 24 '19 at 10:06
  • ...and without taking ages! – Kintaro Oct 24 '19 at 10:31

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