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Erasing data before selling a computer

How do I wipe my hard drive?

On my iMac that I had, it had a process where it met some government standard in terms of safety by going over the drive 7 times.

marked as duplicate by BinaryMisfit Oct 15 '09 at 12:17

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  • 6
    Who are you trying to protect from? Your grandmother? A script kiddie? The NSA? Formatting the drive will stop the average grandmother, but I'd recommend total destruction to foil the NSA. I can't offer a suggestion without knowing the threat level. – David Thornley Oct 8 '09 at 18:06
  • See this question: superuser.com/questions/4678/… – Josh Hunt Oct 9 '09 at 12:43


Darik's Boot and Nuke ("DBAN") is a self-contained boot disk that securely wipes the hard disks of most computers. DBAN will automatically and completely delete the contents of any hard disk that it can detect, which makes it an appropriate utility for bulk or emergency data destruction.

  • 4
    +1 for DBAN, I suggest Quick Erase, or DoD Short if you're paranoid, or Gutmann if you're actually paranoid. See: Overwriting Hard Drive Data: The Great Wiping Controversy, also Can Intelligence Agencies Read Overwritten Data? – Tyler Oct 8 '09 at 17:44
  • Gutmann himself has stated that his wiping algorithm is completely pointless on today's disks. DoD or even a few random passes is enough. – grawity Oct 8 '09 at 18:05
  • @grawity: Which is not good enough for the truly paranoid, who worry about what the NSA might be able to recover in twenty years or so. For some applications, this level of paranoia is appropriate, but I doubt this is one of them. – David Thornley Oct 9 '09 at 13:53

If you want to make the drive unrecoverable, I think your best bet is to remove the platters and take a belt sander (or sand blaster) to them. By ripping off the magnetic coating, you'll insure that nothing can ever be recovered. Obviously, doing so makes the drive useless, but for maximum protection, you can't beat destroying the magnetic media.

Another approach would be to use a heat gun (or blow torch) and a putty knife to scrape the magnetic coating off. This is bad because who knows what the fumes will contain, but you won't have a load of who-knows-what dust around the workshop.

Another approach would be dropping the platters in an appropriate acid, but I'm not enough of a chemist to know which one would work best.

I don't think much of the drill method proposed by another poster - it only destroys part of the surface, making recovery of only some of the data impossible.

If your objective here is to remove any possibility of recovery EVER, then you really need to attack ALL of the magnetic media on the entire surface. Anything you can do that turns the magnetic media into particulate matter is going to be sufficient.

Of course, as far as we know, no one's ever recovered data from a drive after it's been over-written with zeros. So, it really just depends on how paranoid you are.

  • It is possible to recover data from a formatted drive - it really depends on how much money and time you're willing to spend on it. There is a residual magnetic trace, which you can recover by repeatedly scanning a drive. – alimack Feb 23 '10 at 9:23
  • Assuming that you're talking about a complete over-write of the drive, then in theory this is true, but so far no one's ever actually done it. You'd need some rather specialized hardware (no, you can't pull this trick with the drive's existing controller), and so far no one (including data recovery companies) has ever demonstrated this trick in the real world. Of course, if you completely destroy the magnetic media like I suggested, then you don't have this problem. – Michael Kohne Feb 23 '10 at 23:21

You can also check out File Shredder, a free Windows utility to delete files securely.


You could use a Linux Live-CD and dd together with /dev/null and/or /dev/random:

dd if=/dev/random of=/dev/sda bs=1M
  • It works really well with cp too, see Wiki article about dd (Unix). The effect is perfect, you don't need to do it twice. – guerda Oct 15 '09 at 11:41

If you want it completely non-retrievable, get a drill and bore holes in the thing. As well as leaving holes, it warps the drive platters and makes retrieval impossible.

  • Assume he wants to erase it and resell / donate the hard drive. – Josh K Oct 8 '09 at 17:48
  • It is still possible to retrieve data from places not touched by the drill, I think. – grawity Oct 8 '09 at 18:04
  • New hard drives aren't all that expensive. Older ones are smaller and (being electromechanical devices with lots of sue) less reliable. I don't know that it's worth much effort to securely delete it without destroying it. – David Thornley Oct 8 '09 at 18:04
  • 4
    No! Soak it in acid overnight, rinse it, soak it in gasoline, set it on fire, then grind up the ashes into tiny bits, rinse them again, run them through a strong magnet, and scatter them, one grain at a time, from an airplane flying over the jungle. – Nathan Long Oct 9 '09 at 12:04
  • 2
    Just one jungle? That's asking for trouble... – MartW Oct 9 '09 at 12:45

See Sanitizing hard drives at the hardware level. The tool it links to is DOS-based and may or may not work on an Intel Mac, but you might be able to find a similar tool which is designed for Mac. If not, you can always plug the drive into a PC.

Its advantage over programs like DBAN is that it uses an ATA command built into all modern hard drives which gets the job done quicker and more securely than any software can.

After wiping the drive, recycle it if you can rather than discarding. In Australia there's Byteback for (free) recycling of computer parts.


Just perform a full format (no quick formats here!) on it. Unless you're a government official who stores nuclear launch codes, it'll be enough to stop recovery.

The way file recovery programs work is scanning the disk for data that looks like a file - it can't find it because it's place in the file table is missing. A quick format just wipes the file table, whereas a full format fills the hard drive with zeros. A "secure" format fills the hard drive with zeros. Several times. More secure? Yes. Necessary? Not for most of us.

Of course, it feels really, really good to do it, so I recommend Boot and nuke.

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