How should I erase my hard drive before I give it away?

Not an option: Leaving anything

Quite often, I get this question with an additional caveat - how to remove all of your personal information while leaving Windows installed.

You can't.

The problem is that even after removing all of your data - even if you remember to remove every scrap and even after removing every single application - some of your personal information will still be left on the machine.

If nothing else, there's likely to be random information left in the Windows registry, and unless you take additional steps, all of those files that you carefully deleted could potentially be recovered.

What's worse, of course, are the people that do nothing and leave everything on the machine. It's not uncommon to hear stories of second-hand machines containing a wealth of personal and private information from the previous user.

Let's not do that.

Basic precaution: Format the drive

Conventional wisdom is that reformatting your disk is the right thing to do. And I agree with that, if done properly.

What do I mean by "properly"?

Windows (all versions), and even MS-DOS before it, have the option to perform what's called a "quick format". In reality, a quick format does very little except create an empty root directory on the hard disk and possibly add a label. The rest of the disk is actually assumed to be properly formatted already and left alone. That's why it's quick.

And that's why it's also insecure. Because the rest of the disk is left untouched, any data that is already there will remain. Many commonly available disk recovery tools will be able to recover data from a "quick" formatted disk.

So the basic and common answer is to reformat the disk, making sure to specify unconditional format.

Unfortunately, if that's your C: drive, you won't be able to format the drive if you've booted from it and are running Windows from it. You'll need to either install the disk in a different machine to be able to reformat it or boot from something else.

For the later, I have just the thing...

A safe, practical approach: DBAN

DBAN, which stands for "Darik's Boot And Nuke", is a free utility designed to do exactly what we're talking about by living up to its name: it's a CD that you boot from that then "nukes" the information on the drive.

Download the DBAN CD image, burn it to a CD, and then boot from the CD. I need to be really clear on what happens next:

DBAN will automatically and completely delete the contents of any hard disk that it detects.

DBAN does this not by simply deleting files, but by performing a careful overwrite of the entire hard disk surface. When it's done, everything is erased.

Everything.

In fact, DBAN has options to overwrite/erase the hard disk multiple times, so as to prevent any possibility of future data recovery.

DBAN is now my recommendation when you're about to dispose of a hard disk or give a computer away.

Over the top: Physical destruction

It's a common recommendation to use a big heavy magnet to really erase a hard disk. My advice is to forget it. Any magnets that you're likely to have around the house, even your big speaker magnets, are unlikely to affect your hard disk in any significant way. I believe that there have been studies that show that even some exceptionally large magnets still leave the contents of hard disks in a recoverable state.

Another approach to really, positively, and permanently destroy your data is to physically destroy the disk.

Personally, DBAN is more than enough for me, but if I care enough to go this far, I use a drill press and drill a few holes all the way through the hard drive casing, through the disk platters, and out the other side.

Unfortunately, that level of destruction also makes your gift significantly less useful.

If you want to leave Windows on the machine...

As I said before, it's common to want to leave Windows installed as part of your gift.

That may or may not be legal (it depends on the terms of the license for your particular copy of Windows). To keep it at least ethical, it means you would no longer keep or use that copy of Windows yourself.

The right and safe way to transfer Windows in this case is to, after running DBAN, reinstall Windows from scratch using your original installation media. If your system didn't come with installation media, then you could try the restore media that you received or you could restore to an image backup that you took immediately after receiving the machine.

And part of your gift would be to include the product key that activated that copy of Windows.

A product key that, as I said, you would no longer use yourself, having given it away.

(This is an update to an article originally published December 24, 2004.)