Hard disk wiping - single vs multi-pass

I worked in a decom department for a while, wiping hard drives... but I never knew the difference between a single pass wipe, or a 3 or 7 pass one. I know the disk is written multiple times to ensure that all the data is gone, but what's the point in more than one pass? Surely if a drive has been completely written with 00's, nothing is recoverable... what are the benefits of doing this multiple times?

No, there is a certain degree of residual magnetic flux even after the entire disk has been overwritten with 0s, 1s or even randomly, which means data can be recovered with the right software/know-how. Ever had a cassette tape where you recorded over something, but can still faintly hear the old recording during the silent parts? This is much the same thing (only digital data, not analogue). Multiple passes weaken the "residue" until eventually it's virtually indecipherable.

Good answer. Thank you sir.

Multiple passes weaken the "residue" until eventually it's virtually indecipherable.

Technically, you can't ever completely wipe a disk. Old data tends to slowly bleed into the area between tracks, so even if you wipe several dozen times, the new data hasn't been there long enough to wipe what's between tracks. So long as you don't wait too long, the old data is still accessible by some (amazingly expensive) lab techniques.

The only way to guarantee unreadability is to destroy the disks. For higher levels of classification, DoD resorts to pulverizing and melting old disks.

I know that's what >>2 meant by "virtually", but I just wanted to clarify for any readers. As long as the disk exists, someone can read old data off it. The question is whether it's worth it for them to do so.

>>1 completely written with 00's

I'm no wiping major but I believe it is much easier to find data within "NOTHINGHERENOTHINGHERE" than "JKLLjdlakjdlaskasjld."

Zero-wipes are fairly low on the safe scale. The highest safety is in 30+-pass random, though there are specialized patterns for certain data and drive-types. The whole thing is really not viable for a criminal because it takes so long and is so flawed. As the above said the best bet is destruction, but beware that even that leaves remnants.

If someone has enough money and enough manpower you're probably fucked regardless unless it's melted. That or encrypt the data before writing it, so without the encryption it's garbage.

|Old data tends to slowly bleed into the area between tracks

That's getting less of an issue now that the magnetic domains are getting packed closer and closer together. I wonder how perpendicular recording affects this situation? The whole point of perpendicular recording is to move the magnetic domains closer together (increasing areal density) while preventing cross-contamination of bits.

I seriously doubt anyone here is important enough to need anything more than a 2 or 3 pass wipe with random data.

>>4
Yep.  Melting will do the job, but for us poor-folk on the coast we poke holes in the drive case and use them as weights in crabpots.  The corrosion from the dissimilar metals is impressive.
>>7
If not me, then who?  Does not every internet prole deserve the same privacy in their persons and papers as Party Members?

>>7
You do not have to be doing something illegal for your computer to be confiscated. As 4chan users we are some of the most vulnerable to it.

Some people value their newfound privacy and rights, some think it's a waste of time. A nifty fact to remember is that the police can call up the FBI pretty much whenever they want, so don't act like dumb local cops will be stopped by just a 3-pass. Of course, this shit is the least of your worries with things like Carnivore.

LOLING at the lolis & pedos who have to worry about such shit!!

This thread has been informative.  Thanks Anonymous.

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