11 Replies - 979 Views - Last Post: 28 January 2012 - 07:26 PM

#1 Sinned  Icon User is offline

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Completely harddisk erase

Posted 25 January 2012 - 07:51 AM

Hello everyone,

I was wondering about all those tools on the internet which are made to completely erase files from the harddisk.

Those programs could do 1 pass, or also more passes (like 35).
Why is this needed? When a bit on the disk is set to zero, why do it again on a new pass?

Also was I wondering why simple Linux commands aren't good enough to erase data, like:
dd if=/dev/zero of=/dev/sda bs=1M

This also completely erase all data, by setting each bit to zero. right?

So I should like to hear your opinion, counterargument or response on this.

Thanks,

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Replies To: Completely harddisk erase

#2 modi123_1  Icon User is online

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Re: Completely harddisk erase

Posted 25 January 2012 - 07:55 AM

In really old hard drives it was still possible to read the previous state even when over written.. this is less true with newer hard drives, but if you ass is in a sling with medical records, corporate docs, or government secrets it's better to be sure than sorry.
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#3 Lemur  Icon User is offline

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Re: Completely harddisk erase

Posted 25 January 2012 - 07:56 AM

Things aren't immediately erased, they're moved to a trash segment for pending overwrite later. This was made because some people haphazardly deleted files that were considered fairly important, so OSs took to making this the default. It does far more good than harm.
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#4 Sinned  Icon User is offline

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Re: Completely harddisk erase

Posted 25 January 2012 - 08:14 AM

View Postmodi123_1, on 25 January 2012 - 07:55 AM, said:

In really old hard drives it was still possible to read the previous state even when over written.. this is less true with newer hard drives, but if you ass is in a sling with medical records, corporate docs, or government secrets it's better to be sure than sorry.

I didn't know it was possible with old hard drives to see the previous state.
Thanks

View PostLemur, on 25 January 2012 - 07:56 AM, said:

Things aren't immediately erased, they're moved to a trash segment for pending overwrite later. This was made because some people haphazardly deleted files that were considered fairly important, so OSs took to making this the default. It does far more good than harm.

That wasn't my question.
I knew this is happening, but I was asking for the step to completely erase the data.
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#5 Toadill  Icon User is offline

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Re: Completely harddisk erase

Posted 25 January 2012 - 09:58 AM

I believe this would fall under the category of a low level language, such as ASM.
Although it is also possible to write a driver in a higher level language like C++

Maybe you could use a windows API or even use the DOS interrupter to format the hard drive.

Win32_DiskPartition Class

Win32_LogicalDisk Class
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#6 Lemur  Icon User is offline

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Re: Completely harddisk erase

Posted 25 January 2012 - 11:55 AM

Just stick a nice powered magnet on it. Problem solved. Now if you want a complete disk shred, find a live distro that provides such a tool. Normally 5-6 low level formats clean every inch of it.
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#7 calvinthedestroyer  Icon User is offline

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Re: Completely harddisk erase

Posted 26 January 2012 - 09:11 AM

You want to read up on data recovery method's.

basically your hard drives head does not always write in the same path, it verys back and forth by thousands of an inch (maybe even less than that). The path that the new data makes as it writes over the old data path is slightly off, leaving behind a sliver of old data. You can remove your hard drive platters and then install them in a fixture with very tiny hard drive heads. These tiny-er heads can read the old data on the sides of the new data path.

Here's and example.

drive your car through dirt and make some tire marks. Now drive back over your tire marks. Get out and look at the marks/paths, Did you completely cover up the old tire marks/paths?
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#8 Gorian  Icon User is offline

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Re: Completely harddisk erase

Posted 27 January 2012 - 08:04 AM

man, can't believe no one has suggested DBAN yet.
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#9 Kilorn  Icon User is offline

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Re: Completely harddisk erase

Posted 27 January 2012 - 08:13 AM

View PostLemur, on 25 January 2012 - 02:55 PM, said:

Just stick a nice powered magnet on it. Problem solved.


This is actually a common misconception. Next time you have an electromagnet handy, boot up a computer while the hard drive is exposed and place the magnet directly on the drive and turn it on. The computer will freeze for the period that the magnet is on the drive because the drive will stop spinning. Once you remove the magnet, the drive will continue spinning where it left off, and the computer will resume functioning. We do it here at work on a regular basis because it's fun and we get bored from time to time.
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#10 no2pencil  Icon User is offline

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Re: Completely harddisk erase

Posted 27 January 2012 - 09:09 AM

View PostKilorn, on 27 January 2012 - 10:13 AM, said:

View PostLemur, on 25 January 2012 - 02:55 PM, said:

Just stick a nice powered magnet on it. Problem solved.


Next time you have an electromagnet handy, boot up a computer while the hard drive is exposed and place the magnet directly on the drive and turn it on.

I have plans to do this on my friends youtube channel. People freak out when I use magnetic screwdrivers, & it's like, hey, you want me to lose a screw in your system? The rare-earth magnets that are already installed inside the hard drive are way more powerful than anything my screwdrivers are introducing.

View PostGorian, on 27 January 2012 - 10:04 AM, said:

man, can't believe no one has suggested DBAN yet.

I clicked on reply to do just that :P

View PostToadill, on 25 January 2012 - 11:58 AM, said:

I believe this would fall under the category of a low level language, such as ASM.
Although it is also possible to write a driver in a higher level language like C++

Erm, how does language dictate hardware?

Sending requests to the file system in assembly creates no different binary than if you do it in C/C++.

I once had a guy tell me that Microsoft writes everything in assembler to make more difficult to be hacked. A binary executable is the same regardless of what language you write it in. Assembling or compiling, your creating a binary executable that performs whatever instructions you gave it. Assembler is not some magic key that opens doors you didn't already have access to.
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#11 no2pencil  Icon User is offline

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Re: Completely harddisk erase

Posted 27 January 2012 - 09:15 AM

View PostSinned, on 25 January 2012 - 09:51 AM, said:

Also was I wondering why simple Linux commands aren't good enough to erase data, like:
dd if=/dev/zero of=/dev/sda bs=1M

This also completely erase all data, by setting each bit to zero. right?

If doing it once is good, doing it twice is great. Just swap the zero to a one, & you'll defeat most conventional recovery methods. DBAN is still the most preferred method.
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#12 calvinthedestroyer  Icon User is offline

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Re: Completely harddisk erase

Posted 28 January 2012 - 07:26 PM

This is how you erase a hard drive:

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