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I can think of several ways you could "erase" the data on a hard drive:
1. Delete all the files. (E.g., delete C:\*.*)
2. Format every partition with, say, NTFS.
3. Delete all partitions.
4. Low-level format the drive (using, e.g., Maxtor PowerMax).
5. Write zeros to every byte. (E.g., dd if=/dev/zero of=/dev/sda)
6. Write random data to every byte. (...of=/dev/urandom)
7. Physically disassemble the drive, seperate the platters, magnetise
them, scratch them, smash them to pieces, and melt the pieces in a vat
of heated acid.
As I understand it, option #1 is fairly easy to reverse. (Especially if
you just delete all the files and then throw away the disk. All file
data is guaranteed to still be there, you just have to find it somehow.)
Option #2 destroys some of the filesystem metadata, but AFAIK the blocks
holding file data will still be intact. (Formatting with, say, ext2
takes a tiny fraction of the time that FAT or NTFS formatting takes, so
I'm assuming that NTFS overwrites more data. But I don't *think* it
overwrites everything.)
Option #3 should be pretty simple to reverse, AFAIK.
I am unsure as to whether #4 and #5 are different in any way. Both seem
to take the same amount of time...
As far as I know, both option #5 and option #6 make it impossible to
read any useful data from the drive just by plugging it in and asking
the drive electronics to read the data off the disk surface. In either
case, you would have to physically dismantle the drive and crawl over it
with a microscope - which is damned expensive. Using random data (and
multiple passes of it) reputedly makes this process harder - but not
impossible. Non-sequential writes are supposed to make it harder still.
As far as I can tell, option #7 gives 100% guaranteed data destruction.
But I don't have any star-drive screwdrivers. :-P [Or heated acid -
unless you count my stomach. And I am *not* putting shards of shattered
glass in there!]
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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