Re: deleting a hard drive
From: David H. Lipman (DLipman~nospam~_at_Verizon.Net)
Date: Wed, 15 Sep 2004 22:22:00 GMT
Sure, I never inferred for SECRET and above data, just SBU data.
In my original reply, I stated degaussing.
"Moe Trin" <email@example.com> wrote in message
| In article <wOJ1d.4214$F75.3528@trndny01>, David H. Lipman wrote:
| >I trust the US DoD's new methodology.
| I'm not sure I would.
| >It basically describes writing a pattern such as 01010101 the writing its
| >complement 10101010
| The fallacy is that this assumes the ancient FM encoding scheme from the
| 1970s - and NO disk has used that scheme in _decades_ Modern hard disks
| use RLL 2,7 encoding, that takes groups of two, three and four bits and
| encodes them into four, six, or eight POSSIBLE flux transitions. The
| scheme is:
| DATA MAGNETIC CHANGE DATA MAGNETIC CHANGE
| 10 NTNN 11 TNNN
| 000 NNNTNN 010 TNNTNN
| 011 NNTNNN 0010 NNTNNTNN
| 0011 NNNNTNNN
| Thus, the '01010101' bit pattern is encoded on the disk as:
| 010 10 10 10 10 10 10 10 10
| TNNTNN NTNN NTNN NTNN NTNN NTNN NTNN NTNN NTNN
| while the '10101010' bit pattern is encoded on the disk as:
| 10 10 10 10 10 10 10 10 10
| NTNN NTNN NTNN NTNN NTNN NTNN NTNN NTNN NTNN
| Now, removing the spaces I put in here so that you can see the transition
| patterns, you get:
| You should be viewing this in a fixed width font on your news tool. But
| this shows that the complementary data pattern does NOT result in a
| complementary pattern ON THE PLATTER. Here, I show an X where the data
| changes from 'transition' to 'no transition' (or vice versa), and a dash
| where there is no change.
| So, half the magnetic domains are unchanged. Note that if you were to
| map the domains (North verses South), this is only s _SHIFT_ of where
| the changes occur.
| >then another patter such as 11001100 and repeating this six times.
| 11 0011 0011 0011 0011 0011 0011
| TNNN NNNNTNNN NNNNTNNN NNNNTNNN NNNNTNNN NNNNTNNN NNNNTNNN
| 0011 0011 0011 0011 0011 0011 0011
| NNNNTNNN NNNNTNNN NNNNTNNN NNNNTNNN NNNNTNNN NNNNTNNN NNNNTNNN
| Now you may have a clue as to why this is for "Unclassified DoD Computer
| Hard Drives" only. I repeat. If you are going to store stuff on a disk
| that you don't want anyone to see, YOU MUST DESTROY THE PLATTERS TO
| PREVENT ANY POSSIBLE DATA RECOVERY.
| Old guy