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DADDY BOB'S COMPUTER Q & A
September 7,
2008
Q.
I have an old Aptiva PC that is not use
anymore and would like to give it to an
organization that refurbishes old ones and
gives them to kids that would like to have
one but can't afford it. Where can I get a
program that would erase all of my
information that is still on the PC?
A.
To completely wipe the hard drive
clean, you cannot just delete everything on
it. Contrary to common belief, when a file
is deleted from a computer it is not really
deleted. A little explanation is needed
here.
When the
hard drive is formatted, it is divided into
tracks and these tracks are divided into
sectors. For more information on this,
take a look at my article on
Hard Drive
Fragmentation in the Articles
section on this site. These sectors are
grouped into clusters and these clusters
become the allocation units. When a file is
to be saved, its size is calculated, and the
required number of clusters needed to hold
it are allocated, and marked as "In Use".
Depending on the size of the file, there can
be one to very many sectors allocated.
When this
file is deleted, all that happens is that
the space on the hard drive occupied by the
file is changed from "In Use" to
"Available". When another file is then
saved, all of this space may or may not be
used to store the new file. So, unless all
the space that the original file used is
overwritten with a new file, it will remain
on the hard drive.
Re-formatting the hard drive likewise, does
not completely remove the data that is
stored on it. It probably relocates the
tracks and sectors, but the zeros and ones
that made up the original file remain in
readable condition if the correct software
is used to retrieve it. The only way to
assure that all information on the hard
drive has been removed is to write over
every byte with non-descript data. The
primary standard for this is called the DoD
5220.22-M and is defined as:
US
Department of Defense in the clearing and
sanitizing standard DoD 5220.22-M recommends
the approach "Overwrite all addressable
locations with a character, its complement,
then a random character and verify" for
clearing and sanitizing information on a
writable media.
To do
this writing, a special program is needed.
One of the best and highly recommended is
also free. It is called "Darik's Boot &
Nuke" or "dban" for short. It can be
downloaded from
http://www.dban.org/ in two formats. One
in an .iso file that can be used to create a
bootable CD or DVD and the other an .exe
file that can be used to create a bootable
floppy or USB flash drive. This program by
default, uses the short
DoD 5220.22-M
method, but is also capable of using the "RCMP
TSSIT OPS-11", "Gutman", "PRNG Stream" and
"Quick Erase" methods. I won't go into these
other methods except to say that they
generate the data used to overwrite in
different ways.
In order
to assure that every byte on the hard drive
is overwritten, the hard drive cannot be in
use so the computer must be booted from a
CD, floppy or removable USB flash drive.
Of course, the computer's BIOS setup has to
be set to allow booting from the CD, floppy
or Flash drive.
Depending
on the method selected, this process of
overwriting every byte of a hard drive can
take many hours, so plan on plenty of time
to complete the wiping process. There is
another benefit from this wiping process.
Since every location is written, then read,
this process it serves as a very good,
rather intensive test of the hard drive
itself. |
