<s>
In	O
computing	O
,	O
data	B-Application
recovery	I-Application
is	O
a	O
process	O
of	O
retrieving	O
deleted	O
,	O
inaccessible	O
,	O
lost	O
,	O
corrupted	O
,	O
damaged	O
,	O
or	O
formatted	O
data	O
from	O
secondary	O
storage	O
,	O
removable	B-Device
media	I-Device
or	O
files	B-Operating_System
,	O
when	O
the	O
data	O
stored	O
in	O
them	O
cannot	O
be	O
accessed	O
in	O
a	O
usual	O
way	O
.	O
</s>
<s>
The	O
data	O
is	O
most	O
often	O
salvaged	O
from	O
storage	O
media	O
such	O
as	O
internal	O
or	O
external	O
hard	B-Device
disk	I-Device
drives	I-Device
(	O
HDDs	O
)	O
,	O
solid-state	B-Device
drives	I-Device
(	O
SSDs	B-Device
)	O
,	O
USB	O
flash	O
drives	O
,	O
magnetic	B-Architecture
tapes	I-Architecture
,	O
CDs	B-Device
,	O
DVDs	O
,	O
RAID	B-Architecture
subsystems	O
,	O
and	O
other	O
electronic	O
devices	O
.	O
</s>
<s>
Recovery	O
may	O
be	O
required	O
due	O
to	O
physical	O
damage	O
to	O
the	O
storage	O
devices	O
or	O
logical	O
damage	O
to	O
the	O
file	B-Application
system	I-Application
that	O
prevents	O
it	O
from	O
being	O
mounted	B-Application
by	O
the	O
host	O
operating	B-General_Concept
system	I-General_Concept
(	O
OS	O
)	O
.	O
</s>
<s>
Logical	O
failures	O
occur	O
when	O
the	O
hard	B-Device
drive	I-Device
devices	O
are	O
functional	O
but	O
the	O
user	O
or	O
automated-OS	O
cannot	O
retrieve	O
or	O
access	O
date	O
stored	O
in	O
it	O
.	O
</s>
<s>
It	O
can	O
occur	O
due	O
to	O
corrupt	O
engineering	O
chip	O
,	O
lost	O
partitions	B-Application
,	O
deleted	O
data	O
,	O
firmware	B-Application
failure	O
,	O
failed	O
formatting/re	O
-installation	O
.	O
</s>
<s>
Data	B-Application
recovery	I-Application
can	O
be	O
a	O
very	O
simple	O
or	O
technical	O
challenge	O
.	O
</s>
<s>
The	O
most	O
common	O
data	B-Application
recovery	I-Application
scenarios	O
involve	O
an	O
operating	B-General_Concept
system	I-General_Concept
failure	O
,	O
malfunction	O
of	O
a	O
storage	O
device	O
,	O
logical	O
failure	O
of	O
storage	O
devices	O
,	O
accidental	O
damage	O
or	O
deletion	O
,	O
etc	O
.	O
</s>
<s>
(	O
typically	O
,	O
on	O
a	O
single-drive	O
,	O
single-partition	O
,	O
single-OS	O
system	O
)	O
,	O
in	O
which	O
case	O
the	O
ultimate	O
goal	O
is	O
simply	O
to	O
copy	O
all	O
important	O
files	B-Operating_System
from	O
the	O
damaged	O
media	O
to	O
another	O
new	O
drive	O
.	O
</s>
<s>
This	O
can	O
be	O
accomplished	O
using	O
a	O
Live	O
CD	B-Device
,	O
or	O
DVD	O
by	O
booting	O
directly	O
from	O
a	O
ROM	B-Device
or	O
a	O
USB	O
drive	O
instead	O
of	O
the	O
corrupted	O
drive	O
in	O
question	O
.	O
</s>
<s>
Many	O
Live	O
CDs	B-Device
or	O
DVDs	O
provide	O
a	O
means	O
to	O
mount	O
the	O
system	O
drive	O
and	O
backup	B-Protocol
drives	O
or	O
removable	B-Device
media	I-Device
,	O
and	O
to	O
move	O
the	O
files	B-Operating_System
from	O
the	O
system	O
drive	O
to	O
the	O
backup	B-Protocol
media	O
with	O
a	O
file	B-Application
manager	I-Application
or	O
optical	B-Device
disc	I-Device
authoring	O
software	O
.	O
</s>
<s>
Such	O
cases	O
can	O
often	O
be	O
mitigated	O
by	O
disk	B-Application
partitioning	I-Application
and	O
consistently	O
storing	O
valuable	O
data	O
files	B-Operating_System
(	O
or	O
copies	O
of	O
them	O
)	O
on	O
a	O
different	O
partition	B-Application
from	O
the	O
replaceable	O
OS	O
system	O
files	B-Operating_System
.	O
</s>
<s>
Another	O
scenario	O
involves	O
a	O
drive-level	O
failure	O
,	O
such	O
as	O
a	O
compromised	O
file	B-Application
system	I-Application
or	O
drive	B-Application
partition	I-Application
,	O
or	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
failure	I-Device
.	O
</s>
<s>
Depending	O
on	O
the	O
situation	O
,	O
solutions	O
involve	O
repairing	O
the	O
logical	O
file	B-Application
system	I-Application
,	O
partition	B-Application
table	O
,	O
or	O
master	B-Device
boot	I-Device
record	I-Device
,	O
or	O
updating	O
the	O
firmware	B-Application
or	O
drive	O
recovery	O
techniques	O
ranging	O
from	O
software-based	O
recovery	O
of	O
corrupted	O
data	O
,	O
to	O
hardware	O
-	O
and	O
software-based	O
recovery	O
of	O
damaged	O
service	O
areas	O
(	O
also	O
known	O
as	O
the	O
hard	B-Device
disk	I-Device
drive	I-Device
's	O
"	O
firmware	B-Application
"	O
)	O
,	O
to	O
hardware	O
replacement	O
on	O
a	O
physically	O
damaged	O
drive	O
which	O
allows	O
for	O
the	O
extraction	O
of	O
data	O
to	O
a	O
new	O
drive	O
.	O
</s>
<s>
In	O
a	O
third	O
scenario	O
,	O
files	B-Operating_System
have	O
been	O
accidentally	O
"	O
deleted	O
"	O
from	O
a	O
storage	O
medium	O
by	O
the	O
users	O
.	O
</s>
<s>
Typically	O
,	O
the	O
contents	O
of	O
deleted	O
files	B-Operating_System
are	O
not	O
removed	O
immediately	O
from	O
the	O
physical	O
drive	O
;	O
instead	O
,	O
references	O
to	O
them	O
in	O
the	O
directory	O
structure	O
are	O
removed	O
,	O
and	O
thereafter	O
space	O
the	O
deleted	O
data	O
occupy	O
is	O
made	O
available	O
for	O
later	O
data	O
overwriting	O
.	O
</s>
<s>
In	O
the	O
mind	O
of	O
end	O
users	O
,	O
deleted	O
files	B-Operating_System
cannot	O
be	O
discoverable	O
through	O
a	O
standard	O
file	B-Application
manager	I-Application
,	O
but	O
the	O
deleted	O
data	O
still	O
technically	O
exists	O
on	O
the	O
physical	O
drive	O
.	O
</s>
<s>
In	O
the	O
meantime	O
,	O
the	O
original	O
file	O
contents	O
remain	O
,	O
often	O
several	O
disconnected	O
fragments	B-Application
,	O
and	O
may	O
be	O
recoverable	O
if	O
not	O
overwritten	O
by	O
other	O
data	O
files	B-Operating_System
.	O
</s>
<s>
The	O
term	O
"	O
data	B-Application
recovery	I-Application
"	O
is	O
also	O
used	O
in	O
the	O
context	O
of	O
forensic	O
applications	O
or	O
espionage	O
,	O
where	O
data	O
which	O
have	O
been	O
encrypted	O
,	O
hidden	O
,	O
or	O
deleted	O
,	O
rather	O
than	O
damaged	O
,	O
are	O
recovered	O
.	O
</s>
<s>
CD-ROMs	B-Device
can	O
have	O
their	O
metallic	O
substrate	O
or	O
dye	O
layer	O
scratched	O
off	O
;	O
hard	B-Device
disks	I-Device
can	O
suffer	O
from	O
a	O
multitude	O
of	O
mechanical	O
failures	O
,	O
such	O
as	O
head	O
crashes	O
,	O
PCB	O
failure	O
,	O
and	O
failed	O
motors	O
;	O
tapes	O
can	O
simply	O
break	O
.	O
</s>
<s>
Physical	O
damage	O
to	O
a	O
hard	B-Device
drive	I-Device
,	O
even	O
in	O
cases	O
where	O
a	O
head	O
crash	O
has	O
occurred	O
,	O
does	O
not	O
necessarily	O
mean	O
there	O
will	O
be	O
a	O
permanent	O
loss	O
of	O
data	O
.	O
</s>
<s>
The	O
techniques	O
employed	O
by	O
many	O
professional	O
data	B-Application
recovery	I-Application
companies	O
can	O
typically	O
salvage	O
most	O
,	O
if	O
not	O
all	O
,	O
of	O
the	O
data	O
that	O
had	O
been	O
lost	O
when	O
the	O
failure	O
occurred	O
.	O
</s>
<s>
Of	O
course	O
,	O
there	O
are	O
exceptions	O
to	O
this	O
,	O
such	O
as	O
cases	O
where	O
severe	O
damage	O
to	O
the	O
hard	B-Device
drive	I-Device
platters	I-Device
may	O
have	O
occurred	O
.	O
</s>
<s>
However	O
,	O
if	O
the	O
hard	B-Device
drive	I-Device
can	O
be	O
repaired	O
and	O
a	O
full	O
image	O
or	O
clone	O
created	O
,	O
then	O
the	O
logical	O
file	O
structure	O
can	O
be	O
rebuilt	O
in	O
most	O
instances	O
.	O
</s>
<s>
For	O
example	O
,	O
opening	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
in	O
a	O
normal	O
environment	O
can	O
allow	O
airborne	O
dust	O
to	O
settle	O
on	O
the	O
platter	O
and	O
become	O
caught	O
between	O
the	O
platter	O
and	O
the	O
read/write	B-Device
head	I-Device
.	O
</s>
<s>
During	O
normal	O
operation	O
,	O
read/write	B-Device
heads	I-Device
float	O
3	O
to	O
6	O
nanometers	O
above	O
the	O
platter	O
surface	O
,	O
and	O
the	O
average	O
dust	O
particles	O
found	O
in	O
a	O
normal	O
environment	O
are	O
typically	O
around	O
30,000	O
nanometers	O
in	O
diameter	O
.	O
</s>
<s>
When	O
these	O
dust	O
particles	O
get	O
caught	O
between	O
the	O
read/write	B-Device
heads	I-Device
and	O
the	O
platter	O
,	O
they	O
can	O
cause	O
new	O
head	O
crashes	O
that	O
further	O
damage	O
the	O
platter	O
and	O
thus	O
compromise	O
the	O
recovery	O
process	O
.	O
</s>
<s>
Consequently	O
,	O
data	B-Application
recovery	I-Application
companies	O
are	O
often	O
employed	O
to	O
salvage	O
important	O
data	O
with	O
the	O
more	O
reputable	O
ones	O
using	O
class	O
100	O
dust	O
-	O
and	O
static-free	O
cleanrooms	B-Application
.	O
</s>
<s>
Some	O
damage	O
can	O
be	O
repaired	O
by	O
replacing	O
parts	O
in	O
the	O
hard	B-Device
disk	I-Device
.	O
</s>
<s>
Once	O
this	O
image	O
is	O
acquired	O
and	O
saved	O
on	O
a	O
reliable	O
medium	O
,	O
the	O
image	O
can	O
be	O
safely	O
analyzed	O
for	O
logical	O
damage	O
and	O
will	O
possibly	O
allow	O
much	O
of	O
the	O
original	O
file	B-Application
system	I-Application
to	O
be	O
reconstructed	O
.	O
</s>
<s>
While	O
this	O
may	O
work	O
in	O
rare	O
circumstances	O
on	O
hard	B-Device
disk	I-Device
drives	I-Device
manufactured	O
before	O
2003	O
,	O
it	O
will	O
not	O
work	O
on	O
newer	O
drives	O
.	O
</s>
<s>
Some	O
manufacturers	O
(	O
Seagate	O
,	O
for	O
example	O
)	O
store	O
this	O
information	O
on	O
a	O
serial	O
EEPROM	B-General_Concept
chip	O
,	O
which	O
can	O
be	O
removed	O
and	O
transferred	O
to	O
the	O
replacement	O
board	O
.	O
</s>
<s>
Each	O
hard	B-Device
disk	I-Device
drive	I-Device
has	O
what	O
is	O
called	O
a	O
system	O
area	O
or	O
service	O
area	O
;	O
this	O
portion	O
of	O
the	O
drive	O
,	O
which	O
is	O
not	O
directly	O
accessible	O
to	O
the	O
end	O
user	O
,	O
usually	O
contains	O
drive	O
's	O
firmware	B-Application
and	O
adaptive	O
data	O
that	O
helps	O
the	O
drive	O
operate	O
within	O
normal	O
parameters	O
.	O
</s>
<s>
The	O
sector	O
lists	O
are	O
also	O
stored	O
on	O
various	O
chips	O
attached	O
to	O
the	O
PCB	O
,	O
and	O
they	O
are	O
unique	O
to	O
each	O
hard	B-Device
disk	I-Device
drive	I-Device
.	O
</s>
<s>
In	O
most	O
cases	O
the	O
drive	B-Device
heads	I-Device
will	O
click	O
because	O
they	O
are	O
unable	O
to	O
find	O
the	O
data	O
matching	O
what	O
is	O
stored	O
on	O
the	O
PCB	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
data	O
on	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
can	O
be	O
unreadable	O
due	O
to	O
damage	O
to	O
the	O
partition	B-Application
table	O
or	O
file	B-Application
system	I-Application
,	O
or	O
to	O
(	O
intermittent	O
)	O
media	O
errors	O
.	O
</s>
<s>
In	O
the	O
majority	O
of	O
these	O
cases	O
,	O
at	O
least	O
a	O
portion	O
of	O
the	O
original	O
data	O
can	O
be	O
recovered	O
by	O
repairing	O
the	O
damaged	O
partition	B-Application
table	O
or	O
file	B-Application
system	I-Application
using	O
specialized	O
data	B-Application
recovery	I-Application
software	I-Application
such	O
as	O
Testdisk	B-Application
;	O
software	O
like	O
ddrescue	B-Language
can	O
image	O
media	O
despite	O
intermittent	O
errors	O
,	O
and	O
image	O
raw	O
data	O
when	O
there	O
is	O
partition	B-Application
table	O
or	O
file	B-Application
system	I-Application
damage	O
.	O
</s>
<s>
This	O
type	O
of	O
data	B-Application
recovery	I-Application
can	O
be	O
performed	O
by	O
people	O
without	O
expertise	O
in	O
drive	O
hardware	O
as	O
it	O
requires	O
no	O
special	O
physical	O
equipment	O
or	O
access	O
to	O
platters	B-Device
.	O
</s>
<s>
Sometimes	O
data	O
can	O
be	O
recovered	O
using	O
relatively	O
simple	O
methods	O
and	O
tools	O
;	O
more	O
serious	O
cases	O
can	O
require	O
expert	O
intervention	O
,	O
particularly	O
if	O
parts	O
of	O
files	B-Operating_System
are	O
irrecoverable	O
.	O
</s>
<s>
Data	O
carving	O
is	O
the	O
recovery	O
of	O
parts	O
of	O
damaged	O
files	B-Operating_System
using	O
knowledge	O
of	O
their	O
structure	O
.	O
</s>
<s>
After	O
data	O
has	O
been	O
physically	O
overwritten	O
on	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
,	O
it	O
is	O
generally	O
assumed	O
that	O
the	O
previous	O
data	O
are	O
no	O
longer	O
possible	O
to	O
recover	O
.	O
</s>
<s>
To	O
guard	O
against	O
this	O
type	O
of	O
data	B-Application
recovery	I-Application
,	O
Gutmann	O
and	O
Colin	O
Plumb	O
designed	O
a	O
method	O
of	O
irreversibly	O
scrubbing	O
data	O
,	O
known	O
as	O
the	O
Gutmann	B-Algorithm
method	I-Algorithm
and	O
used	O
by	O
several	O
disk-scrubbing	O
software	O
packages	O
.	O
</s>
<s>
Solid-state	B-Device
drives	I-Device
(	O
SSD	B-Device
)	O
overwrite	O
data	O
differently	O
from	O
hard	B-Device
disk	I-Device
drives	I-Device
(	O
HDD	O
)	O
which	O
makes	O
at	O
least	O
some	O
of	O
their	O
data	O
easier	O
to	O
recover	O
.	O
</s>
<s>
Most	O
SSDs	B-Device
use	O
flash	B-Device
memory	I-Device
to	O
store	O
data	O
in	O
pages	O
and	O
blocks	O
,	O
referenced	O
by	O
logical	B-Device
block	I-Device
addresses	I-Device
(	O
LBA	O
)	O
which	O
are	O
managed	O
by	O
the	O
flash	O
translation	O
layer	O
(	O
FTL	O
)	O
.	O
</s>
<s>
This	O
leaves	O
the	O
pre-modification	O
data	O
in	O
place	O
,	O
with	O
possibly	O
many	O
generations	O
,	O
and	O
recoverable	O
by	O
data	B-Application
recovery	I-Application
software	I-Application
.	O
</s>
<s>
Sometimes	O
,	O
data	O
present	O
in	O
the	O
physical	O
drives	O
(	O
Internal/External	O
Hard	B-Device
disk	I-Device
,	O
Pen	O
Drive	O
,	O
etc	O
.	O
)	O
</s>
<s>
In	O
these	O
cases	O
,	O
data	B-Application
recovery	I-Application
software	I-Application
is	O
used	O
to	O
recover/restore	O
the	O
data	O
files	B-Operating_System
.	O
</s>
<s>
In	O
the	O
list	O
of	O
logical	O
failures	O
of	O
hard	B-Device
disks	I-Device
,	O
a	O
logical	O
bad	O
sector	O
is	O
the	O
most	O
common	O
fault	O
leading	O
data	O
not	O
to	O
be	O
readable	O
.	O
</s>
<s>
Sometimes	O
it	O
is	O
possible	O
to	O
sidestep	O
error	B-Error_Name
detection	I-Error_Name
even	O
in	O
software	O
,	O
and	O
perhaps	O
with	O
repeated	O
reading	O
and	O
statistical	O
analysis	O
recover	O
at	O
least	O
some	O
of	O
the	O
underlying	O
stored	O
data	O
.	O
</s>
<s>
Sometimes	O
prior	O
knowledge	O
of	O
the	O
data	O
stored	O
and	O
the	O
error	B-Error_Name
detection	I-Error_Name
and	I-Error_Name
correction	I-Error_Name
codes	O
can	O
be	O
used	O
to	O
recover	O
even	O
erroneous	O
data	O
.	O
</s>
<s>
Usually	O
,	O
there	O
are	O
four	O
phases	O
when	O
it	O
comes	O
to	O
successful	O
data	B-Application
recovery	I-Application
,	O
though	O
that	O
can	O
vary	O
depending	O
on	O
the	O
type	O
of	O
data	O
corruption	O
and	O
recovery	O
required	O
.	O
</s>
<s>
The	O
hard	B-Device
drive	I-Device
is	O
repaired	O
in	O
order	O
to	O
get	O
it	O
running	O
in	O
some	O
form	O
,	O
or	O
at	O
least	O
in	O
a	O
state	O
suitable	O
for	O
reading	O
the	O
data	O
from	O
it	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
heads	O
are	O
bad	O
they	O
need	O
to	O
be	O
changed	O
;	O
if	O
the	O
PCB	O
is	O
faulty	O
then	O
it	O
needs	O
to	O
be	O
fixed	O
or	O
replaced	O
;	O
if	O
the	O
spindle	O
motor	O
is	O
bad	O
the	O
platters	B-Device
and	O
heads	O
should	O
be	O
moved	O
to	O
a	O
new	O
drive	O
.	O
</s>
<s>
When	O
a	O
hard	B-Device
disk	I-Device
drive	I-Device
fails	O
,	O
the	O
importance	O
of	O
getting	O
the	O
data	O
off	O
the	O
drive	O
is	O
the	O
top	O
priority	O
.	O
</s>
<s>
The	O
longer	O
a	O
faulty	O
drive	O
is	O
used	O
,	O
the	O
more	O
likely	O
further	O
data	B-General_Concept
loss	I-General_Concept
is	O
to	O
occur	O
.	O
</s>
<s>
Using	O
the	O
clone	O
it	O
may	O
be	O
possible	O
to	O
repair	O
the	O
partition	B-Application
table	O
or	O
master	B-Device
boot	I-Device
record	I-Device
(	O
MBR	O
)	O
in	O
order	O
to	O
read	O
the	O
file	B-Application
system	I-Application
's	O
data	O
structure	O
and	O
retrieve	O
stored	O
data	O
.	O
</s>
<s>
The	O
Windows	B-Application
operating	I-Application
system	I-Application
can	O
be	O
reinstalled	O
on	O
a	O
computer	O
that	O
is	O
already	O
licensed	O
for	O
it	O
.	O
</s>
<s>
The	O
reinstallation	O
can	O
be	O
done	O
by	O
downloading	O
the	O
operating	B-General_Concept
system	I-General_Concept
or	O
by	O
using	O
a	O
"	O
restore	O
disk	O
"	O
provided	O
by	O
the	O
computer	O
manufacturer	O
.	O
</s>
<s>
Data	B-Application
recovery	I-Application
cannot	O
always	O
be	O
done	O
on	O
a	O
running	O
system	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
a	O
boot	B-Operating_System
disk	I-Operating_System
,	O
live	O
CD	B-Device
,	O
live	O
USB	O
,	O
or	O
any	O
other	O
type	O
of	O
live	O
distro	O
contains	O
a	O
minimal	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
BartPE	B-Application
:	O
a	O
lightweight	O
variant	O
of	O
Microsoft	B-Application
Windows	I-Application
XP	I-Application
or	O
Windows	B-Application
Server	I-Application
2003	I-Application
32-bit	O
operating	B-General_Concept
systems	I-General_Concept
,	O
similar	O
to	O
a	O
Windows	B-Application
Preinstallation	O
Environment	O
,	O
which	O
can	O
be	O
run	O
from	O
a	O
live	O
CD	B-Device
or	O
live	O
USB	O
drive	O
.	O
</s>
<s>
Windows	B-Application
Preinstallation	O
Environment	O
(	O
WinPE	O
)	O
:	O
A	O
customizable	O
Windows	B-Application
Boot	O
DVD	O
(	O
made	O
by	O
Microsoft	O
and	O
distributed	O
for	O
free	O
)	O
.	O
</s>
<s>
from	O
Nero	O
AG	O
:	O
"	O
Data	O
Reliability	O
"	O
feature	O
generates	O
redundant	O
and	O
checksum	O
data	O
in	O
the	O
remaining	O
space	O
of	O
optical	B-Device
discs	I-Device
.	O
</s>
<s>
TestDisk	B-Application
:	O
free	O
,	O
open	O
source	O
,	O
multi-platform	O
.	O
</s>
<s>
The	B-Application
Sleuth	I-Application
Kit	I-Application
:	O
also	O
known	O
as	O
TSK	O
,	O
a	O
suite	O
of	O
forensic	O
analysis	O
tools	O
developed	O
by	O
Brian	O
Carrier	O
for	O
UNIX	O
,	O
Linux	O
and	O
Windows	B-Application
systems	O
.	O
</s>
