<s>
dvdisaster	B-Language
is	O
a	O
computer	B-Application
program	I-Application
aimed	O
to	O
enhance	O
data	O
survivability	O
on	O
optical	B-Device
discs	I-Device
by	O
creating	O
error	B-Error_Name
detection	I-Error_Name
and	I-Error_Name
correction	I-Error_Name
data	O
,	O
which	O
is	O
used	O
for	O
data	B-Application
recovery	I-Application
.	O
</s>
<s>
dvdisaster	B-Language
works	O
exclusively	O
at	O
the	O
image	O
level	O
.	O
</s>
<s>
This	O
program	O
can	O
be	O
used	O
either	O
to	O
generate	O
Error-Correcting	B-Error_Name
Code	O
(	O
ECC	O
)	O
data	O
from	O
an	O
existing	O
media	O
or	O
to	O
augment	O
an	O
ISO	B-General_Concept
image	I-General_Concept
with	O
ECC	O
data	O
prior	O
to	O
being	O
written	O
onto	O
a	O
medium	O
.	O
</s>
<s>
dvdisaster	B-Language
is	O
free	B-Application
software	I-Application
available	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
When	O
an	O
optical	B-Device
disc	I-Device
is	O
physically	O
damaged	O
(	O
such	O
as	O
by	O
scratching	O
)	O
,	O
or	O
has	O
begun	O
to	O
deteriorate	O
,	O
some	O
parts	O
of	O
the	O
data	O
on	O
the	O
disc	O
may	O
become	O
unreadable	O
.	O
</s>
<s>
By	O
utilizing	O
the	O
ECC	O
data	O
previously	O
generated	O
by	O
dvdisaster	B-Language
,	O
damaged	O
parts	O
of	O
the	O
disc	O
data	O
can	O
be	O
recovered	O
.	O
</s>
<s>
The	O
two	O
modes	O
of	O
ECC	O
data	O
generation	O
in	O
dvdisaster	B-Language
make	O
use	O
of	O
Reed	B-Error_Name
–	I-Error_Name
Solomon	I-Error_Name
codes	I-Error_Name
.	O
</s>
<s>
Alternatively	O
,	O
in	O
RS02	O
mode	O
,	O
the	O
ECC	O
data	O
is	O
appended	O
to	O
the	O
end	O
of	O
the	O
disc	O
image	O
before	O
the	O
image	O
is	O
burned	B-Application
to	O
disc	O
.	O
</s>
<s>
When	O
a	O
CD	O
or	O
DVD	O
has	O
been	O
augmented	O
in	O
RS02	O
mode	O
,	O
the	O
'	O
augmented	O
 '	O
section	O
of	O
the	O
data	O
remains	O
invisible	O
to	O
the	O
normal	O
user	O
,	O
and	O
the	O
disc	O
remains	O
fully	O
compatible	O
with	O
computers	O
without	O
knowledge	O
of	O
or	O
installation	O
of	O
dvdisaster	B-Language
.	O
</s>
<s>
In	O
this	O
way	O
a	O
damaged	O
disc	O
may	O
be	O
fully	O
recoverable	O
by	O
installing	O
the	O
software	O
,	O
accessing	O
the	O
Reed-Solomon	B-Error_Name
error	O
correcting	O
code	O
using	O
dvdisaster	B-Language
and	O
rebuilding	O
the	O
image	O
(	O
to	O
hard	O
disk	O
)	O
.	O
</s>
<s>
dvdisaster	B-Language
can	O
be	O
helpful	O
to	O
recover	O
the	O
contents	O
of	O
a	O
damaged	O
disc	O
even	O
when	O
no	O
ECC	O
data	O
is	O
available	O
.	O
</s>
<s>
dvdisaster	B-Language
can	O
then	O
repeatedly	O
rescan	O
just	O
the	O
missing	O
parts	O
until	O
all	O
damaged	O
areas	O
have	O
been	O
filled	O
in	O
by	O
correct	O
data	O
.	O
</s>
<s>
dvdisaster	B-Language
applies	O
an	O
image-based	O
approach	O
to	O
data	B-Application
recovery	I-Application
.	O
</s>
<s>
It	O
does	O
not	O
apply	O
a	O
file-based	O
data	B-Application
recovery	I-Application
,	O
as	O
reading	O
a	O
defective	O
medium	O
at	O
the	O
file	O
level	O
means	O
trying	O
to	O
read	O
as	O
much	O
data	O
as	O
possible	O
from	O
each	O
file	O
.	O
</s>
<s>
It	O
is	O
important	O
to	O
point	O
out	O
that	O
each	O
unit	O
of	O
ECC	O
data	O
dvdisaster	B-Language
places	O
at	O
the	O
end	O
is	O
calculated	O
from	O
sectors	O
of	O
the	O
original	O
data	O
spread	O
around	O
in	O
the	O
original	O
image	O
.	O
</s>
<s>
Clusters	O
are	O
different	O
in	O
Parchive	B-General_Concept
,	O
since	O
each	O
file	O
is	O
considered	O
as	O
a	O
single	O
block	O
:	O
with	O
dvdisaster	B-Language
data	O
loss	O
begins	O
when	O
one	O
of	O
the	O
clusters	O
has	O
more	O
than	O
about	O
15%	O
of	O
errors	O
(	O
unlikely	O
to	O
happen	O
but	O
theoretically	O
possible	O
with	O
few	O
KiB	O
of	O
data	O
)	O
,	O
while	O
Parchive	B-General_Concept
can	O
recover	O
any	O
error	O
,	O
provided	O
that	O
the	O
PAR2	O
files	O
are	O
intact	O
and	O
that	O
the	O
number	O
of	O
corrupted	O
files	O
(	O
it	O
does	O
n't	O
matter	O
how	O
much	O
corrupted	O
)	O
is	O
smaller	O
than	O
the	O
number	O
of	O
available	O
ECC	O
files	O
.	O
</s>
<s>
dvdisaster	B-Language
also	O
has	O
a	O
mode	O
with	O
separate	O
ECC	O
files	O
.	O
</s>
