<s>
An	O
optical	B-Device
disc	I-Device
is	O
a	O
flat	O
,	O
usually	O
disc-shaped	O
object	O
that	O
stores	O
information	O
in	O
the	O
form	O
of	O
physical	O
variations	O
on	O
its	O
surface	O
that	O
can	O
be	O
read	O
with	O
the	O
aid	O
of	O
a	O
beam	O
of	O
light	O
.	O
</s>
<s>
Optical	B-Device
discs	I-Device
can	O
be	O
reflective	O
,	O
where	O
the	O
light	O
source	O
and	O
detector	O
are	O
on	O
the	O
same	O
side	O
of	O
the	O
disc	O
,	O
or	O
transmissive	O
,	O
where	O
light	O
shines	O
through	O
the	O
disc	O
to	O
the	O
be	O
detected	O
on	O
the	O
other	O
side	O
.	O
</s>
<s>
Optical	B-Device
discs	I-Device
can	O
store	O
analog	O
information	O
(	O
e.g.	O
</s>
<s>
CD	B-Device
Video	I-Device
)	O
.	O
</s>
<s>
The	O
encoding	O
material	O
sits	O
atop	O
a	O
thicker	O
substrate	B-Architecture
(	O
usually	O
polycarbonate	O
)	O
that	O
makes	O
up	O
the	O
bulk	O
of	O
the	O
disc	O
and	O
forms	O
a	O
dust	O
defocusing	O
layer	O
.	O
</s>
<s>
The	O
data	O
are	O
stored	O
on	O
the	O
disc	O
with	O
a	O
laser	O
or	O
stamping	B-Device
machine	I-Device
,	O
and	O
can	O
be	O
accessed	O
when	O
the	O
data	O
path	O
is	O
illuminated	O
with	O
a	O
laser	O
diode	O
in	O
an	O
optical	B-Device
disc	I-Device
drive	O
that	O
spins	O
the	O
disc	O
at	O
speeds	O
of	O
about	O
200	O
to	O
4,000	O
RPM	O
or	O
more	O
,	O
depending	O
on	O
the	O
drive	O
type	O
,	O
disc	O
format	O
,	O
and	O
the	O
distance	O
of	O
the	O
read	O
head	O
from	O
the	O
center	O
of	O
the	O
disc	O
(	O
outer	O
tracks	O
are	O
read	O
at	O
a	O
higher	O
data	O
speed	O
due	O
to	O
higher	O
linear	B-Device
velocities	I-Device
at	O
the	O
same	O
angular	B-Device
velocities	I-Device
)	O
.	O
</s>
<s>
Most	O
optical	B-Device
discs	I-Device
exhibit	O
a	O
characteristic	O
iridescence	O
as	O
a	O
result	O
of	O
the	O
diffraction	O
grating	O
formed	O
by	O
their	O
grooves	O
.	O
</s>
<s>
The	O
reverse	O
side	O
of	O
an	O
optical	B-Device
disc	I-Device
usually	O
has	O
a	O
printed	O
label	O
,	O
sometimes	O
made	O
of	O
paper	O
but	O
often	O
printed	O
or	O
stamped	O
onto	O
the	O
disc	O
itself	O
.	O
</s>
<s>
Unlike	O
the	O
3-inch	O
floppy	B-Device
disk	I-Device
,	O
most	O
optical	B-Device
discs	I-Device
do	O
not	O
have	O
an	O
integrated	O
protective	O
casing	O
and	O
are	O
therefore	O
susceptible	O
to	O
data	O
transfer	O
problems	O
due	O
to	O
scratches	O
,	O
fingerprints	O
,	O
and	O
other	O
environmental	O
problems	O
.	O
</s>
<s>
Optical	B-Device
discs	I-Device
are	O
usually	O
between	O
in	O
diameter	O
,	O
with	O
being	O
the	O
most	O
common	O
size	O
.	O
</s>
<s>
An	O
optical	B-Device
disc	I-Device
is	O
designed	O
to	O
support	O
one	O
of	O
three	O
recording	O
types	O
:	O
read-only	O
(	O
e.g.	O
</s>
<s>
:	O
CD	O
and	O
CD-ROM	B-Device
)	O
,	O
recordable	O
(	O
write-once	O
,	O
e.g.	O
</s>
<s>
Write-once	O
optical	B-Device
discs	I-Device
commonly	O
have	O
an	O
organic	O
dye	O
(	O
may	O
also	O
be	O
a	O
(	O
Phthalocyanine	O
)	O
Azo	O
dye	O
,	O
mainly	O
used	O
by	O
Verbatim	O
,	O
or	O
an	O
oxonol	O
dye	O
,	O
used	O
by	O
Fujifilm	O
)	O
recording	O
layer	O
between	O
the	O
substrate	B-Architecture
and	O
the	O
reflective	O
layer	O
.	O
</s>
<s>
Rewritable	O
discs	O
typically	O
contain	O
an	O
alloy	B-Application
recording	O
layer	O
composed	O
of	O
a	O
phase	O
change	O
material	O
,	O
most	O
often	O
AgInSbTe	O
,	O
an	O
alloy	B-Application
of	O
silver	O
,	O
indium	O
,	O
antimony	O
,	O
and	O
tellurium	O
.	O
</s>
<s>
The	O
type	O
of	O
dye	O
and	O
the	O
material	O
used	O
on	O
the	O
reflective	O
layer	O
on	O
an	O
optical	B-Device
disc	I-Device
may	O
be	O
determined	O
by	O
shining	O
a	O
light	O
through	O
the	O
disc	O
,	O
as	O
different	O
dye	O
and	O
material	O
combinations	O
have	O
different	O
colors	O
.	O
</s>
<s>
Blu-ray	B-Operating_System
Disc	I-Operating_System
recordable	I-Operating_System
discs	O
do	O
not	O
usually	O
use	O
an	O
organic	O
dye	O
recording	O
layer	O
,	O
instead	O
using	O
an	O
inorganic	O
recording	O
layer	O
.	O
</s>
<s>
Optical	B-Device
discs	I-Device
are	O
often	O
stored	O
in	O
special	O
cases	O
sometimes	O
called	O
jewel	O
cases	O
and	O
are	O
most	O
commonly	O
used	O
for	O
digital	O
preservation	O
,	O
storing	O
music	O
(	O
e.g.	O
</s>
<s>
for	O
use	O
in	O
a	O
Blu-ray	O
player	O
)	O
,	O
or	O
data	O
and	O
programs	O
for	O
personal	B-Device
computers	I-Device
(	O
PC	O
)	O
,	O
as	O
well	O
as	O
offline	O
hard	B-General_Concept
copy	I-General_Concept
data	O
distribution	O
due	O
to	O
lower	O
per-unit	O
prices	O
than	O
other	O
types	O
of	O
media	O
.	O
</s>
<s>
The	O
Optical	B-General_Concept
Storage	I-General_Concept
Technology	O
Association	O
(	O
OSTA	O
)	O
promoted	O
standardized	O
optical	B-General_Concept
storage	I-General_Concept
formats	O
.	O
</s>
<s>
Libraries	O
and	O
archives	O
enact	O
optical	B-Device
media	I-Device
preservation	O
procedures	O
to	O
ensure	O
continued	O
usability	O
in	O
the	O
computer	O
's	O
optical	B-Device
disc	I-Device
drive	O
or	O
corresponding	O
disc	O
player	O
.	O
</s>
<s>
File	O
operations	O
of	O
traditional	O
mass	B-Device
storage	I-Device
devices	I-Device
such	O
as	O
flash	B-Device
drives	I-Device
,	O
memory	B-Device
cards	I-Device
and	O
hard	B-Device
drives	I-Device
can	O
be	O
simulated	O
using	O
a	O
UDF	O
live	O
file	O
system	O
.	O
</s>
<s>
For	O
computer	O
data	O
backup	O
and	O
physical	O
data	O
transfer	O
,	O
optical	B-Device
discs	I-Device
such	O
as	O
CDs	O
and	O
DVDs	O
are	O
gradually	O
being	O
replaced	O
with	O
faster	O
,	O
smaller	O
solid-state	O
devices	O
,	O
especially	O
the	O
USB	O
flash	B-Device
drive	I-Device
.	O
</s>
<s>
This	O
trend	O
is	O
expected	O
to	O
continue	O
as	O
USB	O
flash	B-Device
drives	I-Device
continue	O
to	O
increase	O
in	O
capacity	O
and	O
drop	O
in	O
price	O
.	O
</s>
<s>
However	O
,	O
audio	O
CDs	O
and	O
Blu-rays	O
are	O
still	O
preferred	O
and	O
bought	O
by	O
some	O
,	O
as	O
a	O
way	O
of	O
supporting	O
their	O
favorite	O
works	O
while	O
getting	O
something	O
tangible	O
in	O
return	O
and	O
also	O
since	O
audio	O
CDs	O
(	O
alongside	O
vinyl	O
records	O
and	O
cassette	B-Device
tapes	I-Device
)	O
contain	O
uncompressed	B-General_Concept
audio	O
without	O
the	O
artifacts	O
introduced	O
by	O
lossy	B-Algorithm
compression	I-Algorithm
algorithms	O
like	O
MP3	B-Application
,	O
and	O
Blu-rays	O
offer	O
better	O
image	O
and	O
sound	O
quality	O
than	O
streaming	O
media	O
,	O
without	O
visible	O
compression	O
artifacts	O
,	O
due	O
to	O
higher	O
bitrates	O
and	O
more	O
available	O
storage	O
space	O
.	O
</s>
<s>
However	O
,	O
Blu-rays	O
may	O
sometimes	O
be	O
torrented	B-Protocol
over	O
the	O
internet	O
,	O
but	O
torrenting	B-Protocol
may	O
not	O
be	O
an	O
option	O
for	O
some	O
,	O
due	O
to	O
restrictions	O
put	O
in	O
place	O
by	O
ISPs	O
on	O
legal	O
or	O
copyright	O
grounds	O
,	O
low	O
download	O
speeds	O
or	O
not	O
having	O
enough	O
available	O
storage	O
space	O
,	O
since	O
the	O
content	O
may	O
weigh	O
up	O
to	O
several	O
dozen	O
gigabytes	O
.	O
</s>
<s>
Blu-rays	O
may	O
be	O
the	O
only	O
option	O
for	O
those	O
looking	O
to	O
play	O
large	O
games	O
without	O
having	O
to	O
download	O
them	O
over	O
an	O
unreliable	O
or	O
slow	O
internet	O
connection	O
,	O
which	O
is	O
the	O
reason	O
why	O
they	O
are	O
still	O
(	O
as	O
of	O
2020	O
)	O
widely	O
used	O
by	O
gaming	O
consoles	O
,	O
like	O
the	B-Operating_System
PlayStation	I-Operating_System
4	I-Operating_System
and	O
Xbox	O
One	O
X	O
.	O
</s>
<s>
The	O
ISO	O
Standard	O
18938:2008	O
is	O
about	O
best	O
optical	B-Device
disc	I-Device
handling	O
techniques	O
.	O
</s>
<s>
Optical	B-Device
disc	I-Device
cleaning	O
should	O
never	O
be	O
done	O
in	O
a	O
circular	O
pattern	O
,	O
to	O
avoid	O
concentric	O
cirles	O
from	O
forming	O
on	O
the	O
disc	O
.	O
</s>
<s>
Optical	B-Device
discs	I-Device
should	O
be	O
stored	O
in	O
dry	O
and	O
cool	O
conditions	O
to	O
increase	O
longevity	O
,	O
with	O
temperatures	O
between	O
-10	O
and	O
23°C	O
,	O
never	O
exceeding	O
32°C	O
,	O
and	O
with	O
humidity	O
never	O
falling	O
below	O
10%	O
,	O
with	O
recommended	O
storage	O
at	O
20	O
to	O
50%	O
of	O
humidity	O
without	O
fluctuations	O
of	O
more	O
than	O
±10%	O
.	O
</s>
<s>
Although	O
optical	B-Device
discs	I-Device
are	O
more	O
durable	O
than	O
earlier	O
audio-visual	O
and	O
data	B-General_Concept
storage	I-General_Concept
formats	O
,	O
they	O
are	O
susceptible	O
to	O
environmental	O
and	O
daily-use	O
damage	O
,	O
if	O
handled	O
improperly	O
.	O
</s>
<s>
Optical	B-Device
discs	I-Device
are	O
not	O
prone	O
to	O
uncontrollable	O
catastrophic	O
failures	O
such	O
as	O
head	O
crashes	O
,	O
power	O
surges	O
,	O
or	O
exposure	O
to	O
water	O
like	O
hard	B-Device
disk	I-Device
drives	I-Device
and	O
flash	B-Device
storage	I-Device
,	O
since	O
optical	O
drives	O
 '	O
storage	O
controllers	O
are	O
not	O
tied	O
to	O
optical	B-Device
discs	I-Device
themselves	O
like	O
with	O
hard	B-Device
disk	I-Device
drives	I-Device
and	O
flash	B-Device
memory	I-Device
controllers	I-Device
,	O
and	O
a	O
disc	O
is	O
usually	O
recoverable	O
from	O
a	O
defective	O
optical	O
drive	O
by	O
pushing	O
an	O
unsharp	O
needle	O
into	O
the	O
emergency	O
ejection	O
pinhole	O
,	O
and	O
has	O
no	O
point	O
of	O
immediate	O
water	O
ingress	O
and	O
no	O
integrated	O
circuitry	O
.	O
</s>
<s>
Malware	O
is	O
unable	O
to	O
spread	O
over	O
factory-pressed	O
media	O
,	O
finalized	O
media	O
,	O
or	O
-ROM	O
(	O
read-only	B-Device
memory	I-Device
)	O
drive	O
types	O
whose	O
lasers	O
lack	O
the	O
strength	O
to	O
write	O
data	O
.	O
</s>
<s>
Malware	O
is	O
conventionally	O
programmed	O
to	O
detect	O
and	O
spread	O
over	O
traditional	O
mass	B-Device
storage	I-Device
devices	I-Device
such	O
as	O
flash	B-Device
drives	I-Device
,	O
external	O
solid	B-Device
state	I-Device
drives	I-Device
and	O
hard	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
The	O
first	O
recorded	O
historical	O
use	O
of	O
an	O
optical	B-Device
disc	I-Device
was	O
in	O
1884	O
when	O
Alexander	O
Graham	O
Bell	O
,	O
Chichester	O
Bell	O
and	O
Charles	O
Sumner	O
Tainter	O
recorded	O
sound	O
on	O
a	O
glass	O
disc	O
using	O
a	O
beam	O
of	O
light	O
.	O
</s>
<s>
An	O
early	O
analogue	O
optical	B-Device
disc	I-Device
system	O
existed	O
in	O
1935	O
,	O
used	O
on	O
Welte	O
's	O
sampling	O
organ	O
.	O
</s>
<s>
An	O
early	O
analog	O
optical	B-Device
disc	I-Device
used	O
for	O
video	O
recording	O
was	O
invented	O
by	O
David	O
Paul	O
Gregg	O
in	O
1958	O
and	O
patented	O
in	O
the	O
US	O
in	O
1961	O
and	O
1969	O
.	O
</s>
<s>
This	O
form	O
of	O
optical	B-Device
disc	I-Device
was	O
a	O
very	O
early	O
form	O
of	O
the	O
DVD	O
(	O
)	O
.	O
</s>
<s>
Both	O
Gregg	O
's	O
and	O
Russell	O
's	O
disc	O
are	O
floppy	B-Device
media	O
read	O
in	O
transparent	O
mode	O
,	O
which	O
imposes	O
serious	O
drawbacks	O
.	O
</s>
<s>
Kramer	O
's	O
physical	O
format	O
is	O
used	O
in	O
all	O
optical	B-Device
discs	I-Device
.	O
</s>
<s>
In	O
1979	O
,	O
Exxon	O
STAR	O
Systems	O
in	O
Pasadena	O
,	O
CA	O
built	O
a	O
computer	O
controlled	O
WORM	B-Device
drive	I-Device
that	O
utilized	O
thin	O
film	O
coatings	O
of	O
Tellurium	O
and	O
Selenium	O
on	O
a	O
12	O
"	O
diameter	O
glass	O
disk	O
.	O
</s>
<s>
STAR	O
Systems	O
was	O
bought	O
by	O
Storage	O
Technology	O
Corporation	O
(	O
STC	O
)	O
in	O
1981	O
and	O
moved	O
to	O
Boulder	O
,	O
CO	O
.	O
Development	O
of	O
the	O
WORM	B-Device
technology	O
was	O
continued	O
using	O
14	O
"	O
diameter	O
aluminum	O
substrates	B-Architecture
.	O
</s>
<s>
The	O
CD-ROM	B-Device
format	O
was	O
developed	O
by	O
Sony	O
and	O
Philips	O
,	O
introduced	O
in	O
1984	O
,	O
as	O
an	O
extension	O
of	O
Compact	O
Disc	O
Digital	O
Audio	O
and	O
adapted	O
to	O
hold	O
any	O
form	O
of	O
digital	O
data	O
.	O
</s>
<s>
The	O
same	O
year	O
,	O
Sony	O
demonstrated	O
a	O
LaserDisc	O
data	B-General_Concept
storage	I-General_Concept
format	O
,	O
with	O
a	O
larger	O
data	O
capacity	O
of	O
3.28	O
GB	O
.	O
</s>
<s>
In	O
the	O
late	O
1980s	O
and	O
early	O
1990s	O
,	O
Optex	O
,	O
Inc	O
.	O
of	O
Rockville	O
,	O
MD	O
,	O
built	O
an	O
erasable	O
optical	O
digital	O
video	O
disc	O
system	O
using	O
Electron	O
Trapping	O
Optical	B-Device
Media	I-Device
(	O
ETOM	O
)	O
.	O
</s>
<s>
In	O
the	O
mid-1990s	O
,	O
a	O
consortium	O
of	O
manufacturers	O
(	O
Sony	O
,	O
Philips	O
,	O
Toshiba	O
,	O
Panasonic	O
)	O
developed	O
the	O
second	O
generation	O
of	O
the	O
optical	B-Device
disc	I-Device
,	O
the	O
DVD	O
.	O
</s>
<s>
Magnetic	B-Architecture
disks	I-Architecture
found	O
limited	O
applications	O
in	O
storing	O
the	O
data	O
in	O
large	O
amount	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
it	O
was	O
found	O
that	O
by	O
using	O
optical	O
means	O
large	O
data	O
storing	O
devices	O
can	O
be	O
made	O
that	O
in	O
turn	O
gave	O
rise	O
to	O
the	O
optical	B-Device
discs	I-Device
.	O
</s>
<s>
The	O
DVD	O
disc	O
appeared	O
after	O
the	O
CD-ROM	B-Device
had	O
become	O
widespread	O
in	O
society	O
.	O
</s>
<s>
The	O
third	O
generation	O
optical	B-Device
disc	I-Device
was	O
developed	O
in	O
2000	O
–	O
2006	O
and	O
was	O
introduced	O
as	O
Blu-ray	O
Disc	O
.	O
</s>
<s>
Blu-ray	O
eventually	O
prevailed	O
in	O
a	O
high	O
definition	O
optical	B-Device
disc	I-Device
format	O
war	O
over	O
a	O
competing	O
format	O
,	O
the	O
HD	B-Operating_System
DVD	I-Operating_System
.	O
</s>
<s>
From	O
the	O
start	O
optical	B-Device
discs	I-Device
were	O
used	O
to	O
store	O
broadcast-quality	O
analog	O
video	O
,	O
and	O
later	O
digital	O
media	O
such	O
as	O
music	O
or	O
computer	O
software	O
.	O
</s>
<s>
One	O
example	O
of	O
high-density	O
data	B-General_Concept
storage	I-General_Concept
capacity	O
,	O
achieved	O
with	O
an	O
infrared	O
laser	O
,	O
is	O
700	O
MB	O
of	O
net	O
user	O
data	O
for	O
a	O
12cm	O
compact	O
disc	O
.	O
</s>
<s>
Other	O
factors	O
that	O
affect	O
data	B-General_Concept
storage	I-General_Concept
density	O
include	O
:	O
the	O
existence	O
of	O
multiple	O
layers	O
of	O
data	O
on	O
the	O
disc	O
,	O
the	O
method	O
of	O
rotation	O
(	O
Constant	B-Device
linear	I-Device
velocity	I-Device
(	O
CLV	O
)	O
,	O
Constant	B-Device
angular	I-Device
velocity	I-Device
(	O
CAV	O
)	O
,	O
or	O
zoned-CAV	O
)	O
,	O
the	O
composition	O
of	O
lands	O
and	O
pits	O
,	O
and	O
how	O
much	O
margin	O
is	O
unused	O
is	O
at	O
the	O
center	O
and	O
the	O
edge	O
of	O
the	O
disc	O
.	O
</s>
<s>
Second-generation	O
optical	B-Device
discs	I-Device
were	O
for	O
storing	O
great	O
amounts	O
of	O
data	O
,	O
including	O
broadcast-quality	O
digital	O
video	O
.	O
</s>
<s>
Third-generation	O
optical	B-Device
discs	I-Device
are	O
used	O
for	O
distributing	O
high-definition	B-Device
video	I-Device
and	O
videogames	O
and	O
support	O
greater	O
data	B-General_Concept
storage	I-General_Concept
capacities	O
,	O
accomplished	O
with	O
short-wavelength	O
visible-light	O
lasers	O
and	O
greater	O
numerical	O
apertures	O
.	O
</s>
<s>
Blu-ray	O
Disc	O
and	O
HD	B-Operating_System
DVD	I-Operating_System
uses	O
blue-violet	O
lasers	O
and	O
focusing	O
optics	O
of	O
greater	O
aperture	O
,	O
for	O
use	O
with	O
discs	O
with	O
smaller	O
pits	O
and	O
lands	O
,	O
thereby	O
greater	O
data	B-General_Concept
storage	I-General_Concept
capacity	O
per	O
layer	O
.	O
</s>
<s>
In	O
practice	O
,	O
the	O
effective	O
multimedia	O
presentation	O
capacity	O
is	O
improved	O
with	O
enhanced	O
video	O
data	B-General_Concept
compression	I-General_Concept
codecs	B-General_Concept
such	O
as	O
H.264/MPEG	B-Application
-4	I-Application
AVC	I-Application
and	O
VC-1	B-Operating_System
.	O
</s>
<s>
The	O
following	O
formats	O
go	O
beyond	O
the	O
current	O
third-generation	O
discs	O
and	O
have	O
the	O
potential	O
to	O
hold	O
more	O
than	O
one	O
terabyte	O
(	O
1	O
TB	O
)	O
of	O
data	O
and	O
at	O
least	O
some	O
are	O
meant	O
for	O
cold	O
data	B-General_Concept
storage	I-General_Concept
in	O
data	B-Operating_System
centers	I-Operating_System
:	O
</s>
<s>
In	O
2004	O
,	O
development	O
of	O
the	O
Holographic	B-Device
Versatile	I-Device
Disc	I-Device
(	O
HVD	O
)	O
commenced	O
,	O
which	O
promised	O
the	O
storage	O
of	O
several	O
terabytes	O
of	O
data	O
per	O
disc	O
.	O
</s>
<s>
Folio	O
Photonics	O
is	O
planning	O
to	O
release	O
high-capacity	O
discs	O
in	O
2024	O
cost	O
of	O
$5	O
per	O
TB	O
,	O
with	O
a	O
roadmap	O
to	O
$1	O
per	O
TB	O
,	O
using	O
80%	O
less	O
power	O
energy	O
than	O
HDD	B-Device
.	O
</s>
<s>
There	O
are	O
numerous	O
formats	O
of	O
optical	O
direct	O
to	O
disk	O
recording	O
devices	O
on	O
the	O
market	O
,	O
all	O
of	O
which	O
are	O
based	O
on	O
using	O
a	O
laser	O
to	O
change	O
the	O
reflectivity	O
of	O
the	O
digital	O
recording	O
medium	O
in	O
order	O
to	O
duplicate	O
the	O
effects	O
of	O
the	O
pits	O
and	O
lands	O
created	O
when	O
a	O
commercial	O
optical	B-Device
disc	I-Device
is	O
pressed	O
.	O
</s>
<s>
Formats	O
such	O
as	O
CD-R	O
and	O
DVD-R	O
are	O
"	O
Write	B-Device
once	I-Device
read	I-Device
many	I-Device
"	O
or	O
write-once	O
,	O
while	O
CD-RW	O
and	O
DVD-RW	O
are	O
rewritable	O
,	O
more	O
like	O
a	O
magnetic	B-Architecture
recording	I-Architecture
hard	B-Device
disk	I-Device
drive	I-Device
(	O
HDD	B-Device
)	O
.	O
</s>
<s>
Media	O
technologies	O
vary	O
,	O
for	O
example	O
,	O
M-DISC	B-Device
media	O
uses	O
a	O
rock-like	O
layer	O
to	O
retain	O
data	O
for	O
longer	O
than	O
conventional	O
recordable	O
media	O
.	O
</s>
<s>
While	O
being	O
read-only	O
compatible	O
with	O
existing	O
DVD	O
and	O
Blu-ray	O
drives	O
,	O
M-DISC	B-Device
media	O
can	O
only	O
be	O
written	O
to	O
using	O
a	O
stronger	O
laser	O
specifically	O
made	O
for	O
this	O
purpose	O
,	O
which	O
is	O
built	O
into	O
fewer	O
optical	O
drive	O
models	O
.	O
</s>
<s>
Optical	B-Device
media	I-Device
can	O
predictively	B-Device
be	O
scanned	O
for	O
errors	O
and	O
media	B-Device
deterioration	I-Device
well	O
before	O
any	O
data	O
becomes	O
unreadable	O
.	O
</s>
<s>
Optical	O
formats	O
include	O
some	O
redundancy	O
for	O
error	B-Error_Name
correction	I-Error_Name
,	O
which	O
works	O
until	O
the	O
amount	O
of	O
error	O
exceeds	O
a	O
threshold	O
.	O
</s>
<s>
Error	O
scanning	O
software	O
includes	O
Nero	O
DiscSpeed	O
,	O
k-probe	O
,	O
Opti	O
Drive	O
Control	O
(	O
formerly	O
"	O
CD	O
speed	O
2000	O
"	O
)	O
and	O
DVD	O
info	O
Pro	O
for	O
Windows	O
,	O
and	O
QPxTool	O
for	O
cross-platform	B-Operating_System
.	O
</s>
<s>
There	O
are	O
different	O
types	O
of	O
error	O
measurements	O
,	O
including	O
so-called	O
"	O
C1	O
"	O
,	O
"	O
C2	B-Device
"	O
and	O
"	O
CU	O
"	O
errors	O
on	O
CDs	O
,	O
and	O
"	O
PI/PO	O
(	O
parity	O
inner/outer	O
)	O
errors	O
"	O
and	O
the	O
more	O
critical	O
"	O
PI/PO	O
failures	O
"	O
on	O
DVDs	O
.	O
</s>
<s>
"	O
CU	O
"	O
and	O
"	O
POF	O
"	O
represent	O
uncorrectable	O
errors	O
on	O
data	O
CDs	O
and	O
DVDs	O
respectively	O
,	O
thus	O
data	B-General_Concept
loss	I-General_Concept
,	O
and	O
can	O
be	O
a	O
result	O
of	O
too	O
many	O
consecutive	O
smaller	O
errors	O
.	O
</s>
<s>
Due	O
to	O
the	O
weaker	O
error	B-Error_Name
correction	I-Error_Name
used	O
on	O
Audio	O
CDs	O
(	O
Red	O
Book	O
standard	O
)	O
and	O
Video	O
CDs	O
(	O
White	O
Book	O
standard	O
)	O
,	O
C2	B-Device
errors	I-Device
already	O
lead	O
to	O
data	B-General_Concept
loss	I-General_Concept
.	O
</s>
<s>
However	O
,	O
even	O
with	O
C2	B-Device
errors	I-Device
,	O
the	O
damage	O
is	O
inaudible	O
to	O
some	O
extent	O
.	O
</s>
<s>
Optical	B-Device
discs	I-Device
are	O
made	O
using	O
replication	B-Device
.	O
</s>
<s>
In	O
replication	B-Device
,	O
a	O
cleanroom	B-Application
with	O
yellow	O
light	O
is	O
necessary	O
to	O
protect	O
the	O
light-sensitive	O
photoresist	O
and	O
to	O
prevent	O
dust	O
from	O
corrupting	O
the	O
data	O
on	O
the	O
disc	O
.	O
</s>
<s>
A	O
glass	B-Device
master	I-Device
is	O
used	O
in	O
replication	B-Device
.	O
</s>
<s>
The	O
negative	O
is	O
now	O
a	O
stamper	O
-	O
a	O
part	O
of	O
the	O
mold	O
that	O
will	O
be	O
used	O
for	O
replication	B-Device
.	O
</s>
<s>
Recordable	O
discs	O
add	O
a	O
dye	O
layer	O
,	O
and	O
rewritable	O
discs	O
add	O
a	O
phase	O
change	O
alloy	B-Application
layer	O
instead	O
,	O
which	O
is	O
protected	O
by	O
upper	O
and	O
lower	O
dielectric	O
(	O
electrically	O
insulating	O
)	O
layers	O
.	O
</s>
<s>
This	O
leaves	O
the	O
data	O
in	O
the	O
middle	O
of	O
the	O
disc	O
,	O
which	O
is	O
necessary	O
for	O
DVDs	O
to	O
achieve	O
their	O
storage	B-General_Concept
capacity	I-General_Concept
.	O
</s>
<s>
CD-RW	O
,	O
DVD-RW	O
and	O
DVD+RW	O
receive	O
a	O
metal	O
alloy	B-Application
layer	O
sandwiched	O
between	O
2	O
dielectric	O
layers	O
.	O
</s>
<s>
HD-DVD	B-Operating_System
is	O
made	O
in	O
the	O
same	O
way	O
as	O
DVD	O
.	O
</s>
<s>
The	O
grooves	O
contain	O
a	O
wobble	B-Device
frequency	I-Device
that	O
is	O
used	O
to	O
locate	O
the	O
position	O
of	O
the	O
reading	O
or	O
writing	O
laser	O
on	O
the	O
disc	O
.	O
</s>
<s>
First	O
,	O
a	O
silicon	B-Architecture
wafer	I-Architecture
is	O
used	O
instead	O
of	O
a	O
glass	B-Device
master	I-Device
.	O
</s>
<s>
The	O
wafer	B-Architecture
is	O
processed	O
in	O
the	O
same	O
way	O
a	O
glass	B-Device
master	I-Device
would	O
.	O
</s>
<s>
The	O
wafer	B-Architecture
is	O
then	O
electroplated	O
to	O
form	O
a	O
300-micron	O
thick	O
nickel	O
stamper	O
,	O
which	O
is	O
peeled	O
off	O
from	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
If	O
the	O
discs	O
being	O
produced	O
are	O
BD-Rs	B-Operating_System
or	O
BD-REs	B-Operating_System
,	O
the	O
mold	O
is	O
fitted	O
with	O
a	O
stamper	O
that	O
stamps	O
a	O
groove	O
pattern	O
onto	O
the	O
discs	O
,	O
in	O
lieu	O
of	O
the	O
pits	O
and	O
lands	O
found	O
on	O
BD-ROM	O
discs	O
.	O
</s>
<s>
After	O
cooling	O
,	O
a	O
35	O
nanometre-thick	O
layer	O
of	O
silver	O
alloy	B-Application
is	O
applied	O
to	O
the	O
disc	O
using	O
sputtering	O
.	O
</s>
<s>
Then	O
,	O
a	O
30	O
nanometre-thick	O
layer	O
of	O
silver	O
alloy	B-Application
is	O
then	O
sputtered	O
onto	O
the	O
disc	O
and	O
the	O
process	O
is	O
repeated	O
as	O
many	O
times	O
as	O
required	O
.	O
</s>
<s>
BD-R	B-Operating_System
and	O
BD-RE	B-Operating_System
discs	O
receive	O
(	O
through	O
sputtering	O
)	O
a	O
metal	O
(	O
recording	O
layer	O
)	O
alloy	B-Application
(	O
that	O
is	O
sandwiched	O
between	O
two	O
dielectric	O
layers	O
,	O
also	O
sputtered	O
,	O
in	O
BD-RE	B-Operating_System
)	O
,	O
before	O
receiving	O
the	O
30	O
nanometre	O
metallization	O
(	O
silver	O
alloy	B-Application
,	O
aluminum	O
or	O
gold	O
)	O
layer	O
,	O
which	O
is	O
sputtered	O
.	O
</s>
<s>
Alternatively	O
,	O
the	O
silver	O
alloy	B-Application
may	O
be	O
applied	O
before	O
the	O
recording	O
layer	O
is	O
applied	O
.	O
</s>
<s>
Silver	O
alloys	B-Application
are	O
usually	O
used	O
in	O
Blu-rays	O
,	O
and	O
aluminum	O
is	O
usually	O
used	O
on	O
CDs	O
and	O
DVDs	O
.	O
</s>
<s>
Gold	O
is	O
used	O
in	O
some	O
"	O
Archival	O
"	O
CDs	O
and	O
DVDs	O
,	O
since	O
it	O
is	O
more	O
chemically	O
inert	O
and	O
resistant	O
to	O
corrosion	O
than	O
aluminum	O
,	O
which	O
corrodes	O
into	O
aluminum	O
oxide	O
,	O
which	O
can	O
be	O
seen	O
in	O
disc	B-Device
rot	I-Device
as	O
transparent	O
patches	O
or	O
dots	O
in	O
the	O
disc	O
,	O
that	O
prevent	O
the	O
disc	O
from	O
being	O
read	O
,	O
since	O
the	O
laser	O
light	O
passes	O
through	O
the	O
disc	O
instead	O
of	O
being	O
reflected	O
back	O
into	O
the	O
laser	O
pickup	O
assembly	O
to	O
be	O
read	O
.	O
</s>
<s>
In	O
replication	B-Device
,	O
the	O
process	O
explained	O
above	O
is	O
used	O
to	O
make	O
the	O
discs	O
,	O
while	O
in	O
duplication	O
,	O
CD-R	O
,	O
DVD-R	O
or	O
BD-R	B-Operating_System
discs	O
are	O
recorded	O
and	O
finalized	O
to	O
prevent	O
further	O
recording	O
and	O
allow	O
for	O
wider	O
compatibility	O
.	O
</s>
<s>
(	O
See	O
Optical	B-Application
disc	I-Application
authoring	I-Application
)	O
.	O
</s>
<s>
The	O
equipment	O
is	O
also	O
different	O
:	O
replication	B-Device
is	O
carried	O
out	O
by	O
fully	O
automated	O
purpose-built	O
machinery	O
whose	O
cost	O
is	O
in	O
the	O
hundreds	O
of	O
thousands	O
of	O
US	O
dollars	O
in	O
the	O
used	O
market	O
,	O
while	O
duplication	O
can	O
be	O
automated	O
(	O
using	O
what	O
's	O
known	O
as	O
an	O
autoloader	O
)	O
or	O
be	O
done	O
by	O
hand	O
,	O
and	O
only	O
requires	O
a	O
small	O
tabletop	O
duplicator	O
.	O
</s>
