<s>
MultiLevel	B-Device
Recording	I-Device
(	O
ML	O
,	O
also	O
known	O
as	O
M-ary	O
)	O
was	O
a	O
technology	O
originally	O
developed	O
by	O
Optex	O
Corporation	O
and	O
promoted	O
by	O
Calimetrics	O
to	O
increase	O
the	O
storage	O
capacity	O
of	O
optical	B-Device
discs	I-Device
.	O
</s>
<s>
Through	O
a	O
combination	O
of	O
proprietary	O
media	O
,	O
recorder	O
,	O
reader	O
and	O
player	O
modifications	O
,	O
Calimetrics	O
proposed	O
that	O
ML	O
could	O
increase	O
the	O
capacity	O
of	O
a	O
CD-ROM	B-Device
,	O
CD-R	O
or	O
CD-RW	O
to	O
2	O
GB	O
,	O
a	O
single-layer	O
DVD	O
,	O
DVD-R	O
,	O
DVD+R	O
,	O
DVD-RW	O
,	O
DVD+RW	O
or	O
DVD-RAM	O
to	O
7.1	O
to	O
10	O
GB	O
and	O
a	O
single-layer	O
Blu-ray	O
Disc	O
(	O
BD	O
)	O
to	O
as	O
much	O
as	O
60	O
GB	O
.	O
</s>
<s>
The	O
codes	O
used	O
in	O
most	O
optical	B-Device
disc	I-Device
systems	O
are	O
binary	O
,	O
meaning	O
that	O
resulting	O
surface	O
has	O
only	O
two	O
states	O
:	O
marks	O
and	O
non-marks	O
.	O
</s>
<s>
The	O
following	O
figure	O
illustrates	O
the	O
EFM	B-Protocol
code	O
used	O
in	O
CDs	O
and	O
DVDs	O
:	O
</s>
<s>
Because	O
the	O
edges	O
are	O
positioned	O
on	O
a	O
grid	O
that	O
is	O
finer	O
than	O
the	O
minimum	O
mark	O
size	O
,	O
EFM	B-Protocol
achieves	O
about	O
1.5	O
bits	O
per	O
minimum-mark	O
,	O
even	O
though	O
it	O
is	O
a	O
binary	O
code	O
.	O
</s>
<s>
MultiLevel	B-Device
recording	I-Device
refers	O
to	O
the	O
use	O
of	O
multiple	O
reflectivity	O
values	O
to	O
encode	O
data	O
onto	O
an	O
optical	B-Device
disc	I-Device
.	O
</s>
<s>
The	O
following	O
figure	O
illustrates	O
a	O
MultiLevel	B-Device
code	O
(	O
note	O
:	O
colors	O
are	O
used	O
only	O
to	O
represent	O
differences	O
in	O
intensity	O
)	O
:	O
</s>
<s>
The	O
8-level	O
code	O
used	O
on	O
the	O
prototype	O
systems	O
is	O
a	O
convolutional	B-Error_Name
code	I-Error_Name
,	O
storing	O
about	O
2.5	O
bits	O
per	O
data	O
cell	O
.	O
</s>
<s>
MultiLevel	B-Device
optical	O
recording	O
is	O
an	O
example	O
of	O
baseband	B-Algorithm
pulse-amplitude	B-Device
modulation	I-Device
.	O
</s>
<s>
While	O
Non-binary	O
,	O
or	O
M-ary	O
,	O
modulation	O
is	O
common	O
in	O
the	O
telecom	O
industry	O
,	O
the	O
technique	O
was	O
originally	O
developed	O
and	O
patented	O
for	O
optical	B-Device
disc	I-Device
recording	O
at	O
Optex	O
Corporation	O
in	O
the	O
early	O
1990s	O
(	O
in	O
conjunction	O
with	O
the	O
University	O
of	O
Rochester	O
)	O
for	O
use	O
with	O
their	O
Electron	O
Trapping	O
Optical	B-Device
Media	I-Device
(	O
ETOM	O
)	O
.	O
</s>
<s>
MultiLevel	B-Device
recording	I-Device
is	O
sometimes	O
confused	O
with	O
multi-layer	O
storage	O
,	O
in	O
which	O
multiple	O
data	O
surfaces	O
are	O
combined	O
into	O
a	O
single	O
disc	O
.	O
</s>
<s>
Multi-layer	O
and	O
multiLevel	B-Device
technique	O
can	O
be	O
combined	O
(	O
as	O
in	O
dual-layer	O
ML-DVD	O
ROM	O
)	O
,	O
where	O
ML-modulation	O
is	O
applied	O
to	O
each	O
individual	O
layer	O
of	O
the	O
disc	O
.	O
</s>
