<s>
Eight-to-fourteen	B-Protocol
modulation	I-Protocol
(	O
EFM	O
)	O
is	O
a	O
data	O
encoding	O
technique	O
–	O
formally	O
,	O
a	O
line	B-Protocol
code	I-Protocol
–	O
used	O
by	O
compact	O
discs	O
(	O
CD	O
)	O
,	O
laserdiscs	O
(	O
LD	O
)	O
and	O
pre-Hi-MD	O
MiniDiscs	O
.	O
</s>
<s>
EFMPlus	B-Protocol
is	O
a	O
related	O
code	O
,	O
used	O
in	O
DVDs	O
and	O
Super	O
Audio	O
CDs	O
(	O
SACDs	O
)	O
.	O
</s>
<s>
EFM	O
and	O
EFMPlus	B-Protocol
were	O
both	O
invented	O
by	O
Kees	O
A	O
.	O
Schouhamer	O
Immink	O
.	O
</s>
<s>
EFM	O
belongs	O
to	O
the	O
class	O
of	O
DC-free	O
run-length	B-Protocol
limited	I-Protocol
(	O
RLL	B-Protocol
)	O
codes	O
;	O
these	O
have	O
the	O
following	O
two	O
properties	O
:	O
</s>
<s>
Each	O
eight-bit	O
block	O
is	O
translated	O
into	O
a	O
corresponding	O
fourteen-bit	O
codeword	O
using	O
a	O
lookup	B-Data_Structure
table	I-Data_Structure
.	O
</s>
<s>
EFMPlus	B-Protocol
is	O
the	O
channel	O
code	O
used	O
in	O
DVDs	O
and	O
SACDs	O
.	O
</s>
<s>
The	O
EFMPlus	B-Protocol
encoder	O
is	O
based	O
on	O
a	O
deterministic	B-General_Concept
finite	I-General_Concept
automaton	I-General_Concept
having	O
four	O
states	O
,	O
which	O
translates	O
eight-bit	O
input	O
words	O
into	O
sixteen-bit	O
codewords	O
.	O
</s>
<s>
EFMPlus	B-Protocol
effectively	O
reduces	O
storage	O
requirements	O
by	O
one	O
channel	O
bit	O
per	O
user	O
byte	O
,	O
increasing	O
storage	O
capacity	O
by	O
1/16	O
=	O
6.25	O
%	O
.	O
</s>
<s>
Decoding	O
of	O
EFMPlus-generated	O
sequences	O
is	O
accomplished	O
by	O
a	O
sliding-block	O
decoder	O
of	O
length	O
two	O
,	O
that	O
is	O
,	O
two	O
consecutive	O
codewords	O
are	O
required	O
to	O
uniquely	O
reconstitute	O
the	O
sequence	O
of	O
input	O
words	O
.	O
</s>
