<s>
The	O
0x88	B-General_Concept
chess	O
board	B-General_Concept
representation	I-General_Concept
is	O
a	O
square-centric	O
method	O
of	O
representing	B-General_Concept
the	I-General_Concept
chess	I-General_Concept
board	I-General_Concept
in	O
computer	B-Application
chess	I-Application
programs	I-Application
.	O
</s>
<s>
The	O
number	O
0x88	B-General_Concept
is	O
a	O
hexadecimal	O
integer	O
(	O
136	O
,	O
210	O
,	O
10001000	O
)	O
.	O
</s>
<s>
In	O
the	O
0x88	B-General_Concept
board	B-General_Concept
representation	I-General_Concept
,	O
the	O
layout	O
is	O
spread	O
out	O
to	O
cover	O
an	O
8-by-16	O
board	O
,	O
equal	O
to	O
the	O
size	O
of	O
two	O
adjacent	O
chessboards	O
.	O
</s>
<s>
In	O
hexadecimal	O
notation	O
,	O
legal	O
chess	O
positions	O
(	O
A1-H8	O
)	O
are	O
always	O
below	O
0x88	B-General_Concept
.	O
</s>
<s>
This	O
layout	O
simplifies	O
many	O
computations	O
that	O
chess	B-Application
programs	I-Application
need	O
to	O
perform	O
by	O
allowing	O
bitwise	O
operations	O
instead	O
of	O
comparisons	O
.	O
</s>
<s>
An	O
advantage	O
of	O
the	O
0x88	B-General_Concept
coding	O
scheme	O
is	O
that	O
values	O
can	O
be	O
easily	O
converted	O
between	O
0x88	B-General_Concept
representation	O
and	O
file-rank	O
coordinates	O
using	O
only	O
bitwise	O
operations	O
,	O
which	O
are	O
simple	O
and	O
efficient	O
for	O
computer	O
processors	O
to	O
work	O
with	O
.	O
</s>
<s>
To	O
convert	O
a	O
zero-based	O
file-rank	O
coordinate	O
to	O
0x88	B-General_Concept
value	O
:	O
</s>
<s>
To	O
convert	O
an	O
0x88	B-General_Concept
value	O
to	O
a	O
file-rank	O
coordinate	O
pair	O
:	O
</s>
<s>
Off-the-board	O
detection	O
is	O
a	O
feature	O
of	O
chess	B-Application
programs	I-Application
which	O
determines	O
whether	O
a	O
piece	O
is	O
on	O
or	O
off	O
the	O
legal	O
chess	O
board	O
.	O
</s>
<s>
In	O
0x88	B-General_Concept
,	O
the	O
highest	O
bit	O
of	O
each	O
nibble	O
represents	O
whether	O
a	O
piece	O
is	O
on	O
the	O
board	O
or	O
not	O
.	O
</s>
<s>
If	O
$square	O
AND	O
0x88	B-General_Concept
(	O
or	O
,	O
in	O
binary	O
,	O
0b10001000	O
)	O
is	O
non-zero	O
,	O
then	O
the	O
square	O
is	O
not	O
on	O
the	O
board	O
.	O
</s>
<s>
The	O
difference	O
of	O
valid	O
0x88	B-General_Concept
coordinates	O
A	O
and	O
B	O
is	O
unique	O
with	O
respect	O
to	O
distance	O
and	O
direction	O
,	O
which	O
is	O
not	O
true	O
for	O
classical	O
packed	O
three-bit	O
rank	O
and	O
file	O
coordinates	O
.	O
</s>
<s>
While	O
classical	O
square	O
coordinates	O
in	O
the	O
0	O
–	O
63	O
range	O
require	O
4K-sized	O
tables	O
(	O
64×64	O
)	O
,	O
the	O
0x88	B-General_Concept
difference	O
takes	O
1/16	O
that	O
or	O
256-sized	O
tables	O
—	O
or	O
even	O
16	O
less	O
.	O
</s>
<s>
Though	O
the	O
0x88	B-General_Concept
representation	O
was	O
initially	O
popular	O
,	O
it	O
has	O
been	O
mostly	O
replaced	O
by	O
the	O
system	O
of	O
bitboards	O
.	O
</s>
