<s>
Belle	B-General_Concept
was	O
a	O
chess	B-Application
computer	I-Application
developed	O
by	O
Joe	O
Condon	O
(	O
hardware	O
)	O
and	O
Ken	O
Thompson	O
(	O
software	O
)	O
at	O
Bell	O
Labs	O
.	O
</s>
<s>
It	O
won	O
the	O
ACM	O
North	O
American	O
Computer	B-Application
Chess	I-Application
Championship	O
five	O
times	O
and	O
the	O
1980	O
World	O
Computer	B-Application
Chess	I-Application
Championship	O
.	O
</s>
<s>
It	O
was	O
the	O
first	O
system	O
to	O
win	O
using	O
specialized	O
chess	B-Application
hardware	O
.	O
</s>
<s>
In	O
its	O
final	O
incarnation	O
,	O
Belle	B-General_Concept
used	O
an	O
LSI-11	O
general-purpose	O
computer	O
to	O
coordinate	O
its	O
chess	B-Application
hardware	O
.	O
</s>
<s>
There	O
were	O
three	O
custom	O
boards	O
for	O
move	O
generation	O
,	O
four	O
custom	O
boards	O
for	O
position	O
evaluation	O
,	O
and	O
a	O
microcode	B-Device
implementation	O
of	O
alpha-beta	B-Algorithm
pruning	I-Algorithm
.	O
</s>
<s>
The	O
computer	O
also	O
had	O
one	O
megabyte	O
of	O
memory	B-General_Concept
for	O
storing	O
transposition	B-General_Concept
tables	I-General_Concept
.	O
</s>
<s>
At	O
the	O
end	O
of	O
its	O
career	O
,	O
Belle	B-General_Concept
was	O
donated	O
to	O
the	O
Smithsonian	O
Institution	O
.	O
</s>
<s>
The	O
overall	O
architecture	O
of	O
Belle	B-General_Concept
was	O
used	O
for	O
the	O
initial	O
designs	O
of	O
ChipTest	B-General_Concept
,	O
the	O
progenitor	O
of	O
IBM	B-General_Concept
Deep	I-General_Concept
Blue	I-General_Concept
.	O
</s>
<s>
Following	O
his	O
work	O
on	O
the	O
Unix	B-Application
operating	I-Application
system	I-Application
,	O
Ken	O
Thompson	O
turned	O
his	O
attention	O
to	O
computer	B-Application
chess	I-Application
.	O
</s>
<s>
In	O
summer	O
1972	O
,	O
he	O
began	O
work	O
on	O
a	O
program	O
for	O
the	O
PDP-11	B-Device
,	O
which	O
would	O
eventually	O
become	O
Belle	B-General_Concept
.	O
</s>
<s>
In	O
competition	O
,	O
this	O
early	O
version	O
encouraged	O
Thompson	O
to	O
pursue	O
a	O
brute-force	B-Algorithm
approach	O
when	O
designing	O
Belle	B-General_Concept
's	O
hardware	O
.	O
</s>
<s>
Belle	B-General_Concept
's	O
design	O
underwent	O
many	O
changes	O
throughout	O
its	O
lifetime	O
.	O
</s>
<s>
The	O
initial	O
chess	B-Application
program	O
was	O
rewritten	O
to	O
utilize	O
move-vs-evaluation	O
quiescence	B-General_Concept
search	I-General_Concept
and	O
evaluate	O
positions	O
by	O
prioritizing	O
material	O
advantage	O
.	O
</s>
<s>
Belle	B-General_Concept
also	O
used	O
a	O
transposition	B-General_Concept
table	I-General_Concept
to	O
avoid	O
redundant	O
examinations	O
of	O
positions	O
.	O
</s>
<s>
In	O
1976	O
,	O
Joe	O
Condon	O
implemented	O
a	O
hardware	O
move	O
generator	O
to	O
be	O
used	O
with	O
software	O
version	O
of	O
Belle	B-General_Concept
on	O
the	O
PDP-11	B-Device
.	O
</s>
<s>
A	O
6-bit	O
"	O
from	O
"	O
register	B-General_Concept
searches	O
the	O
board	O
for	O
friendly	O
pieces	O
.	O
</s>
<s>
This	O
offset	O
is	O
combined	O
with	O
the	O
contents	O
of	O
the	O
"	O
from	O
"	O
register	B-General_Concept
and	O
moved	O
to	O
a	O
6-bit	O
"	O
to	O
"	O
register	B-General_Concept
.	O
</s>
<s>
Belle	B-General_Concept
's	O
second	O
generation	O
was	O
completed	O
in	O
1978	O
.	O
</s>
<s>
The	O
move	O
generator	O
had	O
its	O
own	O
stack	B-General_Concept
,	O
which	O
it	O
used	O
to	O
store	O
moves	O
,	O
rather	O
than	O
outputting	O
them	O
to	O
software	O
.	O
</s>
<s>
A	O
hardware	O
implementation	O
of	O
the	O
transposition	O
memory	B-General_Concept
.	O
</s>
<s>
These	O
changes	O
reduced	O
the	O
role	O
of	O
the	O
PDP-11	B-Device
software	O
.	O
</s>
<s>
Now	O
,	O
the	O
software	O
controlled	O
these	O
three	O
devices	O
and	O
ran	O
the	O
alpha-beta	B-Algorithm
pruning	I-Algorithm
algorithm	O
.	O
</s>
<s>
The	O
second	O
generation	O
of	O
Belle	B-General_Concept
could	O
search	O
5,000	O
positions	O
per	O
second	O
.	O
</s>
<s>
Belle	B-General_Concept
's	O
final	O
incarnation	O
was	O
completed	O
in	O
1980	O
.	O
</s>
<s>
The	O
transposition	O
memory	B-General_Concept
was	O
increased	O
to	O
1	O
Mb	O
.	O
</s>
<s>
Belle	B-General_Concept
's	O
alpha-beta	O
algorithm	O
was	O
now	O
implemented	O
in	O
microcode	B-Device
,	O
controlling	O
the	O
move	O
generator	O
,	O
evaluator	O
,	O
and	O
transposition	B-General_Concept
table	I-General_Concept
.	O
</s>
<s>
The	O
third	O
generation	O
of	O
Belle	B-General_Concept
was	O
controlled	O
by	O
an	O
LSI-11	O
computer	O
.	O
</s>
<s>
Ken	O
Thompson	O
's	O
software	O
version	O
of	O
Belle	B-General_Concept
competed	O
in	O
the	O
1972	O
U.S.	O
Open	O
Chess	B-Application
Championship	O
and	O
the	O
1973	O
ACM	O
Computer	B-Application
Chess	I-Application
Championship	O
.	O
</s>
<s>
Over	O
the	O
next	O
year	O
,	O
Belle	B-General_Concept
played	O
several	O
UCSF	O
games	O
and	O
finished	O
3-1	O
in	O
the	O
1974	O
ACM	O
Computer	B-Application
Chess	I-Application
Championship	O
.	O
</s>
<s>
In	O
1978	O
,	O
the	O
second	O
generation	O
of	O
Belle	B-General_Concept
competed	O
at	O
the	O
ACM	O
Computer	B-Application
Chess	I-Application
Championships	O
,	O
winning	O
with	O
a	O
perfect	O
four	O
wins	O
in	O
four	O
games	O
.	O
</s>
<s>
In	O
a	O
pivotal	O
game	O
against	O
Chess	B-Application
4.7	O
,	O
the	O
runner-up	O
,	O
Belle	B-General_Concept
examined	O
5,000	O
positions	O
per	O
second	O
,	O
while	O
Chess	B-Application
4.7	O
examined	O
3,500	O
.	O
</s>
<s>
In	O
1980	O
,	O
the	O
third	O
generation	O
of	O
Belle	B-General_Concept
won	O
the	O
third	O
World	O
Computer	B-Application
Chess	I-Application
Championship	O
in	O
Linz	O
,	O
Austria	O
.	O
</s>
<s>
After	O
four	O
rounds	O
,	O
it	O
had	O
a	O
score	O
of	O
3.5	O
in	O
four	O
games	O
,	O
tied	O
with	O
the	O
Chaos	O
chess	B-Application
machine	O
.	O
</s>
<s>
In	O
a	O
tie-breaker	O
for	O
the	O
world-champion	O
title	O
,	O
Belle	B-General_Concept
broke	O
through	O
Chaos	O
's	O
Alekhine	O
's	O
Defense	O
and	O
went	O
on	O
to	O
declare	O
checkmate	B-Application
in	O
eight	O
moves	O
,	O
winning	O
the	O
game	O
on	O
move	O
41	O
.	O
</s>
<s>
During	O
the	O
game	O
,	O
Belle	B-General_Concept
searched	O
160,000	O
positions	O
per	O
second	O
.	O
</s>
<s>
In	O
1983	O
,	O
Belle	B-General_Concept
competed	O
in	O
the	O
U.S.	O
Open	O
,	O
where	O
it	O
scored	O
8.5	O
points	O
in	O
twelve	O
games	O
with	O
a	O
performance	O
rating	O
of	O
2363	O
.	O
</s>
<s>
Later	O
that	O
year	O
,	O
the	O
USCF	O
awarded	O
Belle	B-General_Concept
the	O
rank	O
of	O
master	O
.	O
</s>
<s>
Because	O
it	O
reached	O
this	O
level	O
before	O
any	O
other	O
chess	B-Application
computer	I-Application
,	O
Belle	B-General_Concept
was	O
awarded	O
the	O
$	O
5,000	O
Fredkin	O
prize	O
.	O
</s>
<s>
Belle	B-General_Concept
's	O
reign	O
ended	O
when	O
it	O
placed	O
sixth	O
in	O
the	O
Fourth	O
World	O
Computer	B-Application
Chess	I-Application
Championship	O
,	O
despite	O
being	O
the	O
favorite	O
to	O
win	O
.	O
</s>
<s>
Because	O
of	O
its	O
ability	O
to	O
generate	O
and	O
analyze	O
many	O
chess	B-Application
positions	O
,	O
Belle	B-General_Concept
represented	O
the	O
brute-force	B-Algorithm
approach	O
to	O
chess	B-Application
computing	O
.	O
</s>
<s>
In	O
the	O
late	O
1970s	O
,	O
Thompson	O
became	O
interested	O
in	O
the	O
limits	O
of	O
this	O
method	O
,	O
playing	O
different	O
versions	O
of	O
Belle	B-General_Concept
against	O
one	O
another	O
.	O
</s>
<s>
For	O
instance	O
,	O
if	O
one	O
Belle	B-General_Concept
computer	O
searches	O
three	O
levels	O
deep	O
,	O
the	O
other	O
might	O
search	O
to	O
four	O
.	O
</s>
<s>
Thompson	O
concluded	O
that	O
for	O
each	O
additional	O
level	O
of	O
search	O
,	O
Belle	B-General_Concept
improved	O
by	O
approximately	O
250	O
rating	O
points	O
.	O
</s>
