<s>
In	O
computing	O
,	O
triple	B-Error_Name
modular	I-Error_Name
redundancy	I-Error_Name
,	O
sometimes	O
called	O
triple-mode	O
redundancy	O
,	O
(	O
TMR	O
)	O
is	O
a	O
fault-tolerant	B-General_Concept
form	O
of	O
N-modular	O
redundancy	O
,	O
in	O
which	O
three	O
systems	O
perform	O
a	O
process	O
and	O
that	O
result	O
is	O
processed	O
by	O
a	O
majority-voting	O
system	O
to	O
produce	O
a	O
single	O
output	O
.	O
</s>
<s>
The	O
TMR	O
concept	O
can	O
be	O
applied	O
to	O
many	O
forms	O
of	O
redundancy	O
,	O
such	O
as	O
software	O
redundancy	O
in	O
the	O
form	O
of	O
N-version	B-General_Concept
programming	I-General_Concept
,	O
and	O
is	O
commonly	O
found	O
in	O
fault-tolerant	B-General_Concept
computer	I-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Space	O
satellite	O
systems	O
often	O
use	O
TMR	O
,	O
although	O
satellite	O
RAM	O
usually	O
uses	O
Hamming	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
.	O
</s>
<s>
Some	O
ECC	B-General_Concept
memory	I-General_Concept
uses	O
triple	B-Error_Name
modular	I-Error_Name
redundancy	I-Error_Name
hardware	O
(	O
rather	O
than	O
the	O
more	O
common	O
Hamming	B-Error_Name
code	I-Error_Name
)	O
,	O
because	O
triple	B-Error_Name
modular	I-Error_Name
redundancy	I-Error_Name
hardware	O
is	O
faster	O
than	O
Hamming	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
hardware	O
.	O
</s>
<s>
Called	O
repetition	B-Error_Name
code	I-Error_Name
,	O
some	O
communication	O
systems	O
use	O
N-modular	O
redundancy	O
as	O
a	O
simple	O
form	O
of	O
forward	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
.	O
</s>
<s>
For	O
example	O
,	O
5-modular	O
redundancy	O
communication	O
systems	O
(	O
such	O
as	O
FlexRay	B-Protocol
)	O
use	O
the	O
majority	O
of	O
5	O
samples	O
–	O
if	O
any	O
2	O
of	O
the	O
5	O
results	O
are	O
erroneous	O
,	O
the	O
other	O
3	O
results	O
can	O
correct	O
and	O
mask	O
the	O
fault	O
.	O
</s>
<s>
Modular	O
redundancy	O
is	O
a	O
basic	O
concept	O
,	O
dating	O
to	O
antiquity	O
,	O
while	O
the	O
first	O
use	O
of	O
TMR	O
in	O
a	O
computer	O
was	O
the	O
Czechoslovak	O
computer	O
SAPO	B-Device
,	O
in	O
the	O
1950s	O
.	O
</s>
<s>
The	O
number	O
is	O
typically	O
taken	O
to	O
be	O
at	O
least	O
three	O
,	O
so	O
that	O
error	B-Error_Name
correction	I-Error_Name
by	O
majority	O
vote	O
can	O
take	O
place	O
;	O
it	O
is	O
also	O
usually	O
taken	O
to	O
be	O
odd	O
,	O
so	O
that	O
no	O
ties	O
may	O
happen	O
.	O
</s>
<s>
TMR	O
systems	O
should	O
use	O
data	B-Error_Name
scrubbing	I-Error_Name
–	O
rewrite	O
flip-flops	O
periodically	O
–	O
in	O
order	O
to	O
avoid	O
accumulation	O
of	O
errors	O
.	O
</s>
<s>
This	O
can	O
be	O
protected	O
against	O
by	O
applying	O
triple	B-Error_Name
redundancy	I-Error_Name
to	O
the	O
voters	O
themselves	O
.	O
</s>
<s>
In	O
a	O
few	O
TMR	O
systems	O
,	O
such	O
as	O
the	O
Saturn	B-Device
Launch	I-Device
Vehicle	I-Device
Digital	I-Device
Computer	I-Device
and	O
functional	O
triple	B-Error_Name
modular	I-Error_Name
redundancy	I-Error_Name
(	O
FTMR	O
)	O
systems	O
,	O
the	O
voters	O
are	O
also	O
triplicated	O
.	O
</s>
<s>
In	O
such	O
systems	O
there	O
is	O
no	B-Architecture
single	I-Architecture
point	I-Architecture
of	I-Architecture
failure	I-Architecture
.	O
</s>
<s>
Even	O
though	O
only	O
using	O
a	O
single	O
voter	O
brings	O
a	O
single	B-Architecture
point	I-Architecture
of	I-Architecture
failure	I-Architecture
a	O
failed	O
voter	O
will	O
bring	O
down	O
the	O
entire	O
system	O
most	O
TMR	O
systems	O
do	O
not	O
use	O
triplicated	O
voters	O
.	O
</s>
<s>
To	O
use	O
triple	B-Error_Name
modular	I-Error_Name
redundancy	I-Error_Name
,	O
a	O
ship	O
must	O
have	O
at	O
least	O
three	O
chronometers	O
;	O
two	O
chronometers	O
provided	O
dual	B-Error_Name
modular	I-Error_Name
redundancy	I-Error_Name
,	O
allowing	O
a	O
backup	O
if	O
one	O
should	O
cease	O
to	O
work	O
,	O
but	O
not	O
allowing	O
any	O
error	B-Error_Name
correction	I-Error_Name
if	O
the	O
two	O
displayed	O
a	O
different	O
time	O
,	O
since	O
in	O
case	O
of	O
contradiction	O
between	O
the	O
two	O
chronometers	O
,	O
it	O
would	O
be	O
impossible	O
to	O
know	O
which	O
one	O
was	O
wrong	O
(	O
the	O
error	B-Error_Name
detection	I-Error_Name
obtained	O
would	O
be	O
the	O
same	O
of	O
having	O
only	O
one	O
chronometer	O
and	O
checking	O
it	O
periodically	O
)	O
.	O
</s>
<s>
Three	O
chronometers	O
provided	O
triple	B-Error_Name
modular	I-Error_Name
redundancy	I-Error_Name
,	O
allowing	O
error	B-Error_Name
correction	I-Error_Name
if	O
one	O
of	O
the	O
three	O
was	O
wrong	O
,	O
so	O
the	O
pilot	O
would	O
take	O
the	O
average	O
of	O
the	O
two	O
with	O
closer	O
reading	O
(	O
vote	O
for	O
average	O
precision	O
)	O
.	O
</s>
<s>
In	O
Arthur	O
C	O
.	O
Clarke	O
's	O
science	O
fiction	O
novel	O
Rendezvous	B-Application
with	I-Application
Rama	I-Application
,	O
the	O
Ramans	O
make	O
heavy	O
use	O
of	O
triple	B-Error_Name
redundancy	I-Error_Name
.	O
</s>
<s>
In	O
the	O
popular	O
anime	O
Neon	B-Application
Genesis	I-Application
Evangelion	I-Application
,	O
the	O
Magi	O
are	O
a	O
set	O
of	O
three	O
biological	O
supercomputers	O
that	O
must	O
agree	O
with	O
a	O
2/3	O
majority	O
vote	O
before	O
delivering	O
a	O
decision	O
.	O
</s>
