<s>
A	O
master-checker	B-Operating_System
is	O
a	O
hardware-supported	O
fault	B-General_Concept
tolerance	I-General_Concept
method	O
for	O
multiprocessor	B-Operating_System
systems	O
,	O
in	O
which	O
two	O
processors	O
,	O
referred	O
to	O
as	O
the	O
master	O
and	O
checker	O
,	O
calculate	O
the	O
same	O
functions	O
in	O
parallel	O
in	O
order	O
to	O
increase	O
the	O
probability	O
that	O
the	O
result	O
is	O
exact	O
.	O
</s>
<s>
The	O
checker-CPU	O
is	O
synchronised	O
at	O
clock	O
level	O
with	O
the	O
master-CPU	O
and	O
processes	O
the	O
same	O
programs	O
as	O
the	O
master	O
.	O
</s>
<s>
Whenever	O
the	O
master-CPU	O
generates	O
an	O
output	O
,	O
the	O
checker-CPU	O
compares	O
this	O
output	O
to	O
its	O
own	O
calculation	O
and	O
in	O
the	O
event	O
of	O
a	O
difference	O
raises	O
a	O
warning	O
.	O
</s>
<s>
The	O
master-checker	B-Operating_System
system	O
generally	O
gives	O
more	O
accurate	O
answers	O
by	O
ensuring	O
that	O
the	O
answer	O
is	O
correct	O
before	O
passing	O
it	O
on	O
to	O
the	O
application	O
requesting	O
the	O
algorithm	O
being	O
completed	O
.	O
</s>
<s>
If	O
the	O
master-CPU	O
is	O
correct	O
95%	O
or	O
more	O
of	O
the	O
time	O
,	O
the	O
power	O
and	O
time	O
used	O
by	O
the	O
checker-CPU	O
to	O
verify	O
answers	O
is	O
wasted	O
.	O
</s>
<s>
Depending	O
on	O
the	O
merit	O
of	O
a	O
correct	O
answer	O
,	O
a	O
checker-CPU	O
may	O
or	O
may	O
not	O
be	O
warranted	O
.	O
</s>
<s>
In	O
order	O
to	O
alleviate	O
some	O
of	O
the	O
cost	O
in	O
these	O
situations	O
,	O
the	O
checker-CPU	O
may	O
be	O
used	O
to	O
calculate	O
something	O
else	O
in	O
the	O
same	O
algorithm	O
,	O
increasing	O
the	O
speed	O
and	O
processing	O
output	O
of	O
the	O
CPU	B-General_Concept
system	O
.	O
</s>
