<s>
On	O
the	O
x86	B-Operating_System
architecture	I-Operating_System
,	O
a	O
double	B-General_Concept
fault	I-General_Concept
exception	B-General_Concept
occurs	O
if	O
the	O
processor	B-General_Concept
encounters	O
a	O
problem	O
while	O
trying	O
to	O
service	O
a	O
pending	O
interrupt	B-Application
or	O
exception	B-General_Concept
.	O
</s>
<s>
An	O
example	O
situation	O
when	O
a	O
double	B-General_Concept
fault	I-General_Concept
would	O
occur	O
is	O
when	O
an	O
interrupt	B-Application
is	O
triggered	O
but	O
the	O
segment	O
in	O
which	O
the	O
interrupt	B-General_Concept
handler	I-General_Concept
resides	O
is	O
invalid	O
.	O
</s>
<s>
If	O
the	O
processor	B-General_Concept
encounters	O
a	O
problem	O
when	O
calling	O
the	O
double	B-General_Concept
fault	I-General_Concept
handler	O
,	O
a	O
triple	B-Error_Name
fault	I-Error_Name
is	O
generated	O
and	O
the	O
processor	B-General_Concept
shuts	O
down	O
.	O
</s>
<s>
As	O
double	B-General_Concept
faults	I-General_Concept
can	O
only	O
happen	O
due	O
to	O
kernel	B-Operating_System
bugs	O
,	O
they	O
are	O
rarely	O
caused	O
by	O
user	B-Operating_System
space	I-Operating_System
programs	O
in	O
a	O
modern	O
protected	B-Application
mode	I-Application
operating	B-General_Concept
system	I-General_Concept
,	O
unless	O
the	O
program	O
somehow	O
gains	O
kernel	B-Operating_System
access	O
(	O
some	O
viruses	O
and	O
also	O
some	O
low-level	O
DOS	B-Device
programs	O
)	O
.	O
</s>
<s>
Other	O
processors	O
like	O
PowerPC	B-Architecture
or	O
SPARC	B-Architecture
generally	O
save	O
state	O
to	O
predefined	O
and	O
reserved	O
machine	O
registers	O
.	O
</s>
<s>
A	O
double	B-General_Concept
fault	I-General_Concept
will	O
then	O
be	O
a	O
situation	O
where	O
another	O
exception	B-General_Concept
happens	O
while	O
the	O
processor	B-General_Concept
is	O
still	O
using	O
the	O
contents	O
of	O
these	O
registers	O
to	O
process	O
the	O
exception	B-General_Concept
.	O
</s>
<s>
SPARC	B-Architecture
processors	O
have	O
four	O
levels	O
of	O
such	O
registers	O
,	O
i.e.	O
</s>
<s>
they	O
have	O
a	O
4-window	B-General_Concept
register	I-General_Concept
system	I-General_Concept
.	O
</s>
