<s>
In	O
computing	O
,	O
a	O
non-maskable	B-General_Concept
interrupt	I-General_Concept
(	O
NMI	O
)	O
is	O
a	O
hardware	O
interrupt	B-Application
that	O
standard	O
interrupt-masking	O
techniques	O
in	O
the	O
system	O
cannot	O
ignore	O
.	O
</s>
<s>
An	O
NMI	O
is	O
often	O
used	O
when	O
response	O
time	O
is	O
critical	O
or	O
when	O
an	O
interrupt	B-Application
should	O
never	O
be	O
disabled	O
during	O
normal	O
system	O
operation	O
.	O
</s>
<s>
Modern	O
computer	B-General_Concept
architectures	I-General_Concept
typically	O
use	O
NMIs	O
to	O
handle	O
non-recoverable	O
errors	O
which	O
need	O
immediate	O
attention	O
.	O
</s>
<s>
Therefore	O
,	O
such	O
interrupts	B-Application
should	O
not	O
be	O
masked	O
in	O
the	O
normal	O
operation	O
of	O
the	O
system	O
.	O
</s>
<s>
These	O
errors	O
include	O
non-recoverable	O
internal	O
system	O
chipset	B-Device
errors	O
,	O
corruption	O
in	O
system	O
memory	O
such	O
as	O
parity	B-Error_Name
and	O
ECC	B-Error_Name
errors	O
,	O
and	O
data	O
corruption	O
detected	O
on	O
system	O
and	O
peripheral	O
buses	O
.	O
</s>
<s>
In	O
such	O
cases	O
,	O
an	O
NMI	O
can	O
execute	O
an	O
interrupt	B-General_Concept
handler	I-General_Concept
that	O
transfers	O
control	O
to	O
a	O
special	O
monitor	O
program	O
.	O
</s>
<s>
This	O
also	O
allows	O
the	O
debugging	O
or	O
diagnosing	O
of	O
computers	O
which	O
appear	O
hung	B-General_Concept
.	O
</s>
<s>
In	O
older	O
architectures	O
,	O
NMIs	O
were	O
used	O
for	O
interrupts	B-Application
which	O
were	O
typically	O
never	O
disabled	O
because	O
of	O
the	O
required	O
response	O
time	O
.	O
</s>
<s>
Examples	O
include	O
the	O
floppy	B-Device
disk	I-Device
controller	O
on	O
the	O
Amstrad	B-Device
PCW	I-Device
,	O
the	O
8087	B-Device
coprocessor	B-General_Concept
on	O
the	O
x86	B-Operating_System
when	O
used	O
in	O
the	O
IBM	B-Device
PC	I-Device
or	O
its	O
compatibles	O
(	O
even	O
though	O
Intel	O
recommended	O
connecting	O
it	O
to	O
a	O
normal	O
interrupt	B-Application
)	O
,	O
and	O
the	O
Low	O
Battery	O
signal	O
on	O
the	O
HP	B-Device
95LX	I-Device
.	O
</s>
<s>
In	O
the	O
original	O
IBM	B-Device
PC	I-Device
,	O
an	O
NMI	O
was	O
triggered	O
if	O
a	O
parity	B-Error_Name
error	I-Error_Name
was	O
detected	O
in	O
system	O
memory	O
,	O
or	O
reported	O
by	O
an	O
external	O
device	O
.	O
</s>
<s>
A	O
BIOS	B-Operating_System
interrupt	B-General_Concept
handler	I-General_Concept
would	O
then	O
translate	O
the	O
program	O
's	O
request	O
to	O
match	O
the	O
hardware	O
that	O
was	O
actually	O
present	O
.	O
</s>
<s>
The	O
SMM	B-Architecture
in	O
the	O
386SL	O
is	O
a	O
better	O
way	O
to	O
do	O
this	O
.	O
</s>
<s>
Typically	O
,	O
this	O
would	O
restore	O
the	O
control	O
registers	O
to	O
known	O
good	O
values	O
stored	O
in	O
ROM	B-Device
,	O
without	O
destroying	O
whatever	O
data	O
that	O
the	O
user	O
might	O
currently	O
have	O
loaded	O
.	O
</s>
<s>
On	O
the	O
Commodore	O
8-bit	O
machines	O
,	O
the	O
key	O
was	O
hooked	O
up	O
directly	O
or	O
indirectly	O
to	O
the	O
NMI	O
line	O
on	O
the	O
6502-series	O
CPU	O
,	O
but	O
the	O
reset	O
would	O
take	O
place	O
only	O
if	O
the	O
NMI	O
handler	O
routine	O
in	O
ROM	B-Device
detected	O
that	O
was	O
also	O
being	O
held	O
down	O
when	O
was	O
struck	O
(	O
this	O
combination	O
being	O
the	O
Commodore	O
version	O
of	O
a	O
three	B-Device
finger	I-Device
salute	I-Device
)	O
.	O
</s>
<s>
Commodore	O
also	O
connected	O
the	O
MOS	B-Device
Technology	I-Device
6526	I-Device
CIA	O
#2	O
in	O
the	O
C64	O
and	O
C128	B-Device
to	O
the	O
processor	O
's	O
NMI	O
line	O
,	O
which	O
was	O
part	O
of	O
the	O
means	O
by	O
which	O
software	O
emulation	O
of	O
the	O
6551	B-Architecture
ACIA	I-Architecture
was	O
accomplished	O
.	O
</s>
<s>
Debugging	O
NMIs	O
have	O
appeared	O
in	O
a	O
number	O
of	O
forms	O
,	O
including	O
the	O
Apple	B-Device
Macintosh	I-Device
's	O
"	B-Application
programmers	I-Application
 '	I-Application
button	I-Application
"	I-Application
,	O
and	O
certain	O
key	O
combinations	O
on	O
Sun	O
workstations	O
.	O
</s>
<s>
With	O
the	O
introduction	O
of	O
Windows	B-Application
2000	I-Application
,	O
Microsoft	O
allowed	O
the	O
use	O
of	O
an	O
NMI	O
to	O
cause	O
a	O
system	O
to	O
either	O
break	O
into	O
a	O
debugger	B-Application
,	O
or	O
dump	O
the	O
contents	O
of	O
memory	O
to	O
disk	O
and	O
reboot	O
.	O
</s>
<s>
Devices	O
which	O
added	O
a	O
button	O
to	O
generate	O
an	O
NMI	O
,	O
such	O
as	O
Romantic	O
Robot	O
's	O
Multiface	B-Device
,	O
were	O
a	O
popular	O
accessory	O
for	O
1980s	O
8-bit	O
and	O
16-bit	O
home	O
computers	O
.	O
</s>
<s>
These	O
peripherals	O
had	O
a	O
small	O
amount	O
of	O
ROM	B-Device
and	O
an	O
NMI	O
button	O
.	O
</s>
<s>
Pressing	O
the	O
button	O
transferred	O
control	O
to	O
the	O
software	O
in	O
the	O
peripheral	O
's	O
ROM	B-Device
,	O
allowing	O
the	O
suspended	O
program	O
to	O
be	O
saved	O
to	O
disk	O
(	O
very	O
useful	O
for	O
tape-based	O
games	O
with	O
no	O
disk	O
support	O
,	O
but	O
also	O
for	O
saving	O
games	O
in	O
progress	O
)	O
,	O
screenshots	O
to	O
be	O
saved	O
or	O
printed	O
,	O
or	O
values	O
in	O
memory	O
to	O
be	O
manipulated	O
—	O
a	O
cheating	O
technique	O
to	O
acquire	O
extra	O
lives	O
,	O
for	O
example	O
.	O
</s>
<s>
Not	O
all	O
computers	O
provide	O
a	O
mechanism	O
for	O
triggering	O
NMIs	O
;	O
however	O
,	O
many	O
machines	O
(	O
typically	O
rackmount	B-Application
servers	O
)	O
provide	O
a	O
physical	O
button	O
specifically	O
for	O
this	O
purpose	O
.	O
</s>
<s>
Miles	O
Gordon	O
Technology	O
's	O
DISCiPLE	B-Device
and	O
+D	B-Device
products	O
for	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
featured	O
an	O
NMI-producing	O
"	O
magic	O
button	O
"	O
.	O
</s>
<s>
Because	O
these	O
NMIs	O
(	O
often	O
referred	O
to	O
as	O
"	O
vblank	O
interrupts	B-Application
"	O
)	O
occur	O
at	O
frequent	O
,	O
regular	O
intervals	O
,	O
code	O
that	O
manipulates	O
game	O
graphics	O
and	O
audio	O
is	O
often	O
executed	O
inside	O
of	O
the	O
NMI	O
handler	O
routine	O
.	O
</s>
<s>
Clearing	O
the	O
7th	O
bit	O
of	O
the	O
PPU	O
's	O
register	B-General_Concept
disables	O
vblank	O
interrupts	B-Application
,	O
and	O
setting	O
it	O
enables	O
them	O
.	O
</s>
