<s>
The	O
Break	B-Device
key	I-Device
(	O
or	O
the	O
symbol	O
⎉	B-Device
)	O
of	O
a	O
computer	B-Device
keyboard	I-Device
refers	O
to	O
breaking	O
a	O
telegraph	O
circuit	O
and	O
originated	O
with	O
19th	O
century	O
practice	O
.	O
</s>
<s>
In	O
modern	O
usage	O
,	O
the	O
key	O
has	O
no	O
well-defined	O
purpose	O
,	O
but	O
while	O
this	O
is	O
the	O
case	O
,	O
it	O
can	O
be	O
used	O
by	O
software	O
for	O
miscellaneous	O
tasks	O
,	O
such	O
as	O
to	O
switch	O
between	O
multiple	O
login	O
sessions	O
,	O
to	O
terminate	O
a	O
program	O
,	O
or	O
to	O
interrupt	B-Application
a	O
modem	O
connection	O
.	O
</s>
<s>
Because	O
the	O
break	B-Device
function	O
is	O
usually	O
combined	O
with	O
the	O
pause	O
function	O
on	O
one	O
key	O
since	O
the	O
introduction	O
of	O
the	O
IBM	B-Device
Model	I-Device
M	I-Device
101-key	O
keyboard	B-Device
in	O
1985	O
,	O
the	O
Break	B-Device
key	I-Device
is	O
also	O
called	O
the	O
Pause	B-Device
key	I-Device
.	O
</s>
<s>
As	O
a	O
consequence	O
,	O
the	O
receiving	O
operator	O
could	O
interrupt	B-Application
the	O
sending	O
operator	O
by	O
opening	O
their	O
key	O
,	O
breaking	O
the	O
circuit	O
and	O
forcing	O
it	O
into	O
a	O
"	O
spacing	O
"	O
condition	O
.	O
</s>
<s>
(	O
A	O
physical	O
break	B-Device
in	O
the	O
telegraph	O
line	O
would	O
have	O
the	O
same	O
effect	O
.	O
)	O
</s>
<s>
Holding	O
down	O
a	O
special	O
"	O
break	B-Device
"	O
key	O
opened	O
the	O
loop	O
,	O
forcing	O
it	O
into	O
a	O
continuous	O
logic	O
0	O
,	O
or	O
"	O
spacing	O
"	O
,	O
condition	O
.	O
</s>
<s>
When	O
this	O
occurred	O
,	O
the	O
teleprinter	O
mechanisms	O
continually	O
actuated	O
without	O
printing	O
anything	O
,	O
as	O
the	O
all-0s	O
character	O
is	O
the	O
non-printing	O
NUL	O
in	O
both	O
Baudot	O
and	O
ASCII	B-Protocol
.	O
</s>
<s>
This	O
practice	O
carried	O
over	O
to	O
teleprinter	O
use	O
on	O
time-sharing	B-General_Concept
computers	O
.	O
</s>
<s>
The	O
computer	O
(	O
specifically	O
the	O
UART	O
)	O
recognized	O
this	O
as	O
a	O
special	O
"	O
break	B-Device
"	O
condition	O
and	O
generated	O
an	O
interrupt	B-Application
that	O
typically	O
stopped	O
a	O
running	O
program	O
or	O
forced	O
the	O
operating	O
system	O
to	O
prompt	O
for	O
a	O
login	O
.	O
</s>
<s>
On	O
the	O
ZX80	B-Operating_System
and	O
ZX81	O
computers	O
,	O
the	O
Break	B-Device
is	O
accessed	O
by	O
pressing	O
.	O
</s>
<s>
On	O
the	O
ZX	B-Operating_System
Spectrum	I-Operating_System
it	O
is	O
accessed	O
by	O
.	O
</s>
<s>
It	O
does	O
not	O
trigger	O
an	O
interrupt	B-Application
but	O
will	O
halt	O
any	O
running	O
BASIC	O
program	O
,	O
or	O
terminate	O
the	O
loading	O
or	O
saving	O
of	O
data	O
to	O
cassette	O
tape	O
.	O
</s>
<s>
The	O
Sinclair	B-Device
QL	I-Device
computer	O
,	O
without	O
a	O
key	O
,	O
maps	O
the	O
function	O
to	O
.	O
</s>
<s>
On	O
a	O
BBC	B-Device
Micro	I-Device
computer	O
,	O
the	O
key	O
generates	O
a	O
hardware	O
reset	O
which	O
would	O
normally	O
cause	O
a	O
warm	O
restart	O
of	O
the	O
computer	O
.	O
</s>
<s>
If	O
a	O
filing	O
system	O
is	O
installed	O
,	O
will	O
cause	O
the	O
computer	O
to	O
search	O
for	O
and	O
load	O
or	O
run	O
a	O
file	O
called	O
!	O
Boot	B-Operating_System
on	O
the	O
filing	O
system	O
's	O
default	O
device	O
(	O
e.g.	O
</s>
<s>
floppy	O
disk	O
0	O
,	O
network	O
user	O
BOOT	B-Operating_System
)	O
.	O
</s>
<s>
The	O
latter	O
two	O
behaviours	O
were	O
inherited	O
by	O
the	O
successor	O
to	O
Acorn	B-Operating_System
MOS	I-Operating_System
,	O
RISC	B-Operating_System
OS	I-Operating_System
.	O
</s>
<s>
Because	O
of	O
the	O
BBC	B-Device
Micro	I-Device
's	O
near	O
universal	O
usage	O
in	O
British	O
schools	O
,	O
later	O
versions	O
of	O
the	O
machine	O
incorporated	O
a	O
physical	O
lock	O
on	O
the	O
Break	B-Device
key	I-Device
to	O
stop	O
children	O
from	O
intentionally	O
resetting	O
the	O
computer	O
.	O
</s>
<s>
On	O
many	O
modern	O
PCs	B-Device
,	O
interrupts	B-Application
screen	O
output	O
by	O
BIOS	B-Operating_System
until	O
another	O
key	O
is	O
pressed	O
.	O
</s>
<s>
This	O
is	O
effective	O
during	O
boot	B-Operating_System
in	O
text	B-Application
mode	I-Application
and	O
in	O
a	O
DOS	B-Device
box	O
in	O
Windows	B-Application
safe	O
mode	O
with	O
50	O
lines	O
.	O
</s>
<s>
On	O
early	O
keyboards	B-Device
without	O
a	O
key	O
(	O
before	O
the	O
introduction	O
of	O
101/102	O
-key	O
keyboards	B-Device
)	O
the	O
Pause	O
function	O
was	O
assigned	O
to	O
,	O
and	O
the	O
Break	B-Device
function	O
to	O
;	O
these	O
key-combinations	O
still	O
work	O
with	O
most	O
programs	O
,	O
even	O
on	O
modern	O
PCs	B-Device
with	O
modern	O
keyboards	B-Device
.	O
</s>
<s>
Pressing	O
the	O
dedicated	O
key	O
on	O
101/102	O
-key	O
keyboards	B-Device
sends	O
the	O
same	O
scancodes	O
as	O
pressing	O
,	O
then	O
,	O
then	O
releasing	O
them	O
in	O
the	O
reverse	O
order	O
would	O
do	O
;	O
additionally	O
,	O
an	O
E1hex	O
prefix	O
is	O
sent	O
,	O
which	O
enables	O
101/102	O
-key-aware	O
software	O
to	O
discern	O
the	O
two	O
situations	O
,	O
while	O
older	O
software	O
usually	O
just	O
ignores	O
the	O
prefix	O
.	O
</s>
<s>
On	O
modern	O
keyboards	B-Device
,	O
the	O
key	O
is	O
usually	O
labeled	O
Pause	O
with	O
Break	B-Device
below	O
,	O
sometimes	O
separated	O
by	O
a	O
line	O
:	O
,	O
or	O
Pause	O
on	O
the	O
top	O
of	O
the	O
keycap	O
and	O
Break	B-Device
on	O
the	O
front	O
,	O
or	O
only	O
Pause	O
without	O
Break	B-Device
at	O
all	O
.	O
</s>
<s>
In	O
most	O
Windows	B-Application
environments	O
,	O
the	O
key	O
combination	O
brings	O
up	O
the	O
system	O
properties	O
.	O
</s>
<s>
Compact	O
and	O
notebook	O
keyboards	B-Device
often	O
do	O
not	O
have	O
a	O
dedicated	O
key	O
.	O
</s>
<s>
on	O
certain	O
Logitech	O
(	O
LOGI	O
)	O
keyboards	B-Device
.	O
</s>
<s>
For	O
some	O
Dell	O
laptops	O
,	O
without	O
a	O
key	O
,	O
press	O
the	O
and	O
select	O
"	O
Interrupt	B-Application
"	O
.	O
</s>
<s>
While	O
both	O
and	O
combination	O
are	O
commonly	O
implemented	O
as	O
a	O
way	O
of	O
breaking	O
the	O
execution	O
of	O
a	O
console	O
application	O
,	O
they	O
are	O
also	O
used	O
for	O
similar	O
effect	O
in	O
integrated	B-Application
development	I-Application
environments	I-Application
.	O
</s>
<s>
miscellaneous	O
DOS	B-Device
variants	O
)	O
is	O
detected	O
only	O
at	O
the	O
time	O
OS	O
tries	O
reading	O
from	O
a	O
keyboard	B-Device
buffer	O
and	O
only	O
if	O
it	O
's	O
the	O
only	O
key	O
sequence	O
in	O
the	O
buffer	O
,	O
while	O
is	O
often	O
translated	O
instantly	O
(	O
e.g.	O
</s>
<s>
by	O
INT	B-Device
1Bh	I-Device
under	O
DOS	B-Device
)	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
is	O
usually	O
a	O
more	O
effective	O
choice	O
under	O
these	O
operating	O
systems	O
;	O
sensitivity	O
for	O
these	O
two	O
combinations	O
can	O
be	O
enhanced	O
by	O
the	O
BREAK	B-Device
=	O
ON	O
CONFIG.SYS	B-Device
statement	O
.	O
</s>
