<s>
In	O
computing	O
,	O
"	O
.bak	B-General_Concept
"	O
is	O
a	O
filename	O
extension	O
commonly	O
used	O
to	O
signify	O
a	O
backup	B-Protocol
copy	I-Protocol
of	O
a	O
file	B-Operating_System
.	O
</s>
<s>
When	O
a	O
program	O
is	O
about	O
to	O
overwrite	O
an	O
existing	O
file	B-Operating_System
(	O
for	O
example	O
,	O
when	O
the	O
user	O
saves	O
the	O
document	O
they	O
are	O
working	O
on	O
)	O
,	O
the	O
program	O
may	O
first	O
make	O
a	O
copy	O
of	O
the	O
existing	O
file	B-Operating_System
,	O
with	O
.bak	B-General_Concept
appended	O
to	O
the	O
filename	O
.	O
</s>
<s>
This	O
common	O
.bak	B-General_Concept
naming	O
scheme	O
makes	O
it	O
possible	O
to	O
retrieve	O
the	O
original	O
contents	O
of	O
the	O
file	B-Operating_System
in	O
case	O
of	O
a	O
failed	O
write	O
that	O
corrupts	O
the	O
file	B-Operating_System
,	O
which	O
could	O
be	O
caused	O
by	O
an	O
operating	B-General_Concept
system	I-General_Concept
crash	I-General_Concept
,	O
power	O
outage	O
,	O
or	O
disk	O
space	O
exhaustion	O
.	O
</s>
<s>
Without	O
the	O
backup	B-Protocol
file	B-Operating_System
,	O
an	O
unsuccessful	O
write	O
event	O
may	O
truncate	O
a	O
file	B-Operating_System
,	O
meaning	O
it	O
cuts	O
off	O
the	O
file	B-Operating_System
at	O
a	O
position	O
,	O
or	O
leaves	O
a	O
blank	O
file	B-Operating_System
.	O
</s>
<s>
In	O
practice	O
,	O
this	O
could	O
cause	O
a	O
written	O
document	O
to	O
become	O
incomplete	O
or	O
get	O
lost	O
,	O
a	O
multimedia	O
project	O
file	B-Operating_System
(	O
e.g.	O
</s>
<s>
In	O
a	O
similar	O
manner	O
,	O
a	O
user	O
may	O
also	O
manually	O
make	O
a	O
copy	O
of	O
the	O
file	B-Operating_System
before	O
the	O
change	O
and	O
append	O
.bak	B-General_Concept
to	O
the	O
filename	O
,	O
or	O
alternatively	O
save	O
revisions	O
into	O
separate	O
files	O
,	O
to	O
facilitate	O
reverting	O
to	O
an	O
earlier	O
revision	O
in	O
case	O
of	O
an	O
error	O
.	O
</s>
<s>
Other	O
naming	O
schemes	O
are	O
also	O
in	O
widespread	O
use	O
:	O
file	B-Operating_System
~	O
,	O
file.orig	O
,	O
file.old	O
,	O
and	O
appended	O
time	O
stamps	O
.	O
</s>
<s>
Database	O
Applications	O
like	O
FoxPro	B-Application
and	O
SQL	B-Application
Server	I-Application
use	O
.bak	B-General_Concept
files	O
to	O
back	B-Protocol
up	I-Protocol
their	O
databases	O
and	O
other	O
applications	O
,	O
like	O
XML	O
shell	O
,	O
create	O
.bak	B-General_Concept
files	O
in	O
their	O
autosave	B-General_Concept
process	O
.	O
</s>
<s>
This	O
is	O
a	O
partial	O
list	O
of	O
applications	O
that	O
generate	O
.bak	B-General_Concept
files	O
(	O
in	O
some	O
cases	O
as	O
an	O
optional	O
configuration	O
setting	O
)	O
:	O
</s>
