<s>
In	O
computing	O
,	O
configuration	B-Protocol
files	I-Protocol
(	O
commonly	O
known	O
simply	O
as	O
config	B-Protocol
files	I-Protocol
)	O
are	O
files	O
used	O
to	O
configure	O
the	O
parameters	O
and	O
initial	O
settings	O
for	O
some	O
computer	B-Application
programs	I-Application
.	O
</s>
<s>
They	O
are	O
used	O
for	O
user	O
applications	B-Application
,	O
server	B-Application
processes	I-Application
and	O
operating	B-General_Concept
system	I-General_Concept
settings	O
.	O
</s>
<s>
Some	O
applications	B-Application
provide	O
tools	O
to	O
create	O
,	O
modify	O
,	O
and	O
verify	O
the	O
syntax	B-Application
of	O
their	O
configuration	B-Protocol
files	I-Protocol
;	O
these	O
sometimes	O
have	O
graphical	O
interfaces	O
.	O
</s>
<s>
For	O
other	O
programs	O
,	O
system	B-Application
administrators	I-Application
may	O
be	O
expected	O
to	O
create	O
and	O
modify	O
files	O
by	O
hand	O
using	O
a	O
text	O
editor	O
,	O
which	O
is	O
possible	O
because	O
many	O
are	O
human-editable	O
plain	O
text	O
files	O
.	O
</s>
<s>
For	O
server	B-Application
processes	I-Application
and	O
operating-system	O
settings	O
,	O
there	O
is	O
often	O
no	O
standard	O
tool	O
,	O
but	O
operating	B-General_Concept
systems	I-General_Concept
may	O
provide	O
their	O
own	O
graphical	O
interfaces	O
such	O
as	O
YaST	B-Device
or	O
debconf	O
.	O
</s>
<s>
Some	O
computer	B-Application
programs	I-Application
only	O
read	O
their	O
configuration	B-Protocol
files	I-Protocol
at	O
startup	B-Operating_System
.	O
</s>
<s>
Others	O
periodically	O
check	O
the	O
configuration	B-Protocol
files	I-Protocol
for	O
changes	O
.	O
</s>
<s>
Users	O
can	O
instruct	O
some	O
programs	O
to	O
re-read	O
the	O
configuration	B-Protocol
files	I-Protocol
and	O
apply	O
the	O
changes	O
to	O
the	O
current	O
process	O
,	O
or	O
indeed	O
to	O
read	O
arbitrary	O
files	O
as	O
a	O
configuration	B-Protocol
file	I-Protocol
.	O
</s>
<s>
Across	O
Unix-like	O
operating	B-General_Concept
systems	I-General_Concept
many	O
different	O
configuration-file	O
formats	O
exist	O
,	O
with	O
each	O
application	O
or	O
service	O
potentially	O
having	O
a	O
unique	O
format	O
,	O
but	O
there	O
is	O
a	O
strong	O
tradition	O
of	O
them	O
being	O
in	O
human-editable	O
plain	O
text	O
,	O
and	O
a	O
simple	O
key	B-Application
–	I-Application
value	I-Application
pair	I-Application
format	O
is	O
common	O
.	O
</s>
<s>
Filename	O
extensions	O
of	O
.cnf	O
,	O
.conf	B-Protocol
,	O
.cfg	B-Protocol
,	O
.cf	O
or	O
.ini	B-Protocol
are	O
often	O
used	O
.	O
</s>
<s>
Often	O
the	O
default	O
configuration	B-Protocol
files	I-Protocol
contain	O
extensive	O
internal	O
documentation	O
in	O
the	O
form	O
of	O
comments	O
and	O
man	B-Protocol
files	I-Protocol
are	O
also	O
typically	O
used	O
to	O
document	O
the	O
format	O
and	O
options	O
available	O
.	O
</s>
<s>
System-wide	O
software	O
often	O
uses	O
configuration	B-Protocol
files	I-Protocol
stored	O
in	O
/etc	B-Application
,	O
while	O
user	O
applications	B-Application
often	O
use	O
a	O
"	O
dotfile	O
"	O
–	O
a	O
file	B-Operating_System
or	O
directory	O
in	O
the	O
home	O
directory	O
prefixed	O
with	O
a	O
period	O
,	O
which	O
in	O
Unix	O
hides	O
the	O
file	B-Operating_System
or	O
directory	O
from	O
casual	O
listing	O
.	O
</s>
<s>
Some	O
configuration	B-Protocol
files	I-Protocol
run	O
a	O
set	O
of	O
commands	O
upon	O
startup	B-Operating_System
.	O
</s>
<s>
See	O
run	B-Device
commands	I-Device
for	O
further	O
details	O
.	O
</s>
<s>
By	O
contrast	O
,	O
IBM	O
's	O
AIX	B-Application
uses	O
an	O
Object	O
Data	O
Manager	O
(	O
ODM	O
)	O
database	O
to	O
store	O
much	O
of	O
its	O
system	O
settings	O
.	O
</s>
<s>
MS-DOS	B-Application
itself	O
primarily	O
relied	O
on	O
just	O
one	O
configuration	B-Protocol
file	I-Protocol
,	O
CONFIG.SYS	B-Device
.	O
</s>
<s>
This	O
was	O
a	O
plain	O
text	O
file	B-Operating_System
with	O
simple	O
key	B-Application
–	I-Application
value	I-Application
pairs	I-Application
(	O
e.g.	O
</s>
<s>
DEVICEHIGH	O
=	O
C:\DOS\ANSI.SYS	O
)	O
until	O
MS-DOS	B-Application
6	O
,	O
which	O
introduced	O
an	O
INI-file	O
style	O
format	O
.	O
</s>
<s>
There	O
was	O
also	O
a	O
standard	O
plain	O
text	O
batch	O
file	B-Operating_System
named	O
AUTOEXEC.BAT	O
that	O
ran	O
a	O
series	O
of	O
commands	O
on	O
boot	B-Operating_System
.	O
</s>
<s>
Both	O
these	O
files	O
were	O
retained	O
up	O
to	O
Windows	O
98SE	O
,	O
which	O
still	O
ran	O
on	O
top	O
of	O
MS-DOS	B-Application
.	O
</s>
<s>
An	O
example	O
CONFIG.SYS	B-Device
for	O
MS-DOS	B-Application
5	O
:	O
</s>
<s>
DOS	O
applications	B-Application
used	O
a	O
wide	O
variety	O
of	O
individual	O
configuration	B-Protocol
files	I-Protocol
,	O
most	O
of	O
them	O
binary	O
,	O
proprietary	O
and	O
undocumented	O
-	O
and	O
there	O
were	O
no	O
common	O
conventions	O
or	O
formats	O
.	O
</s>
<s>
The	O
early	O
Microsoft	B-Application
Windows	I-Application
family	O
of	O
operating	B-General_Concept
systems	I-General_Concept
heavily	O
utilized	O
plain-text	O
INI	B-Protocol
files	I-Protocol
(	O
from	O
"	O
initialization	O
"	O
)	O
.	O
</s>
<s>
These	O
served	O
as	O
the	O
primary	O
mechanism	O
to	O
configure	O
the	O
operating	B-General_Concept
system	I-General_Concept
and	O
application	O
features	O
.	O
</s>
<s>
The	O
APIs	B-General_Concept
to	O
read	O
and	O
write	O
from	O
these	O
still	O
exist	O
in	O
Windows	O
,	O
but	O
after	O
1993	O
,	O
Microsoft	O
began	O
to	O
steer	O
developers	O
away	O
from	O
using	O
INI	B-Protocol
files	I-Protocol
and	O
toward	O
storing	O
settings	O
in	O
the	O
Windows	B-Protocol
Registry	I-Protocol
,	O
a	O
hierarchical	O
database	O
to	O
store	O
configuration	O
settings	O
,	O
which	O
was	O
introduced	O
that	O
year	O
with	O
Windows	B-Device
NT	I-Device
.	O
</s>
<s>
The	O
Property	B-Application
List	I-Application
is	O
the	O
standard	O
configuration	B-Protocol
file	I-Protocol
format	O
in	O
macOS	B-Application
(	O
as	O
well	O
as	O
in	O
iOS	B-Operating_System
,	O
NeXTSTEP	B-Application
,	O
GNUstep	B-Application
and	O
Cocoa	B-Operating_System
applications	B-Application
)	O
.	O
</s>
<s>
It	O
uses	O
the	O
filename	O
extension	O
.plist	B-Application
.	O
</s>
<s>
IBM	O
's	O
OS/2	B-Application
uses	O
a	O
binary	O
format	O
,	O
also	O
with	O
a	O
.INI	B-Protocol
suffix	O
,	O
but	O
this	O
differs	O
from	O
the	O
Windows	O
versions	O
.	O
</s>
<s>
It	O
contains	O
a	O
list	O
of	O
lists	O
of	O
untyped	O
key	B-Application
–	I-Application
value	I-Application
pairs	I-Application
.	O
</s>
<s>
Two	O
files	O
control	O
system-wide	O
settings	O
:	O
OS2.INI	O
and	O
OS2SYS.INI	O
.	O
</s>
<s>
Application	O
developers	O
can	O
choose	O
whether	O
to	O
use	O
them	O
or	O
to	O
create	O
a	O
specific	O
file	B-Operating_System
for	O
their	O
applications	B-Application
.	O
</s>
<s>
A	O
number	O
of	O
general-purpose	O
serialization	B-Application
formats	O
exist	O
that	O
can	O
represent	O
complex	O
data	O
structures	O
in	O
an	O
easily	O
stored	O
format	O
,	O
and	O
these	O
are	O
often	O
used	O
as	O
a	O
basis	O
for	O
configuration	B-Protocol
files	I-Protocol
,	O
particularly	O
in	O
open-source	B-Application
and	O
platform-neutral	B-Operating_System
software	B-Application
applications	I-Application
and	O
libraries	O
.	O
</s>
<s>
The	O
specifications	B-Application
describing	O
these	O
formats	O
are	O
routinely	O
made	O
available	O
to	O
the	O
public	O
,	O
thus	O
increasing	O
the	O
availability	O
of	O
parsers	B-Language
and	O
emitters	O
across	O
programming	O
languages	O
.	O
</s>
<s>
Examples	O
include	O
:	O
JSON	B-General_Concept
,	O
XML	B-Protocol
,	O
and	O
YAML	B-Protocol
.	O
</s>
