<s>
In	O
computing	O
,	O
a	O
directory	B-Application
is	O
a	O
file	B-Application
system	I-Application
cataloging	O
structure	O
which	O
contains	O
references	O
to	O
other	O
computer	B-Operating_System
files	I-Operating_System
,	O
and	O
possibly	O
other	O
directories	B-Application
.	O
</s>
<s>
On	O
many	O
computers	O
,	O
directories	B-Application
are	O
known	O
as	O
folders	O
,	O
or	O
drawers	O
,	O
analogous	O
to	O
a	O
workbench	B-Operating_System
or	O
the	O
traditional	O
office	O
filing	O
cabinet	O
.	O
</s>
<s>
The	O
name	O
derives	O
from	O
books	O
like	O
a	O
telephone	O
directory	B-Application
that	O
lists	O
the	O
phone	O
numbers	O
of	O
all	O
the	O
people	O
living	O
in	O
a	O
certain	O
area	O
.	O
</s>
<s>
Files	O
are	O
organized	O
by	O
storing	O
related	O
files	O
in	O
the	O
same	O
directory	B-Application
.	O
</s>
<s>
In	O
a	O
hierarchical	B-Application
file	I-Application
system	I-Application
(	O
that	O
is	O
,	O
one	O
in	O
which	O
files	O
and	O
directories	B-Application
are	O
organized	O
in	O
a	O
manner	O
that	O
resembles	O
a	O
tree	B-Data_Structure
)	O
,	O
a	O
directory	B-Application
contained	O
inside	O
another	O
directory	B-Application
is	O
called	O
a	O
subdirectory	B-Application
.	O
</s>
<s>
The	O
terms	O
parent	O
and	O
child	O
are	O
often	O
used	O
to	O
describe	O
the	O
relationship	O
between	O
a	O
subdirectory	B-Application
and	O
the	O
directory	B-Application
in	O
which	O
it	O
is	O
cataloged	O
,	O
the	O
latter	O
being	O
the	O
parent	O
.	O
</s>
<s>
The	O
top-most	O
directory	B-Application
in	O
such	O
a	O
filesystem	B-Application
,	O
which	O
does	O
not	O
have	O
a	O
parent	O
of	O
its	O
own	O
,	O
is	O
called	O
the	O
root	B-Application
directory	I-Application
.	O
</s>
<s>
The	O
freedesktop.org	B-Application
media	B-Application
type	I-Application
for	O
directories	B-Application
within	O
many	O
Unix	B-Application
systems	I-Application
–	O
including	O
but	O
not	O
limited	O
to	O
systems	O
using	O
GNOME	B-Application
,	O
KDE	B-Language
Plasma	I-Language
5	I-Language
,	O
or	O
ROX	B-Language
Desktop	I-Language
as	O
the	O
desktop	O
environment	O
–	O
is	O
"	O
inode/directory	B-Application
"	O
.	O
</s>
<s>
This	O
is	O
not	O
an	O
IANA	B-Application
registered	I-Application
media	I-Application
type	I-Application
.	O
</s>
<s>
Historically	O
,	O
and	O
even	O
on	O
some	O
modern	O
embedded	B-Architecture
systems	I-Architecture
,	O
the	O
file	B-Application
systems	I-Application
either	O
had	O
no	O
support	O
for	O
directories	B-Application
at	O
all	O
or	O
had	O
only	O
a	O
"	O
flat	O
"	O
directory	B-Architecture
structure	I-Architecture
,	O
meaning	O
subdirectories	B-Application
were	O
not	O
supported	O
;	O
there	O
were	O
only	O
a	O
group	O
of	O
top-level	O
directories	B-Application
,	O
each	O
containing	O
files	O
.	O
</s>
<s>
In	O
modern	O
systems	O
,	O
a	O
directory	B-Application
can	O
contain	O
a	O
mix	O
of	O
files	O
and	O
subdirectories	B-Application
.	O
</s>
<s>
A	O
reference	O
to	O
a	O
location	O
in	O
a	O
directory	B-Application
system	O
is	O
called	O
a	O
path	B-Application
.	O
</s>
<s>
In	O
many	O
operating	B-General_Concept
systems	I-General_Concept
,	O
programs	O
have	O
an	O
associated	O
working	B-Application
directory	I-Application
in	O
which	O
they	O
execute	O
.	O
</s>
<s>
Typically	O
,	O
file	O
names	O
accessed	O
by	O
the	O
program	O
are	O
assumed	O
to	O
reside	O
within	O
this	O
directory	B-Application
if	O
the	O
file	O
names	O
are	O
not	O
specified	O
with	O
an	O
explicit	O
directory	B-Application
name	O
.	O
</s>
<s>
Some	O
operating	B-General_Concept
systems	I-General_Concept
restrict	O
a	O
user	O
's	O
access	O
only	O
to	O
their	O
home	B-Application
directory	I-Application
or	O
project	O
directory	B-Application
,	O
thus	O
isolating	O
their	O
activities	O
from	O
all	O
other	O
users	O
.	O
</s>
<s>
In	O
early	O
versions	O
of	O
Unix	B-Application
the	O
root	B-Application
directory	I-Application
was	O
the	O
home	B-Application
directory	I-Application
of	O
the	O
root	B-Application
user	I-Application
,	O
but	O
modern	O
Unix	B-Application
usually	O
uses	O
another	O
directory	B-Application
such	O
as	O
for	O
this	O
purpose	O
.	O
</s>
<s>
In	O
keeping	O
with	O
Unix	B-Operating_System
philosophy	I-Operating_System
,	O
Unix	B-Application
systems	I-Application
treat	O
directories	B-Application
as	O
a	O
type	O
of	O
file	O
.	O
</s>
<s>
Caveats	O
include	O
not	O
being	O
able	O
to	O
write	O
to	O
a	O
directory	B-Application
file	O
except	O
indirectly	O
by	O
creating	O
,	O
renaming	O
and	O
removing	O
file	B-Application
system	I-Application
objects	O
in	O
the	O
directory	B-Application
and	O
only	O
being	O
able	O
to	O
read	O
from	O
a	O
directory	B-Application
file	O
using	O
directory-specific	O
library	O
routines	O
and	O
system	B-Operating_System
calls	I-Operating_System
that	O
return	O
records	O
,	O
not	O
a	O
byte-stream	O
.	O
</s>
<s>
The	O
name	O
folder	O
,	O
presenting	O
an	O
analogy	O
to	O
the	O
file	O
folder	O
used	O
in	O
offices	O
,	O
and	O
used	O
in	O
a	O
hierarchical	B-Application
file	I-Application
system	I-Application
design	O
for	O
the	O
Electronic	B-Device
Recording	I-Device
Machine	I-Device
,	I-Device
Accounting	I-Device
(	O
ERMA	B-Device
)	O
Mark	O
1	O
published	O
in	O
1958	O
as	O
well	O
as	O
by	O
Xerox	B-Operating_System
Star	I-Operating_System
,	O
is	O
used	O
in	O
almost	O
all	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
 '	O
desktop	O
environments	O
.	O
</s>
<s>
There	O
is	O
a	O
difference	O
between	O
a	O
directory	B-Application
,	O
which	O
is	O
a	O
file	B-Application
system	I-Application
concept	O
,	O
and	O
the	O
graphical	B-Application
user	I-Application
interface	I-Application
metaphor	O
that	O
is	O
used	O
to	O
represent	O
it	O
(	O
a	O
folder	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
Microsoft	B-Application
Windows	I-Application
uses	O
the	O
concept	O
of	O
special	B-General_Concept
folders	I-General_Concept
to	O
help	O
present	O
the	O
contents	O
of	O
the	O
computer	O
to	O
the	O
user	O
in	O
a	O
fairly	O
consistent	O
way	O
that	O
frees	O
the	O
user	O
from	O
having	O
to	O
deal	O
with	O
absolute	O
directory	B-Application
paths	I-Application
,	O
which	O
can	O
vary	O
between	O
versions	O
of	O
Windows	O
,	O
and	O
between	O
individual	O
installations	O
.	O
</s>
<s>
Many	O
operating	B-General_Concept
systems	I-General_Concept
also	O
have	O
the	O
concept	O
of	O
"	O
smart	O
folders	O
"	O
or	O
virtual	O
folders	O
that	O
reflect	O
the	O
results	O
of	O
a	O
file	B-Application
system	I-Application
search	O
or	O
other	O
operation	O
.	O
</s>
<s>
These	O
folders	O
do	O
not	O
represent	O
a	O
directory	B-Application
in	O
the	O
file	O
hierarchy	O
.	O
</s>
<s>
Many	O
email	B-Protocol
clients	I-Protocol
allow	O
the	O
creation	O
of	O
folders	O
to	O
organize	O
email	O
.	O
</s>
<s>
These	O
folders	O
have	O
no	O
corresponding	O
representation	O
in	O
the	O
filesystem	B-Application
structure	O
.	O
</s>
<s>
The	O
term	O
directory	B-Application
refers	O
to	O
the	O
way	O
a	O
structured	O
list	O
of	O
document	O
files	O
and	O
folders	O
are	O
stored	O
on	O
the	O
computer	O
.	O
</s>
<s>
The	O
distinction	O
can	O
be	O
due	O
to	O
the	O
way	O
a	O
directory	B-Application
is	O
accessed	O
;	O
on	O
Unix	B-Application
systems	I-Application
,	O
is	O
usually	O
referred	O
to	O
as	O
a	O
directory	B-Application
when	O
viewed	O
in	O
a	O
command	B-Application
line	I-Application
console	B-Application
,	O
but	O
if	O
accessed	O
through	O
a	O
graphical	O
file	B-Application
manager	I-Application
,	O
users	O
may	O
sometimes	O
call	O
it	O
a	O
folder	O
.	O
</s>
<s>
Operating	B-General_Concept
systems	I-General_Concept
that	O
support	O
hierarchical	O
filesystems	B-Application
(	O
practically	O
all	O
modern	O
ones	O
)	O
implement	O
a	O
form	O
of	O
caching	B-General_Concept
to	O
RAM	B-Architecture
of	O
recent	O
path	B-Application
lookups	O
.	O
</s>
<s>
In	O
the	O
Unix	B-Application
world	O
,	O
this	O
is	O
usually	O
called	O
Directory	B-Application
Name	O
Lookup	O
Cache	B-General_Concept
(	O
DNLC	O
)	O
,	O
although	O
it	O
is	O
called	O
dcache	O
on	O
Linux	B-Application
.	O
</s>
<s>
For	O
local	O
filesystems	B-Application
,	O
DNLC	O
entries	O
normally	O
expire	O
only	O
under	O
pressure	O
from	O
other	O
more	O
recent	O
entries	O
.	O
</s>
<s>
For	O
network	O
file	B-Application
systems	I-Application
a	O
coherence	B-General_Concept
mechanism	I-General_Concept
is	O
necessary	O
to	O
ensure	O
that	O
entries	O
have	O
not	O
been	O
invalidated	O
by	O
other	O
clients	O
.	O
</s>
