<s>
In	O
computing	O
,	O
a	O
file	B-Application
system	I-Application
or	O
filesystem	B-Application
(	O
often	O
abbreviated	O
to	O
fs	O
)	O
is	O
a	O
method	O
and	O
data	O
structure	O
that	O
the	O
operating	B-General_Concept
system	I-General_Concept
uses	O
to	O
control	O
how	O
data	O
is	O
stored	B-General_Concept
and	O
retrieved	O
.	O
</s>
<s>
Without	O
a	O
file	B-Application
system	I-Application
,	O
data	O
placed	O
in	O
a	O
storage	B-General_Concept
medium	I-General_Concept
would	O
be	O
one	O
large	O
body	O
of	O
data	O
with	O
no	O
way	O
to	O
tell	O
where	O
one	O
piece	O
of	O
data	O
stopped	O
and	O
the	O
next	O
began	O
,	O
or	O
where	O
any	O
piece	O
of	O
data	O
was	O
located	O
when	O
it	O
was	O
time	B-Operating_System
to	O
retrieve	O
it	O
.	O
</s>
<s>
Taking	O
its	O
name	O
from	O
the	O
way	O
a	O
paper-based	O
data	O
management	O
system	O
is	O
named	O
,	O
each	O
group	O
of	O
data	O
is	O
called	O
a	O
"	O
file	B-Operating_System
"	O
.	O
</s>
<s>
There	O
are	O
many	O
kinds	O
of	O
file	B-Application
systems	I-Application
,	O
each	O
with	O
unique	O
structure	O
and	O
logic	O
,	O
properties	O
of	O
speed	O
,	O
flexibility	O
,	O
security	O
,	O
size	O
and	O
more	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
have	O
been	O
designed	O
to	O
be	O
used	O
for	O
specific	O
applications	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
ISO	B-Application
9660	I-Application
and	O
UDF	O
file	B-Application
systems	I-Application
are	O
designed	O
specifically	O
for	O
optical	B-Device
discs	I-Device
.	O
</s>
<s>
File	B-Application
systems	I-Application
can	O
be	O
used	O
on	O
many	O
types	O
of	O
storage	B-General_Concept
devices	I-General_Concept
using	O
various	O
media	O
.	O
</s>
<s>
As	O
of	O
2019	O
,	O
hard	B-Device
disk	I-Device
drives	I-Device
have	O
been	O
key	O
storage	B-General_Concept
devices	I-General_Concept
and	O
are	O
projected	O
to	O
remain	O
so	O
for	O
the	O
foreseeable	O
future	O
.	O
</s>
<s>
Other	O
kinds	O
of	O
media	O
that	O
are	O
used	O
include	O
SSDs	B-Device
,	O
magnetic	O
tapes	O
,	O
and	O
optical	B-Device
discs	I-Device
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
such	O
as	O
with	O
tmpfs	B-Application
,	O
the	O
computer	O
's	O
main	O
memory	O
(	O
random-access	B-Architecture
memory	I-Architecture
,	O
RAM	B-Architecture
)	O
is	O
used	O
to	O
create	O
a	O
temporary	O
file	B-Application
system	I-Application
for	O
short-term	O
use	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
are	O
used	O
on	O
local	O
data	B-General_Concept
storage	I-General_Concept
devices	I-General_Concept
;	O
others	O
provide	O
file	B-Application
access	I-Application
via	O
a	O
network	O
protocol	O
(	O
for	O
example	O
,	O
NFS	B-Protocol
,	O
SMB	B-Operating_System
,	O
or	O
9P	B-Operating_System
clients	O
)	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
are	O
"	O
virtual	O
"	O
,	O
meaning	O
that	O
the	O
supplied	O
"	O
files	B-Operating_System
"	O
(	O
called	O
virtual	O
files	B-Operating_System
)	O
are	O
computed	O
on	O
request	O
(	O
such	O
as	O
procfs	B-Application
and	O
sysfs	B-Application
)	O
or	O
are	O
merely	O
a	O
mapping	O
into	O
a	O
different	O
file	B-Application
system	I-Application
used	O
as	O
a	O
backing	O
store	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
manages	O
access	O
to	O
both	O
the	O
content	O
of	O
files	B-Operating_System
and	O
the	O
metadata	O
about	O
those	O
files	B-Operating_System
.	O
</s>
<s>
It	O
is	O
responsible	O
for	O
arranging	O
storage	O
space	O
;	O
reliability	O
,	O
efficiency	O
,	O
and	O
tuning	O
with	O
regard	O
to	O
the	O
physical	O
storage	B-General_Concept
medium	I-General_Concept
are	O
important	O
design	O
considerations	O
.	O
</s>
<s>
Before	O
the	O
advent	O
of	O
computers	O
the	O
term	O
file	B-Application
system	I-Application
was	O
used	O
to	O
describe	O
a	O
method	O
of	O
storing	O
and	O
retrieving	O
paper	O
documents	O
.	O
</s>
<s>
A	O
file	B-Application
system	I-Application
consists	O
of	O
two	O
or	O
three	O
layers	O
.	O
</s>
<s>
The	O
logical	O
file	B-Application
system	I-Application
is	O
responsible	O
for	O
interaction	O
with	O
the	O
user	O
application	O
.	O
</s>
<s>
It	O
provides	O
the	O
application	B-Application
program	I-Application
interface	I-Application
(	O
API	B-Application
)	O
for	O
file	B-Operating_System
operations	O
OPEN	O
,	O
CLOSE	O
,	O
READ	O
,	O
etc.	O
,	O
and	O
passes	O
the	O
requested	O
operation	O
to	O
the	O
layer	O
below	O
it	O
for	O
processing	O
.	O
</s>
<s>
The	O
logical	O
file	B-Application
system	I-Application
"manage[s]	O
open	O
file	B-Operating_System
table	O
entries	O
and	O
per-process	O
file	B-Application
descriptors	I-Application
"	O
.	O
</s>
<s>
This	O
layer	O
provides	O
"	O
file	B-Application
access	I-Application
,	O
directory	B-Application
operations	O
,	O
 [ and ] 	O
security	O
and	O
protection	O
"	O
.	O
</s>
<s>
The	O
second	O
optional	O
layer	O
is	O
the	O
virtual	B-Application
file	I-Application
system	I-Application
.	O
</s>
<s>
"	O
This	O
interface	O
allows	O
support	O
for	O
multiple	O
concurrent	O
instances	O
of	O
physical	O
file	B-Application
systems	I-Application
,	O
each	O
of	O
which	O
is	O
called	O
a	O
file	B-Application
system	I-Application
implementation	O
"	O
.	O
</s>
<s>
The	O
third	O
layer	O
is	O
the	O
physical	O
file	B-Application
system	I-Application
.	O
</s>
<s>
This	O
layer	O
is	O
concerned	O
with	O
the	O
physical	O
operation	O
of	O
the	O
storage	B-General_Concept
device	I-General_Concept
(	O
e.g.	O
</s>
<s>
It	O
processes	O
physical	O
blocks	B-General_Concept
being	O
read	O
or	O
written	O
.	O
</s>
<s>
It	O
handles	O
buffering	O
and	O
memory	B-General_Concept
management	I-General_Concept
and	O
is	O
responsible	O
for	O
the	O
physical	O
placement	O
of	O
blocks	B-General_Concept
in	O
specific	O
locations	O
on	O
the	O
storage	B-General_Concept
medium	I-General_Concept
.	O
</s>
<s>
The	O
physical	O
file	B-Application
system	I-Application
interacts	O
with	O
the	O
device	B-Application
drivers	I-Application
or	O
with	O
the	O
channel	B-Device
to	O
drive	O
the	O
storage	B-General_Concept
device	I-General_Concept
.	O
</s>
<s>
Note	O
:	O
this	O
only	O
applies	O
to	O
file	B-Application
systems	I-Application
used	O
in	O
storage	B-General_Concept
devices	I-General_Concept
.	O
</s>
<s>
File	B-Application
systems	I-Application
allocate	O
space	O
in	O
a	O
granular	O
manner	O
,	O
usually	O
multiple	O
physical	O
units	O
on	O
the	O
device	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
is	O
responsible	O
for	O
organizing	O
files	B-Operating_System
and	O
directories	B-Application
,	O
and	O
keeping	O
track	O
of	O
which	O
areas	O
of	O
the	O
media	O
belong	O
to	O
which	O
file	B-Operating_System
and	O
which	O
are	O
not	O
being	O
used	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
Apple	B-Operating_System
DOS	I-Operating_System
of	O
the	O
early	O
1980s	O
,	O
256-byte	O
sectors	O
on	O
140	O
kilobyte	O
floppy	B-Device
disk	I-Device
used	O
a	O
track/sector	O
map	O
.	O
</s>
<s>
This	O
results	O
in	O
unused	O
space	O
when	O
a	O
file	B-Operating_System
is	O
not	O
an	O
exact	O
multiple	O
of	O
the	O
allocation	O
unit	O
,	O
sometimes	O
referred	O
to	O
as	O
slack	O
space	O
.	O
</s>
<s>
For	O
a	O
512-byte	O
allocation	O
,	O
the	O
average	O
unused	O
space	O
is	O
256	O
bytes	B-Application
.	O
</s>
<s>
The	O
size	O
of	O
the	O
allocation	O
unit	O
is	O
chosen	O
when	O
the	O
file	B-Application
system	I-Application
is	O
created	O
.	O
</s>
<s>
Choosing	O
the	O
allocation	O
size	O
based	O
on	O
the	O
average	O
size	O
of	O
the	O
files	B-Operating_System
expected	O
to	O
be	O
in	O
the	O
file	B-Application
system	I-Application
can	O
minimize	O
the	O
amount	O
of	O
unusable	O
space	O
.	O
</s>
<s>
Choosing	O
an	O
allocation	O
size	O
that	O
is	O
too	O
small	O
results	O
in	O
excessive	O
overhead	O
if	O
the	O
file	B-Application
system	I-Application
will	O
contain	O
mostly	O
very	O
large	O
files	B-Operating_System
.	O
</s>
<s>
File	B-Application
system	I-Application
fragmentation	I-Application
occurs	O
when	O
unused	O
space	O
or	O
single	O
files	B-Operating_System
are	O
not	O
contiguous	O
.	O
</s>
<s>
As	O
a	O
file	B-Application
system	I-Application
is	O
used	O
,	O
files	B-Operating_System
are	O
created	O
,	O
modified	O
and	O
deleted	O
.	O
</s>
<s>
When	O
a	O
file	B-Operating_System
is	O
created	O
,	O
the	O
file	B-Application
system	I-Application
allocates	O
space	O
for	O
the	O
data	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
permit	O
or	O
require	O
specifying	O
an	O
initial	O
space	O
allocation	O
and	O
subsequent	O
incremental	O
allocations	O
as	O
the	O
file	B-Operating_System
grows	O
.	O
</s>
<s>
As	O
files	B-Operating_System
are	O
deleted	O
,	O
the	O
space	O
they	O
were	O
allocated	O
eventually	O
is	O
considered	O
available	O
for	O
use	O
by	O
other	O
files	B-Operating_System
.	O
</s>
<s>
This	O
is	O
free	O
space	O
fragmentation	B-Application
.	O
</s>
<s>
When	O
a	O
file	B-Operating_System
is	O
created	O
and	O
there	O
is	O
not	O
an	O
area	O
of	O
contiguous	O
space	O
available	O
for	O
its	O
initial	O
allocation	O
,	O
the	O
space	O
must	O
be	O
assigned	O
in	O
fragments	O
.	O
</s>
<s>
When	O
a	O
file	B-Operating_System
is	O
modified	O
such	O
that	O
it	O
becomes	O
larger	O
,	O
it	O
may	O
exceed	O
the	O
space	O
initially	O
allocated	O
to	O
it	O
,	O
another	O
allocation	O
must	O
be	O
assigned	O
elsewhere	O
and	O
the	O
file	B-Operating_System
becomes	O
fragmented	B-Application
.	O
</s>
<s>
In	O
some	O
operating	B-General_Concept
systems	I-General_Concept
,	O
a	O
system	B-Application
administrator	I-Application
may	O
use	O
disk	B-Application
quotas	I-Application
to	O
limit	O
the	O
allocation	O
of	O
disk	B-General_Concept
space	I-General_Concept
.	O
</s>
<s>
A	O
filename	O
(	O
or	O
file	B-Operating_System
name	O
)	O
is	O
used	O
to	O
identify	O
a	O
storage	O
location	O
in	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Most	O
file	B-Application
systems	I-Application
have	O
restrictions	O
on	O
the	O
length	B-General_Concept
of	O
filenames	O
.	O
</s>
<s>
In	O
some	O
file	B-Application
systems	I-Application
,	O
filenames	O
are	O
not	O
case	O
sensitive	O
(	O
i.e.	O
,	O
the	O
names	O
MYFILE	O
and	O
myfile	O
refer	O
to	O
the	O
same	O
file	B-Operating_System
in	O
a	O
directory	B-Application
)	O
;	O
in	O
others	O
,	O
filenames	O
are	O
case	O
sensitive	O
(	O
i.e.	O
,	O
the	O
names	O
MYFILE	O
,	O
MyFile	O
,	O
and	O
myfile	O
refer	O
to	O
three	O
separate	O
files	B-Operating_System
that	O
are	O
in	O
the	O
same	O
directory	B-Application
)	O
.	O
</s>
<s>
Most	O
modern	O
file	B-Application
systems	I-Application
allow	O
filenames	O
to	O
contain	O
a	O
wide	O
range	O
of	O
characters	O
from	O
the	O
Unicode	O
character	O
set	O
.	O
</s>
<s>
However	O
,	O
they	O
may	O
have	O
restrictions	O
on	O
the	O
use	O
of	O
certain	O
special	O
characters	O
,	O
disallowing	O
them	O
within	O
filenames	O
;	O
those	O
characters	O
might	O
be	O
used	O
to	O
indicate	O
a	O
device	O
,	O
device	B-Application
type	I-Application
,	O
directory	B-Application
prefix	O
,	O
file	B-Application
path	I-Application
separator	O
,	O
or	O
file	B-Operating_System
type	O
.	O
</s>
<s>
File	B-Application
systems	I-Application
typically	O
have	O
directories	B-Application
(	O
also	O
called	O
folders	O
)	O
which	O
allow	O
the	O
user	O
to	O
group	O
files	B-Operating_System
into	O
separate	O
collections	O
.	O
</s>
<s>
This	O
may	O
be	O
implemented	O
by	O
associating	O
the	O
file	B-Operating_System
name	O
with	O
an	O
index	O
in	O
a	O
table	O
of	O
contents	O
or	O
an	O
inode	B-Application
in	O
a	O
Unix-like	B-Operating_System
file	B-Application
system	I-Application
.	O
</s>
<s>
Directory	B-Architecture
structures	I-Architecture
may	O
be	O
flat	O
(	O
i.e.	O
</s>
<s>
linear	O
)	O
,	O
or	O
allow	O
hierarchies	O
where	O
directories	B-Application
may	O
contain	O
subdirectories	B-Application
.	O
</s>
<s>
The	O
first	O
file	B-Application
system	I-Application
to	O
support	O
arbitrary	O
hierarchies	O
of	O
directories	B-Application
was	O
used	O
in	O
the	O
Multics	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
The	O
native	O
file	B-Application
systems	I-Application
of	O
Unix-like	B-Operating_System
systems	I-Operating_System
also	O
support	O
arbitrary	O
directory	B-Application
hierarchies	O
,	O
as	O
do	O
,	O
for	O
example	O
,	O
Apple	O
's	O
Hierarchical	B-Application
File	I-Application
System	I-Application
and	O
its	O
successor	O
HFS+	B-Application
in	O
classic	B-Application
Mac	I-Application
OS	I-Application
,	O
the	O
FAT	B-Application
file	I-Application
system	I-Application
in	O
MS-DOS	B-Application
2.0	O
and	O
later	O
versions	O
of	O
MS-DOS	B-Application
and	O
in	O
Microsoft	B-Application
Windows	I-Application
,	O
the	O
NTFS	B-Application
file	I-Application
system	I-Application
in	O
the	O
Windows	B-Device
NT	I-Device
family	I-Device
of	O
operating	B-General_Concept
systems	I-General_Concept
,	O
and	O
the	O
ODS-2	O
(	O
On-Disk	O
Structure-2	O
)	O
and	O
higher	O
levels	O
of	O
the	O
Files-11	B-Application
file	B-Application
system	I-Application
in	O
OpenVMS	B-Operating_System
.	O
</s>
<s>
Other	O
bookkeeping	O
information	O
is	O
typically	O
associated	O
with	O
each	O
file	B-Operating_System
within	O
a	O
file	B-Application
system	I-Application
.	O
</s>
<s>
The	O
length	B-General_Concept
of	O
the	O
data	O
contained	O
in	O
a	O
file	B-Operating_System
may	O
be	O
stored	B-General_Concept
as	O
the	O
number	O
of	O
blocks	B-General_Concept
allocated	O
for	O
the	O
file	B-Operating_System
or	O
as	O
a	O
byte	B-Application
count	O
.	O
</s>
<s>
The	O
time	B-Operating_System
that	O
the	O
file	B-Operating_System
was	O
last	O
modified	O
may	O
be	O
stored	B-General_Concept
as	O
the	O
file	B-Operating_System
's	O
timestamp	O
.	O
</s>
<s>
File	B-Application
systems	I-Application
might	O
store	O
the	O
file	B-Operating_System
creation	O
time	B-Operating_System
,	O
the	O
time	B-Operating_System
it	O
was	O
last	O
accessed	O
,	O
the	O
time	B-Operating_System
the	O
file	B-Operating_System
's	O
metadata	O
was	O
changed	O
,	O
or	O
the	O
time	B-Operating_System
the	O
file	B-Operating_System
was	O
last	O
backed	O
up	O
.	O
</s>
<s>
Other	O
information	O
can	O
include	O
the	O
file	B-Operating_System
's	O
device	B-Application
type	I-Application
(	O
e.g.	O
</s>
<s>
block	O
,	O
character	O
,	O
socket	B-Protocol
,	O
subdirectory	B-Application
,	O
etc	O
.	O
</s>
<s>
)	O
,	O
its	O
owner	O
user	B-Application
ID	I-Application
and	O
group	B-Application
ID	I-Application
,	O
its	O
access	O
permissions	O
and	O
other	O
file	B-Application
attributes	I-Application
(	O
e.g.	O
</s>
<s>
whether	O
the	O
file	B-Operating_System
is	O
read-only	O
,	O
executable	B-Application
,	O
etc	O
.	O
</s>
<s>
A	O
file	B-Application
system	I-Application
stores	O
all	O
the	O
metadata	O
associated	O
with	O
the	O
file	B-Operating_System
—	O
including	O
the	O
file	B-Operating_System
name	O
,	O
the	O
length	B-General_Concept
of	O
the	O
contents	O
of	O
a	O
file	B-Operating_System
,	O
and	O
the	O
location	O
of	O
the	O
file	B-Operating_System
in	O
the	O
folder	O
hierarchy	O
—	O
separate	O
from	O
the	O
contents	O
of	O
the	O
file	B-Operating_System
.	O
</s>
<s>
Most	O
file	B-Application
systems	I-Application
store	O
the	O
names	O
of	O
all	O
the	O
files	B-Operating_System
in	O
one	O
directory	B-Application
in	O
one	O
place	O
—	O
the	O
directory	B-Application
table	I-Application
for	O
that	O
directory	B-Application
—	O
which	O
is	O
often	O
stored	B-General_Concept
like	O
any	O
other	O
file	B-Operating_System
.	O
</s>
<s>
Many	O
file	B-Application
systems	I-Application
put	O
only	O
some	O
of	O
the	O
metadata	O
for	O
a	O
file	B-Operating_System
in	O
the	O
directory	B-Application
table	I-Application
,	O
and	O
the	O
rest	O
of	O
the	O
metadata	O
for	O
that	O
file	B-Operating_System
in	O
a	O
completely	O
separate	O
structure	O
,	O
such	O
as	O
the	O
inode	B-Application
.	O
</s>
<s>
Most	O
file	B-Application
systems	I-Application
also	O
store	O
metadata	O
not	O
associated	O
with	O
any	O
one	O
particular	O
file	B-Operating_System
.	O
</s>
<s>
Such	O
metadata	O
includes	O
information	O
about	O
unused	O
regions	O
—	O
free	B-Application
space	I-Application
bitmap	I-Application
,	O
block	B-Application
availability	I-Application
map	I-Application
—	O
and	O
information	O
about	O
bad	B-Device
sectors	I-Device
.	O
</s>
<s>
Often	O
such	O
information	O
about	O
an	O
allocation	B-Application
group	I-Application
is	O
stored	B-General_Concept
inside	O
the	O
allocation	B-Application
group	I-Application
itself	O
.	O
</s>
<s>
Additional	O
attributes	O
can	O
be	O
associated	O
on	O
file	B-Application
systems	I-Application
,	O
such	O
as	O
NTFS	B-Application
,	O
XFS	B-Application
,	O
ext2	B-Application
,	O
ext3	B-Application
,	O
some	O
versions	O
of	O
UFS	B-Operating_System
,	O
and	O
HFS+	B-Application
,	O
using	O
extended	B-Application
file	I-Application
attributes	I-Application
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
provide	O
for	O
user	O
defined	O
attributes	O
such	O
as	O
the	O
author	O
of	O
the	O
document	O
,	O
the	O
character	O
encoding	O
of	O
a	O
document	O
or	O
the	O
size	O
of	O
an	O
image	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
allow	O
for	O
different	O
data	O
collections	O
to	O
be	O
associated	O
with	O
one	O
file	B-Operating_System
name	O
.	O
</s>
<s>
Apple	O
has	O
long	O
used	O
a	O
forked	O
file	B-Application
system	I-Application
on	O
the	O
Macintosh	B-Device
,	O
and	O
Microsoft	O
supports	O
streams	O
in	O
NTFS	B-Application
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
maintain	O
multiple	O
past	O
revisions	O
of	O
a	O
file	B-Operating_System
under	O
a	O
single	O
file	B-Operating_System
name	O
;	O
the	O
filename	O
by	O
itself	O
retrieves	O
the	O
most	O
recent	O
version	O
,	O
while	O
prior	O
saved	O
version	O
can	O
be	O
accessed	O
using	O
a	O
special	O
naming	O
convention	O
such	O
as	O
"	O
filename	O
;	O
4	O
"	O
or	O
"	O
filename(-4 )	O
"	O
to	O
access	O
the	O
version	O
four	O
saves	O
ago	O
.	O
</s>
<s>
See	O
comparison	B-Application
of	I-Application
file	I-Application
systems	I-Application
#Metadata	O
for	O
details	O
on	O
which	O
file	B-Application
systems	I-Application
support	O
which	O
kinds	O
of	O
metadata	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
a	O
file	B-Application
system	I-Application
may	O
not	O
make	O
use	O
of	O
a	O
storage	B-General_Concept
device	I-General_Concept
but	O
can	O
be	O
used	O
to	O
organize	O
and	O
represent	O
access	O
to	O
any	O
data	O
,	O
whether	O
it	O
is	O
stored	B-General_Concept
or	O
dynamically	O
generated	O
(	O
e.g.	O
</s>
<s>
procfs	B-Application
)	O
.	O
</s>
<s>
File	B-Application
systems	I-Application
include	O
utilities	O
to	O
initialize	O
,	O
alter	O
parameters	O
of	O
and	O
remove	O
an	O
instance	O
of	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Some	O
include	O
the	O
ability	O
to	O
extend	O
or	O
truncate	O
the	O
space	O
allocated	O
to	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Directory	B-Application
utilities	O
may	O
be	O
used	O
to	O
create	O
,	O
rename	O
and	O
delete	O
directory	B-Application
entries	O
,	O
which	O
are	O
also	O
known	O
as	O
dentries	O
(	O
singular	O
:	O
dentry	O
)	O
,	O
and	O
to	O
alter	O
metadata	O
associated	O
with	O
a	O
directory	B-Application
.	O
</s>
<s>
Directory	B-Application
utilities	O
may	O
also	O
include	O
capabilities	O
to	O
create	O
additional	O
links	O
to	O
a	O
directory	B-Application
(	O
hard	B-Application
links	I-Application
in	O
Unix	B-Application
)	O
,	O
to	O
rename	O
parent	O
links	O
(".."	O
in	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
)	O
,	O
and	O
to	O
create	O
bidirectional	O
links	O
to	O
files	B-Operating_System
.	O
</s>
<s>
File	B-Operating_System
utilities	O
create	O
,	O
list	O
,	O
copy	O
,	O
move	O
and	O
delete	O
files	B-Operating_System
,	O
and	O
alter	O
metadata	O
.	O
</s>
<s>
They	O
may	O
be	O
able	O
to	O
truncate	O
data	O
,	O
truncate	O
or	O
extend	O
space	O
allocation	O
,	O
append	O
to	O
,	O
move	O
,	O
and	O
modify	O
files	B-Operating_System
in-place	O
.	O
</s>
<s>
Depending	O
on	O
the	O
underlying	O
structure	O
of	O
the	O
file	B-Application
system	I-Application
,	O
they	O
may	O
provide	O
a	O
mechanism	O
to	O
prepend	O
to	O
or	O
truncate	O
from	O
the	O
beginning	O
of	O
a	O
file	B-Operating_System
,	O
insert	O
entries	O
into	O
the	O
middle	O
of	O
a	O
file	B-Operating_System
,	O
or	O
delete	O
entries	O
from	O
a	O
file	B-Operating_System
.	O
</s>
<s>
Utilities	O
to	O
free	O
space	O
for	O
deleted	O
files	B-Operating_System
,	O
if	O
the	O
file	B-Application
system	I-Application
provides	O
an	O
undelete	O
function	O
,	O
also	O
belong	O
to	O
this	O
category	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
defer	O
operations	O
such	O
as	O
reorganization	O
of	O
free	O
space	O
,	O
secure	O
erasing	O
of	O
free	O
space	O
,	O
and	O
rebuilding	O
of	O
hierarchical	O
structures	O
by	O
providing	O
utilities	O
to	O
perform	O
these	O
functions	O
at	O
times	O
of	O
minimal	O
activity	O
.	O
</s>
<s>
An	O
example	O
is	O
the	O
file	B-Application
system	I-Application
defragmentation	B-Application
utilities	O
.	O
</s>
<s>
Some	O
of	O
the	O
most	O
important	O
features	O
of	O
file	B-Application
system	I-Application
utilities	O
are	O
supervisory	O
activities	O
which	O
may	O
involve	O
bypassing	O
ownership	O
or	O
direct	O
access	O
to	O
the	O
underlying	O
device	O
.	O
</s>
<s>
These	O
include	O
high-performance	O
backup	O
and	O
recovery	O
,	O
data	O
replication	O
,	O
and	O
reorganization	O
of	O
various	O
data	O
structures	O
and	O
allocation	O
tables	O
within	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
There	O
are	O
several	O
mechanisms	O
used	O
by	O
file	B-Application
systems	I-Application
to	O
control	O
access	O
to	O
data	O
.	O
</s>
<s>
Usually	O
the	O
intent	O
is	O
to	O
prevent	O
reading	O
or	O
modifying	O
files	B-Operating_System
by	O
a	O
user	O
or	O
group	O
of	O
users	O
.	O
</s>
<s>
Examples	O
include	O
passwords	O
stored	B-General_Concept
in	O
the	O
metadata	O
of	O
the	O
file	B-Operating_System
or	O
elsewhere	O
and	O
file	B-Operating_System
permissions	O
in	O
the	O
form	O
of	O
permission	O
bits	O
,	O
access	O
control	O
lists	O
,	O
or	O
capabilities	O
.	O
</s>
<s>
The	O
need	O
for	O
file	B-Application
system	I-Application
utilities	O
to	O
be	O
able	O
to	O
access	O
the	O
data	O
at	O
the	O
media	O
level	O
to	O
reorganize	O
the	O
structures	O
and	O
provide	O
efficient	O
backup	O
usually	O
means	O
that	O
these	O
are	O
only	O
effective	O
for	O
polite	O
users	O
but	O
are	O
not	O
effective	O
against	O
intruders	O
.	O
</s>
<s>
Methods	O
for	O
encrypting	O
file	B-Operating_System
data	O
are	O
sometimes	O
included	O
in	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
This	O
is	O
very	O
effective	O
since	O
there	O
is	O
no	O
need	O
for	O
file	B-Application
system	I-Application
utilities	O
to	O
know	O
the	O
encryption	O
seed	O
to	O
effectively	O
manage	O
the	O
data	O
.	O
</s>
<s>
One	O
significant	O
responsibility	O
of	O
a	O
file	B-Application
system	I-Application
is	O
to	O
ensure	O
that	O
the	O
file	B-Application
system	I-Application
structures	O
in	O
secondary	O
storage	O
remain	O
consistent	O
,	O
regardless	O
of	O
the	O
actions	O
by	O
programs	O
accessing	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
This	O
includes	O
actions	O
taken	O
if	O
a	O
program	O
modifying	O
the	O
file	B-Application
system	I-Application
terminates	O
abnormally	O
or	O
neglects	O
to	O
inform	O
the	O
file	B-Application
system	I-Application
that	O
it	O
has	O
completed	O
its	O
activities	O
.	O
</s>
<s>
This	O
may	O
include	O
updating	O
the	O
metadata	O
,	O
the	O
directory	B-Application
entry	O
and	O
handling	O
any	O
data	O
that	O
was	O
buffered	O
but	O
not	O
yet	O
updated	O
on	O
the	O
physical	O
storage	B-General_Concept
media	I-General_Concept
.	O
</s>
<s>
Other	O
failures	O
which	O
the	O
file	B-Application
system	I-Application
must	O
deal	O
with	O
include	O
media	O
failures	O
or	O
loss	O
of	O
connection	O
to	O
remote	O
systems	O
.	O
</s>
<s>
In	O
the	O
event	O
of	O
an	O
operating	B-General_Concept
system	I-General_Concept
failure	O
or	O
"	O
soft	O
"	O
power	O
failure	O
,	O
special	O
routines	O
in	O
the	O
file	B-Application
system	I-Application
must	O
be	O
invoked	O
similar	O
to	O
when	O
an	O
individual	O
program	O
fails	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
must	O
also	O
be	O
able	O
to	O
correct	O
damaged	O
structures	O
.	O
</s>
<s>
These	O
may	O
occur	O
as	O
a	O
result	O
of	O
an	O
operating	B-General_Concept
system	I-General_Concept
failure	O
for	O
which	O
the	O
OS	O
was	O
unable	O
to	O
notify	O
the	O
file	B-Application
system	I-Application
,	O
a	O
power	O
failure	O
,	O
or	O
a	O
reset	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
must	O
also	O
record	O
events	O
to	O
allow	O
analysis	O
of	O
systemic	O
issues	O
as	O
well	O
as	O
problems	O
with	O
specific	O
files	B-Operating_System
or	O
directories	B-Application
.	O
</s>
<s>
The	O
most	O
important	O
purpose	O
of	O
a	O
file	B-Application
system	I-Application
is	O
to	O
manage	O
user	O
data	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
accept	O
data	O
for	O
storage	O
as	O
a	O
stream	O
of	O
bytes	B-Application
which	O
are	O
collected	O
and	O
stored	B-General_Concept
in	O
a	O
manner	O
efficient	O
for	O
the	O
media	O
.	O
</s>
<s>
When	O
a	O
program	O
retrieves	O
the	O
data	O
,	O
it	O
specifies	O
the	O
size	O
of	O
a	O
memory	B-General_Concept
buffer	I-General_Concept
and	O
the	O
file	B-Application
system	I-Application
transfers	O
data	O
from	O
the	O
media	O
to	O
the	O
buffer	B-General_Concept
.	O
</s>
<s>
A	O
runtime	O
library	O
routine	O
may	O
sometimes	O
allow	O
the	O
user	O
program	O
to	O
define	O
a	O
record	O
based	O
on	O
a	O
library	O
call	O
specifying	O
a	O
length	B-General_Concept
.	O
</s>
<s>
When	O
the	O
user	O
program	O
reads	O
the	O
data	O
,	O
the	O
library	O
retrieves	O
data	O
via	O
the	O
file	B-Application
system	I-Application
and	O
returns	O
a	O
record	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
allow	O
the	O
specification	O
of	O
a	O
fixed	O
record	O
length	B-General_Concept
which	O
is	O
used	O
for	O
all	O
writes	O
and	O
reads	O
.	O
</s>
<s>
An	O
identification	O
for	O
each	O
record	O
,	O
also	O
known	O
as	O
a	O
key	O
,	O
makes	O
for	O
a	O
more	O
sophisticated	O
file	B-Application
system	I-Application
.	O
</s>
<s>
This	O
requires	O
complicated	O
management	O
of	O
blocks	B-General_Concept
of	O
media	O
usually	O
separating	O
key	O
blocks	B-General_Concept
and	O
data	O
blocks	B-General_Concept
.	O
</s>
<s>
Utilities	O
,	O
language	O
specific	O
run-time	O
libraries	O
and	O
user	O
programs	O
use	O
file	B-Application
system	I-Application
APIs	I-Application
to	O
make	O
requests	O
of	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
These	O
include	O
data	O
transfer	O
,	O
positioning	O
,	O
updating	O
metadata	O
,	O
managing	O
directories	B-Application
,	O
managing	O
access	O
specifications	O
,	O
and	O
removal	O
.	O
</s>
<s>
Frequently	O
,	O
retail	O
systems	O
are	O
configured	O
with	O
a	O
single	O
file	B-Application
system	I-Application
occupying	O
the	O
entire	O
storage	B-General_Concept
device	I-General_Concept
.	O
</s>
<s>
Another	O
approach	O
is	O
to	O
partition	B-Application
the	O
disk	O
so	O
that	O
several	O
file	B-Application
systems	I-Application
with	O
different	O
attributes	O
can	O
be	O
used	O
.	O
</s>
<s>
One	O
file	B-Application
system	I-Application
,	O
for	O
use	O
as	O
browser	O
cache	O
or	O
email	O
storage	O
,	O
might	O
be	O
configured	O
with	O
a	O
small	O
allocation	O
size	O
.	O
</s>
<s>
This	O
keeps	O
the	O
activity	O
of	O
creating	O
and	O
deleting	O
files	B-Operating_System
typical	O
of	O
browser	O
activity	O
in	O
a	O
narrow	O
area	O
of	O
the	O
disk	O
where	O
it	O
will	O
not	O
interfere	O
with	O
other	O
file	B-Operating_System
allocations	O
.	O
</s>
<s>
Another	O
partition	B-Application
might	O
be	O
created	O
for	O
the	O
storage	O
of	O
audio	O
or	O
video	O
files	B-Operating_System
with	O
a	O
relatively	O
large	O
block	B-General_Concept
size	I-General_Concept
.	O
</s>
<s>
A	O
third	O
approach	O
,	O
which	O
is	O
mostly	O
used	O
in	O
cloud	O
systems	O
,	O
is	O
to	O
use	O
"	O
disk	B-Application
images	I-Application
"	O
to	O
house	O
additional	O
file	B-Application
systems	I-Application
,	O
with	O
the	O
same	O
attributes	O
or	O
not	O
,	O
within	O
another	O
(	O
host	O
)	O
file	B-Application
system	I-Application
as	O
a	O
file	B-Operating_System
.	O
</s>
<s>
A	O
common	O
example	O
is	O
virtualization	O
:	O
one	O
user	O
can	O
run	O
an	O
experimental	O
Linux	B-Application
distribution	O
(	O
using	O
the	O
ext4	B-Application
file	B-Application
system	I-Application
)	O
in	O
a	O
virtual	O
machine	O
under	O
his/her	O
production	O
Windows	B-Application
environment	O
(	O
using	O
NTFS	B-Application
)	O
.	O
</s>
<s>
The	O
ext4	B-Application
file	B-Application
system	I-Application
resides	O
in	O
a	O
disk	B-Application
image	I-Application
,	O
which	O
is	O
treated	O
as	O
a	O
file	B-Operating_System
(	O
or	O
multiple	O
files	B-Operating_System
,	O
depending	O
on	O
the	O
hypervisor	B-Operating_System
and	O
settings	O
)	O
in	O
the	O
NTFS	B-Application
host	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Having	O
multiple	O
file	B-Application
systems	I-Application
on	O
a	O
single	O
system	O
has	O
the	O
additional	O
benefit	O
that	O
in	O
the	O
event	O
of	O
a	O
corruption	O
of	O
a	O
single	O
partition	B-Application
,	O
the	O
remaining	O
file	B-Application
systems	I-Application
will	O
frequently	O
still	O
be	O
intact	O
.	O
</s>
<s>
This	O
includes	O
virus	O
destruction	O
of	O
the	O
system	O
partition	B-Application
or	O
even	O
a	O
system	O
that	O
will	O
not	O
boot	B-Operating_System
.	O
</s>
<s>
File	B-Application
system	I-Application
utilities	O
which	O
require	O
dedicated	O
access	O
can	O
be	O
effectively	O
completed	O
piecemeal	O
.	O
</s>
<s>
In	O
addition	O
,	O
defragmentation	B-Application
may	O
be	O
more	O
effective	O
.	O
</s>
<s>
For	O
example	O
,	O
it	O
is	O
not	O
necessary	O
to	O
backup	O
the	O
file	B-Application
system	I-Application
containing	O
videos	O
along	O
with	O
all	O
the	O
other	O
files	B-Operating_System
if	O
none	O
have	O
been	O
added	O
since	O
the	O
last	O
backup	O
.	O
</s>
<s>
As	O
for	O
the	O
image	O
files	B-Operating_System
,	O
one	O
can	O
easily	O
"	O
spin	O
off	O
"	O
differential	O
images	O
which	O
contain	O
only	O
"	O
new	O
"	O
data	O
written	O
to	O
the	O
master	O
(	O
original	O
)	O
image	O
.	O
</s>
<s>
All	O
file	B-Application
systems	I-Application
have	O
some	O
functional	O
limit	O
that	O
defines	O
the	O
maximum	O
storable	O
data	O
capacity	O
within	O
that	O
system	O
.	O
</s>
<s>
These	O
functional	O
limits	O
are	O
a	O
best-guess	O
effort	O
by	O
the	O
designer	O
based	O
on	O
how	O
large	O
the	O
storage	B-General_Concept
systems	I-General_Concept
are	O
right	O
now	O
and	O
how	O
large	O
storage	B-General_Concept
systems	I-General_Concept
are	O
likely	O
to	O
become	O
in	O
the	O
future	O
.	O
</s>
<s>
Disk	O
storage	O
has	O
continued	O
to	O
increase	O
at	O
near	O
exponential	O
rates	O
(	O
see	O
Moore	O
's	O
law	O
)	O
,	O
so	O
after	O
a	O
few	O
years	O
,	O
file	B-Application
systems	I-Application
have	O
kept	O
reaching	O
design	O
limitations	O
that	O
require	O
computer	O
users	O
to	O
repeatedly	O
move	O
to	O
a	O
newer	O
system	O
with	O
ever-greater	O
capacity	O
.	O
</s>
<s>
File	B-Application
system	I-Application
complexity	O
typically	O
varies	O
proportionally	O
with	O
the	O
available	O
storage	B-General_Concept
capacity	I-General_Concept
.	O
</s>
<s>
The	O
file	B-Application
systems	I-Application
of	O
early	O
1980s	O
home	O
computers	O
with	O
50KB	O
to	O
512KB	O
of	O
storage	O
would	O
not	O
be	O
a	O
reasonable	O
choice	O
for	O
modern	O
storage	B-General_Concept
systems	I-General_Concept
with	O
hundreds	O
of	O
gigabytes	O
of	O
capacity	O
.	O
</s>
<s>
Likewise	O
,	O
modern	O
file	B-Application
systems	I-Application
would	O
not	O
be	O
a	O
reasonable	O
choice	O
for	O
these	O
early	O
systems	O
,	O
since	O
the	O
complexity	O
of	O
modern	O
file	B-Application
system	I-Application
structures	O
would	O
quickly	O
consume	O
or	O
even	O
exceed	O
the	O
very	O
limited	O
capacity	O
of	O
the	O
early	O
storage	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
File	B-Application
system	I-Application
types	I-Application
can	O
be	O
classified	O
into	O
disk/tape	O
file	B-Application
systems	I-Application
,	O
network	B-Application
file	I-Application
systems	I-Application
and	O
special-purpose	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
A	O
disk	B-Application
file	I-Application
system	I-Application
takes	O
advantages	O
of	O
the	O
ability	O
of	O
disk	O
storage	B-General_Concept
media	I-General_Concept
to	O
randomly	O
address	O
data	O
in	O
a	O
short	O
amount	O
of	O
time	B-Operating_System
.	O
</s>
<s>
Examples	O
include	O
FAT	B-Application
(	O
FAT12	B-Application
,	O
FAT16	B-Application
,	O
FAT32	B-Application
)	O
,	O
exFAT	B-Application
,	O
NTFS	B-Application
,	O
ReFS	B-Application
,	O
HFS	B-Application
and	O
HFS+	B-Application
,	O
HPFS	B-Application
,	O
APFS	B-Application
,	O
UFS	B-Operating_System
,	O
ext2	B-Application
,	O
ext3	B-Application
,	O
ext4	B-Application
,	O
XFS	B-Application
,	O
btrfs	B-Operating_System
,	O
Files-11	B-Application
,	O
Veritas	B-Application
File	I-Application
System	I-Application
,	O
VMFS	B-Application
,	O
ZFS	B-Application
,	O
ReiserFS	B-Application
and	O
ScoutFS	O
.	O
</s>
<s>
Some	O
disk	B-Application
file	I-Application
systems	I-Application
are	O
journaling	B-Application
file	I-Application
systems	I-Application
or	O
versioning	B-Application
file	I-Application
systems	I-Application
.	O
</s>
<s>
ISO	B-Application
9660	I-Application
and	O
Universal	O
Disk	O
Format	O
(	O
UDF	O
)	O
are	O
two	O
common	O
formats	O
that	O
target	O
Compact	O
Discs	O
,	O
DVDs	O
and	O
Blu-ray	O
discs	O
.	O
</s>
<s>
Mount	B-Device
Rainier	I-Device
is	O
an	O
extension	O
to	O
UDF	O
supported	O
since	O
2.6	O
series	O
of	O
the	O
Linux	B-Application
kernel	O
and	O
since	O
Windows	B-Application
Vista	O
that	O
facilitates	O
rewriting	O
to	O
DVDs	O
.	O
</s>
<s>
A	O
flash	O
file	B-Application
system	I-Application
considers	O
the	O
special	O
abilities	O
,	O
performance	O
and	O
restrictions	O
of	O
flash	B-Device
memory	I-Device
devices	O
.	O
</s>
<s>
Frequently	O
a	O
disk	B-Application
file	I-Application
system	I-Application
can	O
use	O
a	O
flash	B-Device
memory	I-Device
device	O
as	O
the	O
underlying	O
storage	B-General_Concept
media	I-General_Concept
,	O
but	O
it	O
is	O
much	O
better	O
to	O
use	O
a	O
file	B-Application
system	I-Application
specifically	O
designed	O
for	O
a	O
flash	O
device	O
.	O
</s>
<s>
A	O
tape	O
file	B-Application
system	I-Application
is	O
a	O
file	B-Application
system	I-Application
and	O
tape	O
format	O
designed	O
to	O
store	O
files	B-Operating_System
on	O
tape	O
.	O
</s>
<s>
Magnetic	O
tapes	O
are	O
sequential	O
storage	B-General_Concept
media	I-General_Concept
with	O
significantly	O
longer	O
random	O
data	O
access	O
times	O
than	O
disks	O
,	O
posing	O
challenges	O
to	O
the	O
creation	O
and	O
efficient	O
management	O
of	O
a	O
general-purpose	O
file	B-Application
system	I-Application
.	O
</s>
<s>
In	O
a	O
disk	B-Application
file	I-Application
system	I-Application
there	O
is	O
typically	O
a	O
master	O
file	B-Application
directory	I-Application
,	O
and	O
a	O
map	O
of	O
used	O
and	O
free	O
data	O
regions	O
.	O
</s>
<s>
Any	O
file	B-Operating_System
additions	O
,	O
changes	O
,	O
or	O
removals	O
require	O
updating	O
the	O
directory	B-Application
and	O
the	O
used/free	O
maps	O
.	O
</s>
<s>
Consequently	O
,	O
a	O
master	O
file	B-Application
directory	I-Application
and	O
usage	O
map	O
can	O
be	O
extremely	O
slow	O
and	O
inefficient	O
with	O
tape	O
.	O
</s>
<s>
Writing	O
typically	O
involves	O
reading	O
the	O
block	O
usage	O
map	O
to	O
find	O
free	O
blocks	B-General_Concept
for	O
writing	O
,	O
updating	O
the	O
usage	O
map	O
and	O
directory	B-Application
to	O
add	O
the	O
data	O
,	O
and	O
then	O
advancing	O
the	O
tape	O
to	O
write	O
the	O
data	O
in	O
the	O
correct	O
spot	O
.	O
</s>
<s>
Each	O
additional	O
file	B-Operating_System
write	O
requires	O
updating	O
the	O
map	O
and	O
directory	B-Application
and	O
writing	O
the	O
data	O
,	O
which	O
may	O
take	O
several	O
seconds	O
to	O
occur	O
for	O
each	O
file	B-Operating_System
.	O
</s>
<s>
Tape	O
file	B-Application
systems	I-Application
instead	O
typically	O
allow	O
for	O
the	O
file	B-Application
directory	I-Application
to	O
be	O
spread	O
across	O
the	O
tape	O
intermixed	O
with	O
the	O
data	O
,	O
referred	O
to	O
as	O
streaming	O
,	O
so	O
that	O
time-consuming	O
and	O
repeated	O
tape	O
motions	O
are	O
not	O
required	O
to	O
write	O
new	O
data	O
.	O
</s>
<s>
However	O
,	O
a	O
side	O
effect	O
of	O
this	O
design	O
is	O
that	O
reading	O
the	O
file	B-Application
directory	I-Application
of	O
a	O
tape	O
usually	O
requires	O
scanning	O
the	O
entire	O
tape	O
to	O
read	O
all	O
the	O
scattered	O
directory	B-Application
entries	O
.	O
</s>
<s>
Most	O
data	O
archiving	O
software	O
that	O
works	O
with	O
tape	O
storage	O
will	O
store	O
a	O
local	O
copy	O
of	O
the	O
tape	O
catalog	O
on	O
a	O
disk	B-Application
file	I-Application
system	I-Application
,	O
so	O
that	O
adding	O
files	B-Operating_System
to	O
a	O
tape	O
can	O
be	O
done	O
quickly	O
without	O
having	O
to	O
rescan	O
the	O
tape	O
media	O
.	O
</s>
<s>
The	O
local	O
tape	O
catalog	O
copy	O
is	O
usually	O
discarded	O
if	O
not	O
used	O
for	O
a	O
specified	O
period	O
of	O
time	B-Operating_System
,	O
at	O
which	O
point	O
the	O
tape	O
must	O
be	O
re-scanned	O
if	O
it	O
is	O
to	O
be	O
used	O
in	O
the	O
future	O
.	O
</s>
<s>
IBM	O
has	O
developed	O
a	O
file	B-Application
system	I-Application
for	O
tape	O
called	O
the	O
Linear	B-Device
Tape	I-Device
File	I-Device
System	I-Device
.	O
</s>
<s>
The	O
IBM	O
implementation	O
of	O
this	O
file	B-Application
system	I-Application
has	O
been	O
released	O
as	O
the	O
open-source	O
IBM	O
Linear	B-Device
Tape	I-Device
File	I-Device
System	I-Device
—	O
Single	O
Drive	O
Edition	O
(	O
LTFS-SDE	O
)	O
product	O
.	O
</s>
<s>
The	O
Linear	B-Device
Tape	I-Device
File	I-Device
System	I-Device
uses	O
a	O
separate	O
partition	B-Application
on	O
the	O
tape	O
to	O
record	O
the	O
index	O
meta-data	O
,	O
thereby	O
avoiding	O
the	O
problems	O
associated	O
with	O
scattering	O
directory	B-Application
entries	O
across	O
the	O
entire	O
tape	O
.	O
</s>
<s>
Writing	O
data	O
to	O
a	O
tape	O
,	O
erasing	O
,	O
or	O
formatting	O
a	O
tape	O
is	O
often	O
a	O
significantly	O
time-consuming	O
process	O
and	O
can	O
take	O
several	O
hours	O
on	O
large	O
tapes	O
.	O
</s>
<s>
Because	O
of	O
the	O
time	B-Operating_System
it	O
can	O
take	O
to	O
format	O
a	O
tape	O
,	O
typically	O
tapes	O
are	O
pre-formatted	O
so	O
that	O
the	O
tape	O
user	O
does	O
not	O
need	O
to	O
spend	O
time	B-Operating_System
preparing	O
each	O
new	O
tape	O
for	O
use	O
.	O
</s>
<s>
All	O
that	O
is	O
usually	O
necessary	O
is	O
to	O
write	O
an	O
identifying	O
media	O
label	O
to	O
the	O
tape	O
before	O
use	O
,	O
and	O
even	O
this	O
can	O
be	O
automatically	O
written	O
by	O
software	O
when	O
a	O
new	O
tape	O
is	O
used	O
for	O
the	O
first	O
time	B-Operating_System
.	O
</s>
<s>
Another	O
concept	O
for	O
file	B-Application
management	I-Application
is	O
the	O
idea	O
of	O
a	O
database-based	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Instead	O
of	O
,	O
or	O
in	O
addition	O
to	O
,	O
hierarchical	O
structured	O
management	O
,	O
files	B-Operating_System
are	O
identified	O
by	O
their	O
characteristics	O
,	O
like	O
type	O
of	O
file	B-Operating_System
,	O
topic	O
,	O
author	O
,	O
or	O
similar	O
rich	O
metadata	O
.	O
</s>
<s>
IBM	O
DB2	O
for	O
i	O
(	O
formerly	O
known	O
as	O
DB2/400	O
and	O
DB2	O
for	O
i5/OS	B-Application
)	O
is	O
a	O
database	O
file	B-Application
system	I-Application
as	O
part	O
of	O
the	O
object	B-Device
based	O
IBM	B-Application
i	I-Application
operating	B-General_Concept
system	I-General_Concept
(	O
formerly	O
known	O
as	O
OS/400	B-Application
and	O
i5/OS	B-Application
)	O
,	O
incorporating	O
a	O
single	B-Device
level	I-Device
store	I-Device
and	O
running	O
on	O
IBM	O
Power	O
Systems	O
(	O
formerly	O
known	O
as	O
AS/400	O
and	O
iSeries	O
)	O
,	O
designed	O
by	O
Frank	O
G	O
.	O
Soltis	O
IBM	O
's	O
former	O
chief	O
scientist	O
for	O
IBM	B-Application
i	I-Application
.	O
</s>
<s>
Around	O
1978	O
to	O
1988	O
Frank	O
G	O
.	O
Soltis	O
and	O
his	O
team	O
at	O
IBM	O
Rochester	O
have	O
successfully	O
designed	O
and	O
applied	O
technologies	O
like	O
the	O
database	O
file	B-Application
system	I-Application
where	O
others	O
like	O
Microsoft	O
later	O
failed	O
to	O
accomplish	O
.	O
</s>
<s>
Some	O
other	O
projects	O
that	O
are	O
n't	O
"	O
pure	O
"	O
database	O
file	B-Application
systems	I-Application
but	O
that	O
use	O
some	O
aspects	O
of	O
a	O
database	O
file	B-Application
system	I-Application
:	O
</s>
<s>
Many	O
Web	O
content	O
management	O
systems	O
use	O
a	O
relational	B-Application
DBMS	I-Application
to	O
store	O
and	O
retrieve	O
files	B-Operating_System
.	O
</s>
<s>
For	O
example	O
,	O
XHTML	B-Language
files	B-Operating_System
are	O
stored	B-General_Concept
as	O
XML	B-Protocol
or	O
text	O
fields	O
,	O
while	O
image	O
files	B-Operating_System
are	O
stored	B-General_Concept
as	O
blob	O
fields	O
;	O
SQL	B-Language
SELECT	O
(	O
with	O
optional	O
XPath	B-Language
)	O
statements	O
retrieve	O
the	O
files	B-Operating_System
,	O
and	O
allow	O
the	O
use	O
of	O
a	O
sophisticated	O
logic	O
and	O
more	O
rich	O
information	O
associations	O
than	O
"	O
usual	O
file	O
systems.	O
"	O
</s>
<s>
Many	O
CMSs	O
also	O
have	O
the	O
option	O
of	O
storing	O
only	O
metadata	O
within	O
the	O
database	O
,	O
with	O
the	O
standard	O
filesystem	B-Application
used	O
to	O
store	O
the	O
content	O
of	O
files	B-Operating_System
.	O
</s>
<s>
Very	O
large	O
file	B-Application
systems	I-Application
,	O
embodied	O
by	O
applications	O
like	O
Apache	B-Application
Hadoop	I-Application
and	O
Google	B-Application
File	I-Application
System	I-Application
,	O
use	O
some	O
database	O
file	B-Application
system	I-Application
concepts	O
.	O
</s>
<s>
Some	O
programs	O
need	O
to	O
either	O
make	O
multiple	O
file	B-Application
system	I-Application
changes	O
,	O
or	O
,	O
if	O
one	O
or	O
more	O
of	O
the	O
changes	O
fail	O
for	O
any	O
reason	O
,	O
make	O
none	O
of	O
the	O
changes	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
program	O
which	O
is	O
installing	O
or	O
updating	O
software	O
may	O
write	O
executables	B-Application
,	O
libraries	O
,	O
and/or	O
configuration	O
files	B-Operating_System
.	O
</s>
<s>
An	O
incomplete	O
update	O
of	O
a	O
key	O
system	O
utility	O
,	O
such	O
as	O
the	O
command	O
shell	B-Operating_System
,	O
may	O
leave	O
the	O
entire	O
system	O
in	O
an	O
unusable	O
state	O
.	O
</s>
<s>
Transaction	B-General_Concept
processing	I-General_Concept
introduces	O
the	O
atomicity	B-General_Concept
guarantee	O
,	O
ensuring	O
that	O
operations	O
inside	O
of	O
a	O
transaction	O
are	O
either	O
all	O
committed	O
or	O
the	O
transaction	O
can	O
be	O
aborted	O
and	O
the	O
system	O
discards	O
all	O
of	O
its	O
partial	O
results	O
.	O
</s>
<s>
This	O
means	O
that	O
if	O
there	O
is	O
a	O
crash	O
or	O
power	O
failure	O
,	O
after	O
recovery	O
,	O
the	O
stored	B-General_Concept
state	O
will	O
be	O
consistent	O
.	O
</s>
<s>
Transactions	O
also	O
provide	O
the	O
isolation	B-General_Concept
guarantee	O
,	O
meaning	O
that	O
operations	O
within	O
a	O
transaction	O
are	O
hidden	O
from	O
other	O
threads	O
on	O
the	O
system	O
until	O
the	O
transaction	O
commits	O
,	O
and	O
that	O
interfering	O
operations	O
on	O
the	O
system	O
will	O
be	O
properly	O
serialized	B-Application
with	O
the	O
transaction	O
.	O
</s>
<s>
Windows	B-Application
,	O
beginning	O
with	O
Vista	O
,	O
added	O
transaction	O
support	O
to	O
NTFS	B-Application
,	O
in	O
a	O
feature	O
called	O
Transactional	O
NTFS	B-Application
,	O
but	O
its	O
use	O
is	O
now	O
discouraged	O
.	O
</s>
<s>
There	O
are	O
a	O
number	O
of	O
research	O
prototypes	O
of	O
transactional	O
file	B-Application
systems	I-Application
for	O
UNIX	B-Application
systems	I-Application
,	O
including	O
the	O
Valor	O
file	B-Application
system	I-Application
,	O
Amino	O
,	O
LFS	O
,	O
and	O
a	O
transactional	O
ext3	B-Application
file	B-Application
system	I-Application
on	O
the	O
TxOS	O
kernel	O
,	O
as	O
well	O
as	O
transactional	O
file	B-Application
systems	I-Application
targeting	O
embedded	O
systems	O
,	O
such	O
as	O
TFFS	O
.	O
</s>
<s>
Ensuring	O
consistency	O
across	O
multiple	O
file	B-Application
system	I-Application
operations	O
is	O
difficult	O
,	O
if	O
not	O
impossible	O
,	O
without	O
file	B-Application
system	I-Application
transactions	O
.	O
</s>
<s>
File	B-Application
locking	I-Application
can	O
be	O
used	O
as	O
a	O
concurrency	B-Operating_System
control	I-Operating_System
mechanism	O
for	O
individual	O
files	B-Operating_System
,	O
but	O
it	O
typically	O
does	O
not	O
protect	O
the	O
directory	B-Architecture
structure	I-Architecture
or	O
file	B-Operating_System
metadata	O
.	O
</s>
<s>
For	O
instance	O
,	O
file	B-Application
locking	I-Application
cannot	O
prevent	O
TOCTTOU	B-Error_Name
race	O
conditions	O
on	O
symbolic	B-Application
links	I-Application
.	O
</s>
<s>
File	B-Application
locking	I-Application
also	O
cannot	O
automatically	O
roll	O
back	O
a	O
failed	O
operation	O
,	O
such	O
as	O
a	O
software	O
upgrade	O
;	O
this	O
requires	O
atomicity	B-General_Concept
.	O
</s>
<s>
Journaling	B-Application
file	I-Application
systems	I-Application
is	O
one	O
technique	O
used	O
to	O
introduce	O
transaction-level	O
consistency	O
to	O
file	B-Application
system	I-Application
structures	O
.	O
</s>
<s>
Journal	O
transactions	O
are	O
not	O
exposed	O
to	O
programs	O
as	O
part	O
of	O
the	O
OS	O
API	B-Application
;	O
they	O
are	O
only	O
used	O
internally	O
to	O
ensure	O
consistency	O
at	O
the	O
granularity	O
of	O
a	O
single	O
system	O
call	O
.	O
</s>
<s>
Data	O
backup	O
systems	O
typically	O
do	O
not	O
provide	O
support	O
for	O
direct	O
backup	O
of	O
data	O
stored	B-General_Concept
in	O
a	O
transactional	O
manner	O
,	O
which	O
makes	O
the	O
recovery	O
of	O
reliable	O
and	O
consistent	O
data	O
sets	O
difficult	O
.	O
</s>
<s>
Most	O
backup	O
software	O
simply	O
notes	O
what	O
files	B-Operating_System
have	O
changed	O
since	O
a	O
certain	O
time	B-Operating_System
,	O
regardless	O
of	O
the	O
transactional	O
state	O
shared	O
across	O
multiple	O
files	B-Operating_System
in	O
the	O
overall	O
dataset	O
.	O
</s>
<s>
As	O
a	O
workaround	O
,	O
some	O
database	B-Application
systems	I-Application
simply	O
produce	O
an	O
archived	O
state	O
file	B-Operating_System
containing	O
all	O
data	O
up	O
to	O
that	O
point	O
,	O
and	O
the	O
backup	O
software	O
only	O
backs	O
that	O
up	O
and	O
does	O
not	O
interact	O
directly	O
with	O
the	O
active	O
transactional	O
databases	B-Application
at	O
all	O
.	O
</s>
<s>
Recovery	O
requires	O
separate	O
recreation	O
of	O
the	O
database	O
from	O
the	O
state	O
file	B-Operating_System
after	O
the	O
file	B-Operating_System
has	O
been	O
restored	O
by	O
the	O
backup	O
software	O
.	O
</s>
<s>
A	O
network	B-Protocol
file	I-Protocol
system	I-Protocol
is	O
a	O
file	B-Application
system	I-Application
that	O
acts	O
as	O
a	O
client	O
for	O
a	O
remote	O
file	B-Application
access	I-Application
protocol	O
,	O
providing	O
access	O
to	O
files	B-Operating_System
on	O
a	O
server	O
.	O
</s>
<s>
Programs	O
using	O
local	O
interfaces	O
can	O
transparently	O
create	O
,	O
manage	O
and	O
access	O
hierarchical	O
directories	B-Application
and	O
files	B-Operating_System
in	O
remote	O
network-connected	O
computers	O
.	O
</s>
<s>
Examples	O
of	O
network	B-Application
file	I-Application
systems	I-Application
include	O
clients	O
for	O
the	O
NFS	B-Protocol
,	O
AFS	B-Application
,	O
SMB	B-Operating_System
protocols	I-Operating_System
,	O
and	O
file-system-like	O
clients	O
for	O
FTP	B-Protocol
and	O
WebDAV	B-Protocol
.	O
</s>
<s>
A	O
shared	B-General_Concept
disk	I-General_Concept
file	B-Application
system	I-Application
is	O
one	O
in	O
which	O
a	O
number	O
of	O
machines	O
(	O
usually	O
servers	O
)	O
all	O
have	O
access	O
to	O
the	O
same	O
external	O
disk	B-Device
subsystem	I-Device
(	O
usually	O
a	O
storage	O
area	O
network	O
)	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
arbitrates	O
access	O
to	O
that	O
subsystem	O
,	O
preventing	O
write	O
collisions	O
.	O
</s>
<s>
Examples	O
include	O
GFS2	B-Application
from	O
Red	O
Hat	O
,	O
GPFS	B-Application
,	O
now	O
known	O
as	O
Spectrum	B-Application
Scale	I-Application
,	O
from	O
IBM	O
,	O
SFS	B-Application
from	O
DataPlow	O
,	O
CXFS	B-Language
from	O
SGI	O
,	O
StorNext	O
from	O
Quantum	O
Corporation	O
and	O
ScoutFS	O
from	O
Versity	O
.	O
</s>
<s>
A	O
special	B-Application
file	I-Application
system	O
presents	O
non-file	O
elements	O
of	O
an	O
operating	B-General_Concept
system	I-General_Concept
as	O
files	B-Operating_System
so	O
they	O
can	O
be	O
acted	O
on	O
using	O
file	B-Application
system	I-Application
APIs	I-Application
.	O
</s>
<s>
This	O
is	O
most	O
commonly	O
done	O
in	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
but	O
devices	O
are	O
given	O
file	B-Operating_System
names	O
in	O
some	O
non-Unix-like	O
operating	O
systems	O
as	O
well	O
.	O
</s>
<s>
A	O
device	B-Application
file	I-Application
system	O
represents	O
I/O	O
devices	O
and	O
pseudo-devices	O
as	O
files	B-Operating_System
,	O
called	O
device	B-Application
files	I-Application
.	O
</s>
<s>
Examples	O
in	O
Unix-like	B-Operating_System
systems	I-Operating_System
include	O
devfs	O
and	O
,	O
in	O
Linux	B-Application
2.6	O
systems	O
,	O
udev	B-Application
.	O
</s>
<s>
In	O
non-Unix-like	O
systems	O
,	O
such	O
as	O
TOPS-10	B-Operating_System
and	O
other	O
operating	B-General_Concept
systems	I-General_Concept
influenced	O
by	O
it	O
,	O
where	O
the	O
full	O
filename	O
or	O
pathname	B-Application
of	O
a	O
file	B-Operating_System
can	O
include	O
a	O
device	O
prefix	O
,	O
devices	O
other	O
than	O
those	O
containing	O
file	B-Application
systems	I-Application
are	O
referred	O
to	O
by	O
a	O
device	O
prefix	O
specifying	O
the	O
device	O
,	O
without	O
anything	O
following	O
it	O
.	O
</s>
<s>
In	O
the	O
Linux	B-Application
kernel	O
,	O
configfs	B-Application
and	O
sysfs	B-Application
provide	O
files	B-Operating_System
that	O
can	O
be	O
used	O
to	O
query	O
the	O
kernel	O
for	O
information	O
and	O
configure	O
entities	O
in	O
the	O
kernel	O
.	O
</s>
<s>
procfs	B-Application
maps	O
processes	O
and	O
,	O
on	O
Linux	B-Application
,	O
other	O
operating	B-General_Concept
system	I-General_Concept
structures	O
into	O
a	O
filespace	O
.	O
</s>
<s>
In	O
the	O
1970s	O
disk	O
and	O
digital	O
tape	O
devices	O
were	O
too	O
expensive	O
for	O
some	O
early	O
microcomputer	B-Architecture
users	O
.	O
</s>
<s>
An	O
inexpensive	O
basic	O
data	B-General_Concept
storage	I-General_Concept
system	O
was	O
devised	O
that	O
used	O
common	O
audio	B-Device
cassette	I-Device
tape	I-Device
.	O
</s>
<s>
The	O
system	O
wrote	O
a	O
sound	O
to	O
provide	O
time	B-Operating_System
synchronization	O
,	O
then	O
modulated	B-Device
sounds	I-Device
that	O
encoded	O
a	O
prefix	O
,	O
the	O
data	O
,	O
a	O
checksum	B-Algorithm
and	O
a	O
suffix	O
.	O
</s>
<s>
Data	O
was	O
stored	B-General_Concept
sequentially	O
,	O
usually	O
in	O
an	O
unnamed	O
format	O
,	O
although	O
some	O
systems	O
(	O
such	O
as	O
the	O
Commodore	B-Device
PET	I-Device
series	O
of	O
computers	O
)	O
did	O
allow	O
the	O
files	B-Operating_System
to	O
be	O
named	O
.	O
</s>
<s>
In	O
a	O
flat	B-Application
file	I-Application
system	O
,	O
there	O
are	O
no	O
subdirectories	B-Application
;	O
directory	B-Application
entries	O
for	O
all	O
files	B-Operating_System
are	O
stored	B-General_Concept
in	O
a	O
single	O
directory	B-Application
.	O
</s>
<s>
When	O
floppy	B-Device
disk	I-Device
media	O
was	O
first	O
available	O
this	O
type	O
of	O
file	B-Application
system	I-Application
was	O
adequate	O
due	O
to	O
the	O
relatively	O
small	O
amount	O
of	O
data	O
space	O
available	O
.	O
</s>
<s>
CP/M	B-Application
machines	O
featured	O
a	O
flat	B-Application
file	I-Application
system	O
,	O
where	O
files	B-Operating_System
could	O
be	O
assigned	O
to	O
one	O
of	O
16	O
user	O
areas	O
and	O
generic	O
file	B-Operating_System
operations	O
narrowed	O
to	O
work	O
on	O
one	O
instead	O
of	O
defaulting	O
to	O
work	O
on	O
all	O
of	O
them	O
.	O
</s>
<s>
These	O
user	O
areas	O
were	O
no	O
more	O
than	O
special	O
attributes	O
associated	O
with	O
the	O
files	B-Operating_System
;	O
that	O
is	O
,	O
it	O
was	O
not	O
necessary	O
to	O
define	O
specific	O
quota	B-Application
for	O
each	O
of	O
these	O
areas	O
and	O
files	B-Operating_System
could	O
be	O
added	O
to	O
groups	O
for	O
as	O
long	O
as	O
there	O
was	O
still	O
free	O
storage	O
space	O
on	O
the	O
disk	O
.	O
</s>
<s>
The	O
early	O
Apple	B-Device
Macintosh	I-Device
also	O
featured	O
a	O
flat	B-Application
file	I-Application
system	O
,	O
the	O
Macintosh	B-Application
File	I-Application
System	I-Application
.	O
</s>
<s>
It	O
was	O
unusual	O
in	O
that	O
the	O
file	B-Application
management	I-Application
program	O
(	O
Macintosh	B-Application
Finder	I-Application
)	O
created	O
the	O
illusion	O
of	O
a	O
partially	O
hierarchical	O
filing	O
system	O
on	O
top	O
of	O
EMFS	O
.	O
</s>
<s>
This	O
structure	O
required	O
every	O
file	B-Operating_System
to	O
have	O
a	O
unique	O
name	O
,	O
even	O
if	O
it	O
appeared	O
to	O
be	O
in	O
a	O
separate	O
folder	O
.	O
</s>
<s>
IBM	O
DOS/360	O
and	O
OS/360	B-Application
store	O
entries	O
for	O
all	O
files	B-Operating_System
on	O
a	O
disk	O
pack	O
(	O
volume	O
)	O
in	O
a	O
directory	B-Application
on	O
the	O
pack	O
called	O
a	O
Volume	B-Application
Table	I-Application
of	I-Application
Contents	I-Application
(	O
VTOC	B-Application
)	O
.	O
</s>
<s>
While	O
simple	O
,	O
flat	B-Application
file	I-Application
systems	O
become	O
awkward	O
as	O
the	O
number	O
of	O
files	B-Operating_System
grows	O
and	O
makes	O
it	O
difficult	O
to	O
organize	O
data	O
into	O
related	O
groups	O
of	O
files	B-Operating_System
.	O
</s>
<s>
A	O
recent	O
addition	O
to	O
the	O
flat	B-Application
file	I-Application
system	O
family	O
is	O
Amazon	B-Application
's	O
S3	B-General_Concept
,	O
a	O
remote	O
storage	O
service	O
,	O
which	O
is	O
intentionally	O
simplistic	O
to	O
allow	O
users	O
the	O
ability	O
to	O
customize	O
how	O
their	O
data	O
is	O
stored	B-General_Concept
.	O
</s>
<s>
The	O
only	O
constructs	O
are	O
buckets	O
(	O
imagine	O
a	O
disk	O
drive	O
of	O
unlimited	O
size	O
)	O
and	O
objects	O
(	O
similar	O
,	O
but	O
not	O
identical	O
to	O
the	O
standard	O
concept	O
of	O
a	O
file	B-Operating_System
)	O
.	O
</s>
<s>
Advanced	O
file	B-Application
management	I-Application
is	O
allowed	O
by	O
being	O
able	O
to	O
use	O
nearly	O
any	O
character	O
(	O
including	O
'	O
/	O
'	O
)	O
in	O
the	O
object	B-Device
's	O
name	O
,	O
and	O
the	O
ability	O
to	O
select	O
subsets	O
of	O
the	O
bucket	O
's	O
content	O
based	O
on	O
identical	O
prefixes	O
.	O
</s>
<s>
Many	O
operating	B-General_Concept
systems	I-General_Concept
include	O
support	O
for	O
more	O
than	O
one	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Sometimes	O
the	O
OS	O
and	O
the	O
file	B-Application
system	I-Application
are	O
so	O
tightly	O
interwoven	O
that	O
it	O
is	O
difficult	O
to	O
separate	O
out	O
file	B-Application
system	I-Application
functions	O
.	O
</s>
<s>
There	O
needs	O
to	O
be	O
an	O
interface	O
provided	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
software	O
between	O
the	O
user	O
and	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
This	O
interface	O
can	O
be	O
textual	O
(	O
such	O
as	O
provided	O
by	O
a	O
command	B-Application
line	I-Application
interface	I-Application
,	O
such	O
as	O
the	O
Unix	B-Application
shell	I-Application
,	O
or	O
OpenVMS	B-Operating_System
DCL	I-Operating_System
)	O
or	O
graphical	O
(	O
such	O
as	O
provided	O
by	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
,	O
such	O
as	O
file	B-Application
browsers	I-Application
)	O
.	O
</s>
<s>
If	O
graphical	O
,	O
the	O
metaphor	O
of	O
the	O
folder	O
,	O
containing	O
documents	O
,	O
other	O
files	B-Operating_System
,	O
and	O
nested	O
folders	O
is	O
often	O
used	O
(	O
see	O
also	O
:	O
directory	B-Application
and	O
folder	O
)	O
.	O
</s>
<s>
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
create	O
a	O
virtual	B-Application
file	I-Application
system	I-Application
,	O
which	O
makes	O
all	O
the	O
files	B-Operating_System
on	O
all	O
the	O
devices	O
appear	O
to	O
exist	O
in	O
a	O
single	O
hierarchy	O
.	O
</s>
<s>
This	O
means	O
,	O
in	O
those	O
systems	O
,	O
there	O
is	O
one	O
root	B-Application
directory	I-Application
,	O
and	O
every	O
file	B-Operating_System
existing	O
on	O
the	O
system	O
is	O
located	O
under	O
it	O
somewhere	O
.	O
</s>
<s>
Unix-like	B-Operating_System
systems	I-Operating_System
can	O
use	O
a	O
RAM	B-Application
disk	I-Application
or	O
network	O
shared	B-General_Concept
resource	I-General_Concept
as	O
its	O
root	B-Application
directory	I-Application
.	O
</s>
<s>
Unix-like	B-Operating_System
systems	I-Operating_System
assign	O
a	O
device	B-Application
name	I-Application
to	O
each	O
device	O
,	O
but	O
this	O
is	O
not	O
how	O
the	O
files	B-Operating_System
on	O
that	O
device	O
are	O
accessed	O
.	O
</s>
<s>
Instead	O
,	O
to	O
gain	O
access	O
to	O
files	B-Operating_System
on	O
another	O
device	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
must	O
first	O
be	O
informed	O
where	O
in	O
the	O
directory	B-Application
tree	I-Application
those	O
files	B-Operating_System
should	O
appear	O
.	O
</s>
<s>
This	O
process	O
is	O
called	O
mounting	B-Application
a	O
file	B-Application
system	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
to	O
access	O
the	O
files	B-Operating_System
on	O
a	O
CD-ROM	B-Device
,	O
one	O
must	O
tell	O
the	O
operating	B-General_Concept
system	I-General_Concept
"	O
Take	O
the	O
file	B-Application
system	I-Application
from	O
this	O
CD-ROM	B-Device
and	O
make	O
it	O
appear	O
under	O
such-and-such	O
directory.	O
"	O
</s>
<s>
The	O
directory	B-Application
given	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
called	O
the	O
mount	O
point	O
–	O
it	O
might	O
,	O
for	O
example	O
,	O
be	O
.	O
</s>
<s>
The	O
directory	B-Application
exists	O
on	O
many	O
Unix	B-Application
systems	I-Application
(	O
as	O
specified	O
in	O
the	O
Filesystem	B-Application
Hierarchy	I-Application
Standard	I-Application
)	O
and	O
is	O
intended	O
specifically	O
for	O
use	O
as	O
a	O
mount	O
point	O
for	O
removable	B-Device
media	I-Device
such	O
as	O
CDs	O
,	O
DVDs	O
,	O
USB	O
drives	O
or	O
floppy	B-Device
disks	I-Device
.	O
</s>
<s>
It	O
may	O
be	O
empty	O
,	O
or	O
it	O
may	O
contain	O
subdirectories	B-Application
for	O
mounting	B-Application
individual	O
devices	O
.	O
</s>
<s>
Generally	O
,	O
only	O
the	O
administrator	B-Application
(	O
i.e.	O
</s>
<s>
root	B-Application
user	I-Application
)	O
may	O
authorize	O
the	O
mounting	B-Application
of	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
often	O
include	O
software	O
and	O
tools	O
that	O
assist	O
in	O
the	O
mounting	B-Application
process	O
and	O
provide	O
it	O
new	O
functionality	O
.	O
</s>
<s>
Some	O
of	O
these	O
strategies	O
have	O
been	O
coined	O
"	O
auto-mounting	O
"	O
as	O
a	O
reflection	O
of	O
their	O
purpose	O
.	O
</s>
<s>
In	O
many	O
situations	O
,	O
file	B-Application
systems	I-Application
other	O
than	O
the	O
root	B-Application
need	O
to	O
be	O
available	O
as	O
soon	O
as	O
the	O
operating	B-General_Concept
system	I-General_Concept
has	O
booted	B-Operating_System
.	O
</s>
<s>
All	O
Unix-like	B-Operating_System
systems	I-Operating_System
therefore	O
provide	O
a	O
facility	O
for	O
mounting	B-Application
file	B-Application
systems	I-Application
at	O
boot	B-Operating_System
time	I-Operating_System
.	O
</s>
<s>
System	B-Application
administrators	I-Application
define	O
these	O
file	B-Application
systems	I-Application
in	O
the	O
configuration	O
file	B-Operating_System
fstab	B-Protocol
(	O
vfstab	B-Protocol
in	O
Solaris	B-Application
)	O
,	O
which	O
also	O
indicates	O
options	O
and	O
mount	O
points	O
.	O
</s>
<s>
In	O
some	O
situations	O
,	O
there	O
is	O
no	O
need	O
to	O
mount	O
certain	O
file	B-Application
systems	I-Application
at	O
boot	B-Operating_System
time	I-Operating_System
,	O
although	O
their	O
use	O
may	O
be	O
desired	O
thereafter	O
.	O
</s>
<s>
There	O
are	O
some	O
utilities	O
for	O
Unix-like	B-Operating_System
systems	I-Operating_System
that	O
allow	O
the	O
mounting	B-Application
of	O
predefined	O
file	B-Application
systems	I-Application
upon	O
demand	O
.	O
</s>
<s>
Removable	B-Device
media	I-Device
allow	O
programs	O
and	O
data	O
to	O
be	O
transferred	O
between	O
machines	O
without	O
a	O
physical	O
connection	O
.	O
</s>
<s>
Common	O
examples	O
include	O
USB	O
flash	O
drives	O
,	O
CD-ROMs	B-Device
,	O
and	O
DVDs	O
.	O
</s>
<s>
Progressive	O
Unix-like	B-Operating_System
systems	I-Operating_System
have	O
also	O
introduced	O
a	O
concept	O
called	O
supermounting	O
;	O
see	O
,	O
for	O
example	O
,	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
floppy	B-Device
disk	I-Device
that	O
has	O
been	O
supermounted	O
can	O
be	O
physically	O
removed	O
from	O
the	O
system	O
.	O
</s>
<s>
An	O
automounter	O
will	O
automatically	O
mount	O
a	O
file	B-Application
system	I-Application
when	O
a	O
reference	O
is	O
made	O
to	O
the	O
directory	B-Application
atop	O
which	O
it	O
should	O
be	O
mounted	O
.	O
</s>
<s>
This	O
is	O
usually	O
used	O
for	O
file	B-Application
systems	I-Application
on	O
network	O
servers	O
,	O
rather	O
than	O
relying	O
on	O
events	O
such	O
as	O
the	O
insertion	O
of	O
media	O
,	O
as	O
would	O
be	O
appropriate	O
for	O
removable	B-Device
media	I-Device
.	O
</s>
<s>
Linux	B-Application
supports	O
numerous	O
file	B-Application
systems	I-Application
,	O
but	O
common	O
choices	O
for	O
the	O
system	O
disk	O
on	O
a	O
block	O
device	O
include	O
the	O
ext*	O
family	O
(	O
ext2	B-Application
,	O
ext3	B-Application
and	O
ext4	B-Application
)	O
,	O
XFS	B-Application
,	O
JFS	B-Application
,	O
and	O
btrfs	B-Operating_System
.	O
</s>
<s>
For	O
raw	O
flash	O
without	O
a	O
flash	O
translation	O
layer	O
(	O
FTL	O
)	O
or	O
Memory	B-Application
Technology	I-Application
Device	I-Application
(	O
MTD	O
)	O
,	O
there	O
are	O
UBIFS	B-Application
,	O
JFFS2	B-Application
and	O
YAFFS	B-Application
,	O
among	O
others	O
.	O
</s>
<s>
SquashFS	B-Application
is	O
a	O
common	O
compressed	O
read-only	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Solaris	B-Application
in	O
earlier	O
releases	O
defaulted	O
to	O
(	O
non-journaled	O
or	O
non-logging	O
)	O
UFS	B-Operating_System
for	O
bootable	B-Operating_System
and	O
supplementary	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
Solaris	B-Application
defaulted	O
to	O
,	O
supported	O
,	O
and	O
extended	O
UFS	B-Operating_System
.	O
</s>
<s>
Support	O
for	O
other	O
file	B-Application
systems	I-Application
and	O
significant	O
enhancements	O
were	O
added	O
over	O
time	B-Operating_System
,	O
including	O
Veritas	O
Software	O
Corp	O
.	O
(	O
journaling	B-Application
)	O
VxFS	B-Application
,	O
Sun	O
Microsystems	O
(	O
clustering	O
)	O
QFS	B-Application
,	O
Sun	O
Microsystems	O
(	O
journaling	B-Application
)	O
UFS	B-Operating_System
,	O
and	O
Sun	O
Microsystems	O
(	O
open	O
source	O
,	O
poolable	O
,	O
128	O
bit	O
compressible	O
,	O
and	O
error-correcting	O
)	O
ZFS	B-Application
.	O
</s>
<s>
Kernel	O
extensions	O
were	O
added	O
to	O
Solaris	B-Application
to	O
allow	O
for	O
bootable	B-Operating_System
Veritas	O
VxFS	B-Application
operation	O
.	O
</s>
<s>
Logging	O
or	O
journaling	B-Application
was	O
added	O
to	O
UFS	B-Operating_System
in	O
Sun	O
's	O
Solaris	B-Application
7	I-Application
.	O
</s>
<s>
Releases	O
of	O
Solaris	B-Application
10	I-Application
,	O
Solaris	B-Application
Express	I-Application
,	O
OpenSolaris	B-Operating_System
,	O
and	O
other	O
open	O
source	O
variants	O
of	O
the	O
Solaris	B-Application
operating	I-Application
system	I-Application
later	O
supported	O
bootable	B-Operating_System
ZFS	B-Application
.	O
</s>
<s>
Logical	B-Application
Volume	I-Application
Management	I-Application
allows	O
for	O
spanning	O
a	O
file	B-Application
system	I-Application
across	O
multiple	O
devices	O
for	O
the	O
purpose	O
of	O
adding	O
redundancy	O
,	O
capacity	O
,	O
and/or	O
throughput	O
.	O
</s>
<s>
Legacy	O
environments	O
in	O
Solaris	B-Application
may	O
use	O
Solaris	B-Application
Volume	I-Application
Manager	I-Application
(	O
formerly	O
known	O
as	O
Solstice	B-Application
DiskSuite	I-Application
)	O
.	O
</s>
<s>
Multiple	O
operating	B-General_Concept
systems	I-General_Concept
(	O
including	O
Solaris	B-Application
)	O
may	O
use	O
Veritas	B-Application
Volume	I-Application
Manager	I-Application
.	O
</s>
<s>
Modern	O
Solaris	B-Application
based	O
operating	B-General_Concept
systems	I-General_Concept
eclipse	O
the	O
need	O
for	O
volume	B-Application
management	I-Application
through	O
leveraging	O
virtual	O
storage	O
pools	O
in	O
ZFS	B-Application
.	O
</s>
<s>
macOS	B-Application
(	O
formerly	O
Mac	B-Device
OS	I-Device
X	I-Device
)	O
uses	O
the	O
Apple	B-Application
File	I-Application
System	I-Application
(	O
APFS	B-Application
)	O
,	O
which	O
in	O
2017	O
replaced	O
a	O
file	B-Application
system	I-Application
inherited	O
from	O
classic	B-Application
Mac	I-Application
OS	I-Application
called	O
HFS	B-Application
Plus	I-Application
(	O
HFS+	B-Application
)	O
.	O
</s>
<s>
Apple	O
also	O
uses	O
the	O
term	O
"	O
Mac	B-Application
OS	I-Application
Extended	I-Application
"	O
for	O
HFS+	B-Application
.	O
</s>
<s>
HFS	B-Application
Plus	I-Application
is	O
a	O
metadata-rich	O
and	O
case-preserving	B-Application
but	O
(	O
usually	O
)	O
case-insensitive	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Due	O
to	O
the	O
Unix	B-Application
roots	O
of	O
macOS	B-Application
,	O
Unix	B-Application
permissions	O
were	O
added	O
to	O
HFS	B-Application
Plus	I-Application
.	O
</s>
<s>
Later	O
versions	O
of	O
HFS	B-Application
Plus	I-Application
added	O
journaling	B-Application
to	O
prevent	O
corruption	O
of	O
the	O
file	B-Application
system	I-Application
structure	O
and	O
introduced	O
a	O
number	O
of	O
optimizations	O
to	O
the	O
allocation	B-General_Concept
algorithms	I-General_Concept
in	O
an	O
attempt	O
to	O
defragment	B-Application
files	B-Operating_System
automatically	O
without	O
requiring	O
an	O
external	O
defragmenter	B-Application
.	O
</s>
<s>
HFS	B-Application
Plus	I-Application
uses	O
Unicode	O
to	O
store	O
filenames	O
.	O
</s>
<s>
On	O
macOS	B-Application
,	O
the	O
filetype	O
can	O
come	O
from	O
the	O
type	O
code	O
,	O
stored	B-General_Concept
in	O
file	B-Operating_System
's	O
metadata	O
,	O
or	O
the	O
filename	O
extension	O
.	O
</s>
<s>
HFS	B-Application
Plus	I-Application
has	O
three	O
kinds	O
of	O
links	O
:	O
Unix-style	B-Operating_System
hard	B-Application
links	I-Application
,	O
Unix-style	B-Operating_System
symbolic	B-Application
links	I-Application
,	O
and	O
aliases	B-Application
.	O
</s>
<s>
Aliases	B-Application
are	O
designed	O
to	O
maintain	O
a	O
link	O
to	O
their	O
original	O
file	B-Operating_System
even	O
if	O
they	O
are	O
moved	O
or	O
renamed	O
;	O
they	O
are	O
not	O
interpreted	O
by	O
the	O
file	B-Application
system	I-Application
itself	O
,	O
but	O
by	O
the	O
File	B-Application
Manager	I-Application
code	O
in	O
userland	O
.	O
</s>
<s>
macOS	B-Application
10.13	O
High	O
Sierra	O
,	O
which	O
was	O
announced	O
on	O
June	O
5	O
,	O
2017	O
at	O
Apple	O
's	O
WWDC	O
event	O
,	O
uses	O
the	O
Apple	B-Application
File	I-Application
System	I-Application
on	O
solid-state	B-Device
drives	I-Device
.	O
</s>
<s>
macOS	B-Application
also	O
supported	O
the	O
UFS	B-Operating_System
file	B-Application
system	I-Application
,	O
derived	O
from	O
the	O
BSD	B-Operating_System
Unix	I-Operating_System
Fast	O
File	B-Application
System	I-Application
via	O
NeXTSTEP	B-Application
.	O
</s>
<s>
However	O
,	O
as	O
of	O
Mac	B-Application
OS	I-Application
X	I-Application
Leopard	I-Application
,	O
macOS	B-Application
could	O
no	O
longer	O
be	O
installed	O
on	O
a	O
UFS	B-Operating_System
volume	O
,	O
nor	O
can	O
a	O
pre-Leopard	O
system	O
installed	O
on	O
a	O
UFS	B-Operating_System
volume	O
be	O
upgraded	O
to	O
Leopard	B-Application
.	O
</s>
<s>
As	O
of	O
Mac	B-Application
OS	I-Application
X	I-Application
Lion	I-Application
UFS	B-Operating_System
support	O
was	O
completely	O
dropped	O
.	O
</s>
<s>
Newer	O
versions	O
of	O
macOS	B-Application
are	O
capable	O
of	O
reading	O
and	O
writing	O
to	O
the	O
legacy	O
FAT	B-Application
file	I-Application
systems	I-Application
(	O
16	O
and	O
32	O
)	O
common	O
on	O
Windows	B-Application
.	O
</s>
<s>
They	O
are	O
also	O
capable	O
of	O
reading	O
the	O
newer	O
NTFS	B-Application
file	I-Application
systems	I-Application
for	O
Windows	B-Application
.	O
</s>
<s>
In	O
order	O
to	O
write	O
to	O
NTFS	B-Application
file	I-Application
systems	I-Application
on	O
macOS	B-Application
versions	O
prior	O
to	O
Mac	B-Device
OS	I-Device
X	I-Device
Snow	I-Device
Leopard	I-Device
third	O
party	O
software	O
is	O
necessary	O
.	O
</s>
<s>
Mac	B-Device
OS	I-Device
X	I-Device
10.6	I-Device
(	O
Snow	B-Device
Leopard	I-Device
)	O
and	O
later	O
allow	O
writing	O
to	O
NTFS	B-Application
file	I-Application
systems	I-Application
,	O
but	O
only	O
after	O
a	O
non-trivial	O
system	O
setting	O
change	O
(	O
third	O
party	O
software	O
exists	O
that	O
automates	O
this	O
)	O
.	O
</s>
<s>
Finally	O
,	O
macOS	B-Application
supports	O
reading	O
and	O
writing	O
of	O
the	O
exFAT	B-Application
file	I-Application
system	I-Application
since	O
Mac	B-Device
OS	I-Device
X	I-Device
Snow	I-Device
Leopard	I-Device
,	O
starting	O
from	O
version	O
10.6.5	O
.	O
</s>
<s>
OS/2	B-Application
1.2	O
introduced	O
the	O
High	B-Application
Performance	I-Application
File	I-Application
System	I-Application
(	O
HPFS	B-Application
)	O
.	O
</s>
<s>
HPFS	B-Application
supports	O
mixed	O
case	O
file	B-Operating_System
names	O
in	O
different	O
code	O
pages	O
,	O
long	O
file	B-Operating_System
names	O
(	O
255	O
characters	O
)	O
,	O
more	O
efficient	O
use	O
of	O
disk	B-General_Concept
space	I-General_Concept
,	O
an	O
architecture	O
that	O
keeps	O
related	O
items	O
close	O
to	O
each	O
other	O
on	O
the	O
disk	O
volume	O
,	O
less	O
fragmentation	B-Application
of	O
data	O
,	O
extent-based	B-Application
space	O
allocation	O
,	O
a	O
B+	O
tree	O
structure	O
for	O
directories	B-Application
,	O
and	O
the	O
root	B-Application
directory	I-Application
located	O
at	O
the	O
midpoint	O
of	O
the	O
disk	O
,	O
for	O
faster	O
average	O
access	O
.	O
</s>
<s>
A	O
journaled	B-Application
filesystem	I-Application
(	O
JFS	B-Application
)	O
was	O
shipped	O
in	O
1999	O
.	O
</s>
<s>
PC-BSD	B-Application
is	O
a	O
desktop	O
version	O
of	O
FreeBSD	B-Operating_System
,	O
which	O
inherits	O
FreeBSD	B-Operating_System
's	O
ZFS	B-Application
support	O
,	O
similarly	O
to	O
FreeNAS	B-Application
.	O
</s>
<s>
The	O
new	O
graphical	O
installer	O
of	O
PC-BSD	B-Application
can	O
handle	O
/	O
(	O
root	B-Application
)	O
on	O
ZFS	B-Application
and	O
RAID-Z	O
pool	O
installs	O
and	O
disk	O
encryption	O
using	O
Geli	B-Application
right	O
from	O
the	O
start	O
in	O
an	O
easy	O
convenient	O
(	O
GUI	B-Application
)	O
way	O
.	O
</s>
<s>
The	O
current	O
PC-BSD	B-Application
9.0	O
+	O
'	O
Isotope	O
Edition	O
 '	O
has	O
ZFS	B-Application
filesystem	B-Application
version	O
5	O
and	O
ZFS	B-Application
storage	O
pool	O
version	O
28	O
.	O
</s>
<s>
Plan	O
9	O
from	O
Bell	O
Labs	O
treats	O
everything	O
as	O
a	O
file	B-Operating_System
and	O
accesses	O
all	O
objects	O
as	O
a	O
file	B-Operating_System
would	O
be	O
accessed	O
(	O
i.e.	O
,	O
there	O
is	O
no	O
ioctl	B-Operating_System
or	O
mmap	B-Operating_System
)	O
:	O
networking	O
,	O
graphics	O
,	O
debugging	O
,	O
authentication	O
,	O
capabilities	O
,	O
encryption	O
,	O
and	O
other	O
services	O
are	O
accessed	O
via	O
I/O	O
operations	O
on	O
file	B-Application
descriptors	I-Application
.	O
</s>
<s>
The	O
9P	B-Operating_System
protocol	O
removes	O
the	O
difference	O
between	O
local	O
and	O
remote	O
files	B-Operating_System
.	O
</s>
<s>
File	B-Application
systems	I-Application
in	O
Plan9	O
are	O
organized	O
with	O
the	O
help	O
of	O
private	O
,	O
per-process	O
namespaces	O
,	O
allowing	O
each	O
process	O
to	O
have	O
a	O
different	O
view	O
of	O
the	O
many	O
file	B-Application
systems	I-Application
that	O
provide	O
resources	O
in	O
a	O
distributed	O
system	O
.	O
</s>
<s>
The	O
Inferno	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
shares	O
these	O
concepts	O
with	O
Plan9	O
.	O
</s>
<s>
Windows	B-Application
makes	O
use	O
of	O
the	O
FAT	B-Application
,	O
NTFS	B-Application
,	O
exFAT	B-Application
,	O
Live	B-Device
File	I-Device
System	I-Device
and	O
ReFS	B-Application
file	B-Application
systems	I-Application
(	O
the	O
last	O
of	O
these	O
is	O
only	O
supported	O
and	O
usable	O
in	O
Windows	B-Device
Server	I-Device
2012	I-Device
,	O
Windows	B-Device
Server	I-Device
2016	I-Device
,	O
Windows	B-Application
8	I-Application
,	O
Windows	B-Device
8.1	I-Device
,	O
and	O
Windows	B-Operating_System
10	I-Operating_System
;	O
Windows	B-Application
cannot	O
boot	B-Operating_System
from	O
it	O
)	O
.	O
</s>
<s>
Windows	B-Application
uses	O
a	O
drive	O
letter	O
abstraction	O
at	O
the	O
user	O
level	O
to	O
distinguish	O
one	O
disk	O
or	O
partition	B-Application
from	O
another	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
path	B-Application
represents	O
a	O
directory	B-Application
on	O
the	O
partition	B-Application
represented	O
by	O
the	O
letter	O
C	O
.	O
Drive	O
C	O
:	O
is	O
most	O
commonly	O
used	O
for	O
the	O
primary	O
hard	B-Application
disk	I-Application
drive	I-Application
partition	I-Application
,	O
on	O
which	O
Windows	B-Application
is	O
usually	O
installed	O
and	O
from	O
which	O
it	O
boots	O
.	O
</s>
<s>
This	O
"	O
tradition	O
"	O
has	O
become	O
so	O
firmly	O
ingrained	O
that	O
bugs	O
exist	O
in	O
many	O
applications	O
which	O
make	O
assumptions	O
that	O
the	O
drive	O
that	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
installed	O
on	O
is	O
C	O
.	O
The	O
use	O
of	O
drive	O
letters	O
,	O
and	O
the	O
tradition	O
of	O
using	O
"	O
C	O
"	O
as	O
the	O
drive	O
letter	O
for	O
the	O
primary	O
hard	B-Application
disk	I-Application
drive	I-Application
partition	I-Application
,	O
can	O
be	O
traced	O
to	O
MS-DOS	B-Application
,	O
where	O
the	O
letters	O
A	O
and	O
B	O
were	O
reserved	O
for	O
up	O
to	O
two	O
floppy	B-Device
disk	I-Device
drives	I-Device
.	O
</s>
<s>
This	O
in	O
turn	O
derived	O
from	O
CP/M	B-Application
in	O
the	O
1970s	O
,	O
and	O
ultimately	O
from	O
IBM	O
's	O
CP/CMS	B-Application
of	O
1967	O
.	O
</s>
<s>
The	O
family	O
of	O
FAT	B-Application
file	I-Application
systems	I-Application
is	O
supported	O
by	O
almost	O
all	O
operating	B-General_Concept
systems	I-General_Concept
for	O
personal	O
computers	O
,	O
including	O
all	O
versions	O
of	O
Windows	B-Application
and	O
MS-DOS/PC	O
DOS	O
,	O
OS/2	B-Application
,	O
and	O
DR-DOS	B-Application
.	O
</s>
<s>
(	O
PCDOS	O
is	O
an	O
OEM	O
version	O
of	O
MS-DOS	B-Application
,	O
MS-DOS	B-Application
was	O
originally	O
based	O
on	O
SCP	O
's	O
86-DOS	B-Operating_System
.	O
</s>
<s>
DR-DOS	B-Application
was	O
based	O
on	O
Digital	O
Research	O
's	O
Concurrent	B-Operating_System
DOS	I-Operating_System
,	O
a	O
successor	O
of	O
CP/M	B-Operating_System
-86	I-Operating_System
.	O
)	O
</s>
<s>
The	O
FAT	B-Application
file	I-Application
systems	I-Application
are	O
therefore	O
well-suited	O
as	O
a	O
universal	O
exchange	O
format	O
between	O
computers	O
and	O
devices	O
of	O
most	O
any	O
type	O
and	O
age	O
.	O
</s>
<s>
The	O
FAT	B-Application
file	I-Application
system	I-Application
traces	O
its	O
roots	O
back	O
to	O
an	O
(	O
incompatible	O
)	O
8-bit	O
FAT	B-Application
precursor	O
in	O
Standalone	O
Disk	O
BASIC	O
and	O
the	O
short-lived	O
MDOS/MIDAS	O
project	O
.	O
</s>
<s>
Over	O
the	O
years	O
,	O
the	O
file	B-Application
system	I-Application
has	O
been	O
expanded	O
from	O
FAT12	B-Application
to	O
FAT16	B-Application
and	O
FAT32	B-Application
.	O
</s>
<s>
Various	O
features	O
have	O
been	O
added	O
to	O
the	O
file	B-Application
system	I-Application
including	O
subdirectories	B-Application
,	O
codepage	B-Device
support	O
,	O
extended	B-Application
attributes	I-Application
,	O
and	O
long	O
filenames	O
.	O
</s>
<s>
Third	O
parties	O
such	O
as	O
Digital	O
Research	O
have	O
incorporated	O
optional	O
support	O
for	O
deletion	O
tracking	O
,	O
and	O
volume/directory/file	O
-based	O
multi-user	O
security	O
schemes	O
to	O
support	O
file	B-Operating_System
and	O
directory	B-Application
passwords	O
and	O
permissions	O
such	O
as	O
read/write/execute/delete	O
access	O
rights	O
.	O
</s>
<s>
Most	O
of	O
these	O
extensions	O
are	O
not	O
supported	O
by	O
Windows	B-Application
.	O
</s>
<s>
The	O
FAT12	B-Application
and	O
FAT16	B-Application
file	B-Application
systems	I-Application
had	O
a	O
limit	O
on	O
the	O
number	O
of	O
entries	O
in	O
the	O
root	B-Application
directory	I-Application
of	O
the	O
file	B-Application
system	I-Application
and	O
had	O
restrictions	O
on	O
the	O
maximum	O
size	O
of	O
FAT-formatted	O
disks	O
or	O
partitions	B-Application
.	O
</s>
<s>
FAT32	B-Application
addresses	O
the	O
limitations	O
in	O
FAT12	B-Application
and	O
FAT16	B-Application
,	O
except	O
for	O
the	O
file	B-General_Concept
size	I-General_Concept
limit	O
of	O
close	O
to	O
4GB	O
,	O
but	O
it	O
remains	O
limited	O
compared	O
to	O
NTFS	B-Application
.	O
</s>
<s>
FAT12	B-Application
,	O
FAT16	B-Application
and	O
FAT32	B-Application
also	O
have	O
a	O
limit	O
of	O
eight	O
characters	O
for	O
the	O
file	B-Operating_System
name	O
,	O
and	O
three	O
characters	O
for	O
the	O
extension	O
(	O
such	O
as	O
.exe	O
)	O
.	O
</s>
<s>
VFAT	B-Application
,	O
an	O
optional	O
extension	O
to	O
FAT12	B-Application
,	O
FAT16	B-Application
and	O
FAT32	B-Application
,	O
introduced	O
in	O
Windows	B-Application
95	I-Application
and	O
Windows	B-Device
NT	I-Device
3.5	I-Device
,	O
allowed	O
long	O
file	B-Operating_System
names	O
(	O
LFN	O
)	O
to	O
be	O
stored	B-General_Concept
in	O
the	O
FAT	B-Application
file	I-Application
system	I-Application
in	O
a	O
backwards	O
compatible	O
fashion	O
.	O
</s>
<s>
NTFS	B-Application
,	O
introduced	O
with	O
the	O
Windows	B-Device
NT	I-Device
operating	B-General_Concept
system	I-General_Concept
in	O
1993	O
,	O
allowed	O
ACL-based	O
permission	O
control	O
.	O
</s>
<s>
Other	O
features	O
also	O
supported	O
by	O
NTFS	B-Application
include	O
hard	B-Application
links	I-Application
,	O
multiple	O
file	B-Operating_System
streams	O
,	O
attribute	O
indexing	O
,	O
quota	B-Application
tracking	O
,	O
sparse	B-General_Concept
files	I-General_Concept
,	O
encryption	O
,	O
compression	O
,	O
and	O
reparse	O
points	O
(	O
directories	B-Application
working	O
as	O
mount-points	O
for	O
other	O
file	B-Application
systems	I-Application
,	O
symlinks	B-Application
,	O
junctions	O
,	O
remote	O
storage	O
links	O
)	O
.	O
</s>
<s>
exFAT	B-Application
has	O
certain	O
advantages	O
over	O
NTFS	B-Application
with	O
regard	O
to	O
file	B-Application
system	I-Application
overhead	O
.	O
</s>
<s>
exFAT	B-Application
is	O
not	O
backward	O
compatible	O
with	O
FAT	B-Application
file	I-Application
systems	I-Application
such	O
as	O
FAT12	B-Application
,	O
FAT16	B-Application
or	O
FAT32	B-Application
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
is	O
supported	O
with	O
newer	O
Windows	B-Application
systems	O
,	O
such	O
as	O
Windows	B-Application
XP	O
,	O
Windows	B-Application
Server	O
2003	O
,	O
Windows	B-Application
Vista	O
,	O
Windows	B-Application
2008	O
,	O
Windows	B-Application
7	O
,	O
Windows	B-Application
8	I-Application
,	O
Windows	B-Device
8.1	I-Device
,	O
Windows	B-Operating_System
10	I-Operating_System
and	O
Windows	B-Application
11	O
.	O
</s>
<s>
exFAT	B-Application
is	O
supported	O
in	O
macOS	B-Application
starting	O
with	O
version	O
10.6.5	O
(	O
Snow	B-Device
Leopard	I-Device
)	O
.	O
</s>
<s>
Support	O
in	O
other	O
operating	B-General_Concept
systems	I-General_Concept
is	O
sparse	O
since	O
implementing	O
support	O
for	O
exFAT	B-Application
requires	O
a	O
license	O
.	O
</s>
<s>
exFAT	B-Application
is	O
the	O
only	O
file	B-Application
system	I-Application
that	O
is	O
fully	O
supported	O
on	O
both	O
macOS	B-Application
and	O
Windows	B-Application
that	O
can	O
hold	O
files	B-Operating_System
larger	O
than	O
4GB	O
.	O
</s>
<s>
Prior	O
to	O
the	O
introduction	O
of	O
VSAM	O
,	O
OS/360	B-Application
systems	O
implemented	O
a	O
hybrid	O
file	B-Application
system	I-Application
.	O
</s>
<s>
The	O
system	O
was	O
designed	O
to	O
easily	O
support	O
removable	B-Device
disk	I-Device
packs	I-Device
,	O
so	O
the	O
information	O
relating	O
to	O
all	O
files	B-Operating_System
on	O
one	O
disk	O
(	O
volume	O
in	O
IBM	O
terminology	O
)	O
is	O
stored	B-General_Concept
on	O
that	O
disk	O
in	O
a	O
flat	B-Application
system	I-Application
file	I-Application
called	O
the	O
Volume	B-Application
Table	I-Application
of	I-Application
Contents	I-Application
(	O
VTOC	B-Application
)	O
.	O
</s>
<s>
The	O
VTOC	B-Application
stores	O
all	O
metadata	O
for	O
the	O
file	B-Operating_System
.	O
</s>
<s>
Later	O
a	O
hierarchical	O
directory	B-Architecture
structure	I-Architecture
was	O
imposed	O
with	O
the	O
introduction	O
of	O
the	O
System	O
Catalog	O
,	O
which	O
can	O
optionally	O
catalog	O
files	B-Operating_System
(	O
datasets	O
)	O
on	O
resident	O
and	O
removable	O
volumes	O
.	O
</s>
<s>
Cataloged	O
and	O
non-cataloged	O
datasets	O
can	O
still	O
be	O
accessed	O
using	O
information	O
in	O
the	O
VTOC	B-Application
,	O
bypassing	O
the	O
catalog	O
,	O
if	O
the	O
required	O
volume	O
id	B-Application
is	O
provided	O
to	O
the	O
OPEN	O
request	O
.	O
</s>
<s>
Still	O
later	O
the	O
VTOC	B-Application
was	O
indexed	O
to	O
speed	O
up	O
access	O
.	O
</s>
<s>
The	O
IBM	O
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
(	O
CMS	O
)	O
component	O
of	O
VM/370	B-Application
uses	O
a	O
separate	O
flat	B-Application
file	I-Application
system	O
for	O
each	O
virtual	B-Application
disk	I-Application
(	O
minidisk	O
)	O
.	O
</s>
<s>
File	B-Operating_System
data	O
and	O
control	O
information	O
are	O
scattered	O
and	O
intermixed	O
.	O
</s>
<s>
The	O
anchor	O
is	O
a	O
record	O
called	O
the	O
Master	O
File	B-Application
Directory	I-Application
(	O
MFD	O
)	O
,	O
always	O
located	O
in	O
the	O
fourth	O
block	O
on	O
the	O
disk	O
.	O
</s>
<s>
Originally	O
CMS	O
used	O
fixed-length	O
800-byte	O
blocks	B-General_Concept
,	O
but	O
later	O
versions	O
used	O
larger	O
size	O
blocks	B-General_Concept
up	O
to	O
4K	O
.	O
</s>
<s>
Access	O
to	O
a	O
data	O
record	O
requires	O
two	O
levels	O
of	O
indirection	O
,	O
where	O
the	O
file	B-Operating_System
's	O
directory	B-Application
entry	O
(	O
called	O
a	O
File	B-Operating_System
Status	O
Table	O
(	O
FST	O
)	O
entry	O
)	O
points	O
to	O
blocks	B-General_Concept
containing	O
a	O
list	O
of	O
addresses	O
of	O
the	O
individual	O
records	O
.	O
</s>
<s>
Data	O
on	O
the	O
AS/400	O
and	O
its	O
successors	O
consists	O
of	O
system	O
objects	O
mapped	O
into	O
the	O
system	O
virtual	O
address	O
space	O
in	O
a	O
single-level	B-Device
store	I-Device
.	O
</s>
<s>
Many	O
types	O
of	O
objects	O
are	O
defined	O
including	O
the	O
directories	B-Application
and	O
files	B-Operating_System
found	O
in	O
other	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
File	B-Operating_System
objects	O
,	O
along	O
with	O
other	O
types	O
of	O
objects	O
,	O
form	O
the	O
basis	O
of	O
the	O
AS/400	O
'	O
s	O
support	O
for	O
an	O
integrated	O
relational	B-Application
database	I-Application
.	O
</s>
<s>
The	O
Prospero	O
File	B-Application
System	I-Application
is	O
a	O
file	B-Application
system	I-Application
based	O
on	O
the	O
Virtual	O
System	O
Model	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
of	O
the	O
Michigan	B-Application
Terminal	I-Application
System	I-Application
(	O
MTS	O
)	O
is	O
interesting	O
because	O
:	O
(	O
i	O
)	O
it	O
provides	O
"	O
line	O
files	B-Operating_System
"	O
where	O
record	O
lengths	O
and	O
line	O
numbers	O
are	O
associated	O
as	O
metadata	O
with	O
each	O
record	O
in	O
the	O
file	B-Operating_System
,	O
lines	O
can	O
be	O
added	O
,	O
replaced	O
,	O
updated	O
with	O
the	O
same	O
or	O
different	O
length	B-General_Concept
records	O
,	O
and	O
deleted	O
anywhere	O
in	O
the	O
file	B-Operating_System
without	O
the	O
need	O
to	O
read	O
and	O
rewrite	O
the	O
entire	O
file	B-Operating_System
;	O
(	O
ii	O
)	O
using	O
program	O
keys	O
files	B-Operating_System
may	O
be	O
shared	O
or	O
permitted	O
to	O
commands	O
and	O
programs	O
in	O
addition	O
to	O
users	O
and	O
groups	O
;	O
and	O
(	O
iii	O
)	O
there	O
is	O
a	O
comprehensive	O
file	B-Application
locking	I-Application
mechanism	O
that	O
protects	O
both	O
the	O
file	B-Operating_System
's	O
data	O
and	O
its	O
metadata	O
.	O
</s>
<s>
It	O
may	O
be	O
advantageous	O
or	O
necessary	O
to	O
have	O
files	B-Operating_System
in	O
a	O
different	O
file	B-Application
system	I-Application
than	O
they	O
currently	O
exist	O
.	O
</s>
<s>
Reasons	O
include	O
the	O
need	O
for	O
an	O
increase	O
in	O
the	O
space	O
requirements	O
beyond	O
the	O
limits	O
of	O
the	O
current	O
file	B-Application
system	I-Application
.	O
</s>
<s>
The	O
depth	O
of	O
path	B-Application
may	O
need	O
to	O
be	O
increased	O
beyond	O
the	O
restrictions	O
of	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Providing	O
access	O
to	O
another	O
operating	B-General_Concept
system	I-General_Concept
which	O
does	O
not	O
support	O
the	O
existing	O
file	B-Application
system	I-Application
is	O
another	O
reason	O
.	O
</s>
<s>
In	O
some	O
cases	O
conversion	O
can	O
be	O
done	O
in-place	O
,	O
although	O
migrating	O
the	O
file	B-Application
system	I-Application
is	O
more	O
conservative	O
,	O
as	O
it	O
involves	O
a	O
creating	O
a	O
copy	O
of	O
the	O
data	O
and	O
is	O
recommended	O
.	O
</s>
<s>
On	O
Windows	B-Application
,	O
FAT	B-Application
and	O
FAT32	B-Application
file	B-Application
systems	I-Application
can	O
be	O
converted	O
to	O
NTFS	B-Application
via	O
the	O
convert.exe	O
utility	O
,	O
but	O
not	O
the	O
reverse	O
.	O
</s>
<s>
On	O
Linux	B-Application
,	O
ext2	B-Application
can	O
be	O
converted	O
to	O
ext3	B-Application
(	O
and	O
converted	O
back	O
)	O
,	O
and	O
ext3	B-Application
can	O
be	O
converted	O
to	O
ext4	B-Application
(	O
but	O
not	O
back	O
)	O
,	O
and	O
both	O
ext3	B-Application
and	O
ext4	B-Application
can	O
be	O
converted	O
to	O
btrfs	B-Operating_System
,	O
and	O
converted	O
back	O
until	O
the	O
undo	O
information	O
is	O
deleted	O
.	O
</s>
<s>
These	O
conversions	O
are	O
possible	O
due	O
to	O
using	O
the	O
same	O
format	O
for	O
the	O
file	B-Operating_System
data	O
itself	O
,	O
and	O
relocating	O
the	O
metadata	O
into	O
empty	O
space	O
,	O
in	O
some	O
cases	O
using	O
sparse	B-General_Concept
file	I-General_Concept
support	O
.	O
</s>
<s>
The	O
best	O
case	O
is	O
if	O
there	O
is	O
unused	O
space	O
on	O
media	O
which	O
will	O
contain	O
the	O
final	O
file	B-Application
system	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
to	O
migrate	O
a	O
FAT32	B-Application
file	B-Application
system	I-Application
to	O
an	O
ext2	B-Application
file	B-Application
system	I-Application
.	O
</s>
<s>
First	O
create	O
a	O
new	O
ext2	B-Application
file	B-Application
system	I-Application
,	O
then	O
copy	O
the	O
data	O
to	O
the	O
file	B-Application
system	I-Application
,	O
then	O
delete	O
the	O
FAT32	B-Application
file	B-Application
system	I-Application
.	O
</s>
<s>
An	O
alternative	O
,	O
when	O
there	O
is	O
not	O
sufficient	O
space	O
to	O
retain	O
the	O
original	O
file	B-Application
system	I-Application
until	O
the	O
new	O
one	O
is	O
created	O
,	O
is	O
to	O
use	O
a	O
work	O
area	O
(	O
such	O
as	O
a	O
removable	B-Device
media	I-Device
)	O
.	O
</s>
<s>
In	O
hierarchical	B-Application
file	I-Application
systems	I-Application
,	O
files	B-Operating_System
are	O
accessed	O
by	O
means	O
of	O
a	O
path	B-Application
that	O
is	O
a	O
branching	O
list	O
of	O
directories	B-Application
containing	O
the	O
file	B-Operating_System
.	O
</s>
<s>
Different	O
file	B-Application
systems	I-Application
have	O
different	O
limits	O
on	O
the	O
depth	O
of	O
the	O
path	B-Application
.	O
</s>
<s>
File	B-Application
systems	I-Application
also	O
have	O
a	O
limit	O
on	O
the	O
length	B-General_Concept
of	O
an	O
individual	O
filename	O
.	O
</s>
<s>
Copying	O
files	B-Operating_System
with	O
long	O
names	O
or	O
located	O
in	O
paths	O
of	O
significant	O
depth	O
from	O
one	O
file	B-Application
system	I-Application
to	O
another	O
may	O
cause	O
undesirable	O
results	O
.	O
</s>
