<s>
A	O
computer	B-Operating_System
file	I-Operating_System
is	O
a	O
computer	B-General_Concept
resource	I-General_Concept
for	O
recording	O
data	B-General_Concept
in	O
a	O
computer	B-General_Concept
storage	I-General_Concept
device	I-General_Concept
,	O
primarily	O
identified	O
by	O
its	O
file	B-Device
name	I-Device
.	O
</s>
<s>
Just	O
as	O
words	O
can	O
be	O
written	O
to	O
paper	O
,	O
so	O
can	O
data	B-General_Concept
be	O
written	O
to	O
a	O
computer	B-Operating_System
file	I-Operating_System
.	O
</s>
<s>
Files	O
can	O
be	O
shared	O
with	O
and	O
transferred	O
between	O
computers	O
and	O
mobile	B-Application
devices	I-Application
via	O
removable	B-Device
media	I-Device
,	O
networks	B-Architecture
,	O
or	O
the	O
Internet	O
.	O
</s>
<s>
Different	O
types	O
of	O
computer	B-Operating_System
files	I-Operating_System
are	O
designed	O
for	O
different	O
purposes	O
.	O
</s>
<s>
A	O
file	O
may	O
be	O
designed	O
to	O
store	O
an	O
Image	B-Algorithm
,	O
a	O
written	O
message	O
,	O
a	O
video	O
,	O
a	O
computer	B-Application
program	I-Application
,	O
or	O
any	O
wide	O
variety	O
of	O
other	O
kinds	O
of	O
data	B-General_Concept
.	O
</s>
<s>
Certain	O
files	O
can	O
store	O
multiple	O
data	B-General_Concept
types	O
at	O
once	O
.	O
</s>
<s>
By	O
using	O
computer	B-Application
programs	I-Application
,	O
a	O
person	O
can	O
open	B-Language
,	O
read	B-Language
,	O
change	O
,	O
save	O
,	O
and	O
close	B-Language
a	O
computer	B-Operating_System
file	I-Operating_System
.	O
</s>
<s>
Computer	B-Operating_System
files	I-Operating_System
may	O
be	O
reopened	O
,	O
modified	O
,	O
and	O
copied	B-Application
an	O
arbitrary	O
number	O
of	O
times	O
.	O
</s>
<s>
Files	O
are	O
typically	O
organized	O
in	O
a	O
file	B-Application
system	I-Application
,	O
which	O
tracks	B-Device
file	O
locations	O
on	O
the	O
disk	B-Device
and	O
enables	O
user	O
access	O
.	O
</s>
<s>
"	O
File	O
"	O
was	O
used	O
in	O
the	O
context	O
of	O
computer	B-General_Concept
storage	I-General_Concept
as	O
early	O
as	O
January	O
1940	O
.	O
</s>
<s>
In	O
Punched	B-Architecture
Card	I-Architecture
Methods	O
in	O
Scientific	O
Computation	O
,	O
W	O
.	O
J	O
.	O
Eckert	O
stated	O
,	O
"	O
The	O
first	O
extensive	O
use	O
of	O
the	O
early	O
Hollerith	O
Tabulator	O
in	O
astronomy	O
was	O
made	O
by	O
Comrie	O
.	O
</s>
<s>
In	O
1952	O
,	O
"	O
file	O
"	O
denoted	O
,	O
among	O
other	O
things	O
,	O
information	O
stored	O
on	O
punched	B-Architecture
cards	I-Architecture
.	O
</s>
<s>
For	O
example	O
,	O
the	O
IBM	B-Device
350	I-Device
disk	B-Device
drives	I-Device
were	O
denominated	O
"	O
disk	B-Device
files	I-Device
"	O
.	O
</s>
<s>
The	O
introduction	O
,	O
circa	O
1961	O
,	O
by	O
the	O
Burroughs	B-Application
MCP	I-Application
and	O
the	O
MIT	O
Compatible	B-Operating_System
Time-Sharing	I-Operating_System
System	I-Operating_System
of	O
the	O
concept	O
of	O
a	O
"	O
file	B-Application
system	I-Application
"	O
that	O
managed	O
several	O
virtual	O
"	O
files	O
"	O
on	O
one	O
storage	O
device	O
is	O
the	O
origin	O
of	O
the	O
contemporary	O
denotation	O
of	O
the	O
word	O
.	O
</s>
<s>
Although	O
the	O
contemporary	O
"	O
register	B-General_Concept
file	I-General_Concept
"	O
demonstrates	O
the	O
early	O
concept	O
of	O
files	O
,	O
its	O
use	O
has	O
greatly	O
decreased	O
.	O
</s>
<s>
On	O
most	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
,	O
files	O
are	O
organized	O
into	O
one-dimensional	O
arrays	O
of	O
bytes	B-Application
.	O
</s>
<s>
The	O
format	O
of	O
a	O
file	O
is	O
defined	O
by	O
its	O
content	O
since	O
a	O
file	O
is	O
solely	O
a	O
container	O
for	O
data	B-General_Concept
.	O
</s>
<s>
On	O
some	O
platforms	O
the	O
format	O
is	O
indicated	O
by	O
its	O
filename	B-Device
extension	O
,	O
specifying	O
the	O
rules	O
for	O
how	O
the	O
bytes	B-Application
must	O
be	O
organized	O
and	O
interpreted	O
meaningfully	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
bytes	B-Application
of	O
a	O
plain	O
text	O
file	O
(	O
in	O
Windows	O
)	O
are	O
associated	O
with	O
either	O
ASCII	B-Protocol
or	O
UTF-8	O
characters	O
,	O
while	O
the	O
bytes	B-Application
of	O
image	B-Algorithm
,	O
video	O
,	O
and	O
audio	O
files	O
are	O
interpreted	O
otherwise	O
.	O
</s>
<s>
Most	O
file	O
types	O
also	O
allocate	O
a	O
few	O
bytes	B-Application
for	O
metadata	O
,	O
which	O
allows	O
a	O
file	O
to	O
carry	O
some	O
basic	O
information	O
about	O
itself	O
.	O
</s>
<s>
Some	O
file	B-Application
systems	I-Application
can	O
store	O
arbitrary	O
(	O
not	O
interpreted	O
by	O
the	O
file	B-Application
system	I-Application
)	O
file-specific	O
data	B-General_Concept
outside	O
of	O
the	O
file	O
format	O
,	O
but	O
linked	O
to	O
the	O
file	O
,	O
for	O
example	O
extended	B-Application
attributes	I-Application
or	O
forks	B-Application
.	O
</s>
<s>
On	O
other	O
file	B-Application
systems	I-Application
this	O
can	O
be	O
done	O
via	O
sidecar	O
files	O
or	O
software-specific	O
databases	O
.	O
</s>
<s>
All	O
those	O
methods	O
,	O
however	O
,	O
are	O
more	O
susceptible	O
to	O
loss	O
of	O
metadata	O
than	O
container	O
and	O
archive	B-Application
file	I-Application
formats	O
.	O
</s>
<s>
At	O
any	O
instant	O
in	O
time	O
,	O
a	O
file	O
has	O
a	O
specific	O
size	O
,	O
normally	O
expressed	O
as	O
a	O
number	O
of	O
bytes	B-Application
,	O
that	O
indicates	O
how	O
much	O
storage	O
is	O
occupied	O
by	O
the	O
file	O
.	O
</s>
<s>
In	O
most	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
the	O
size	O
can	O
be	O
any	O
non-negative	O
whole	O
number	O
of	O
bytes	B-Application
up	O
to	O
a	O
system	O
limit	O
.	O
</s>
<s>
Many	O
older	O
operating	B-General_Concept
systems	I-General_Concept
kept	O
track	O
only	O
of	O
the	O
number	O
of	O
blocks	B-Application
or	O
tracks	B-Device
occupied	O
by	O
a	O
file	O
on	O
a	O
physical	O
storage	O
device	O
.	O
</s>
<s>
In	O
such	O
systems	O
,	O
software	O
employed	O
other	O
methods	O
to	O
track	O
the	O
exact	O
byte	B-Application
count	O
(	O
e.g.	O
,	O
CP/M	B-Application
used	O
a	O
special	O
control	O
character	O
,	O
Ctrl-Z	O
,	O
to	O
signal	O
the	O
end	O
of	O
text	O
files	O
)	O
.	O
</s>
<s>
The	O
general	O
definition	O
of	O
a	O
file	O
does	O
not	O
require	O
that	O
its	O
size	O
have	O
any	O
real	O
meaning	O
,	O
however	O
,	O
unless	O
the	O
data	B-General_Concept
within	O
the	O
file	O
happens	O
to	O
correspond	O
to	O
data	B-General_Concept
within	O
a	O
pool	O
of	O
persistent	O
storage	O
.	O
</s>
<s>
A	O
special	O
case	O
is	O
a	O
zero	B-Application
byte	I-Application
file	I-Application
;	O
these	O
files	O
can	O
be	O
newly	O
created	O
files	O
that	O
have	O
not	O
yet	O
had	O
any	O
data	B-General_Concept
written	O
to	O
them	O
,	O
or	O
may	O
serve	O
as	O
some	O
kind	O
of	O
flag	O
in	O
the	O
file	B-Application
system	I-Application
,	O
or	O
are	O
accidents	O
(	O
the	O
results	O
of	O
aborted	O
disk	B-Device
operations	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
file	O
to	O
which	O
the	O
link	B-Application
points	O
in	O
a	O
typical	O
Unix-like	B-Operating_System
system	I-Operating_System
probably	O
has	O
a	O
defined	O
size	O
that	O
seldom	O
changes	O
.	O
</s>
<s>
Information	O
in	O
a	O
computer	B-Operating_System
file	I-Operating_System
can	O
consist	O
of	O
smaller	O
packets	O
of	O
information	O
(	O
often	O
called	O
"	O
records	B-Application
"	O
or	O
"	O
lines	O
"	O
)	O
that	O
are	O
individually	O
different	O
but	O
share	O
some	O
common	O
traits	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
payroll	O
file	O
might	O
contain	O
information	O
concerning	O
all	O
the	O
employees	O
in	O
a	O
company	O
and	O
their	O
payroll	O
details	O
;	O
each	O
record	O
in	O
the	O
payroll	O
file	O
concerns	O
just	O
one	O
employee	O
,	O
and	O
all	O
the	O
records	B-Application
have	O
the	O
common	O
trait	O
of	O
being	O
related	O
to	O
payroll	O
—	O
this	O
is	O
very	O
similar	O
to	O
placing	O
all	O
payroll	O
information	O
into	O
a	O
specific	O
filing	O
cabinet	O
in	O
an	O
office	O
that	O
does	O
not	O
have	O
a	O
computer	O
.	O
</s>
<s>
Alternatively	O
,	O
a	O
file	O
may	O
contain	O
an	O
arbitrary	O
binary	O
image	B-Algorithm
(	O
a	O
blob	B-General_Concept
)	O
or	O
it	O
may	O
contain	O
an	O
executable	B-Application
.	O
</s>
<s>
Most	O
computer	B-Operating_System
files	I-Operating_System
are	O
used	O
by	O
computer	B-Application
programs	I-Application
which	O
create	O
,	O
modify	O
or	O
delete	O
the	O
files	O
for	O
their	O
own	O
use	O
on	O
an	O
as-needed	O
basis	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
computer	B-Application
programs	I-Application
manipulate	O
files	O
that	O
are	O
made	O
visible	O
to	O
the	O
computer	O
user	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
a	O
word-processing	B-General_Concept
program	I-General_Concept
,	O
the	O
user	O
manipulates	O
document	O
files	O
that	O
the	O
user	O
personally	O
names	O
.	O
</s>
<s>
Although	O
the	O
content	O
of	O
the	O
document	O
file	O
is	O
arranged	O
in	O
a	O
format	O
that	O
the	O
word-processing	B-General_Concept
program	I-General_Concept
understands	O
,	O
the	O
user	O
is	O
able	O
to	O
choose	O
the	O
name	O
and	O
location	O
of	O
the	O
file	O
and	O
provide	O
the	O
bulk	O
of	O
the	O
information	O
(	O
such	O
as	O
words	O
and	O
text	O
)	O
that	O
will	O
be	O
stored	O
in	O
the	O
file	O
.	O
</s>
<s>
Many	O
applications	O
pack	O
all	O
their	O
data	B-General_Concept
files	O
into	O
a	O
single	O
file	O
called	O
an	O
archive	B-Application
file	I-Application
,	O
using	O
internal	O
markers	O
to	O
discern	O
the	O
different	O
types	O
of	O
information	O
contained	O
within	O
.	O
</s>
<s>
The	O
benefits	O
of	O
the	O
archive	B-Application
file	I-Application
are	O
to	O
lower	O
the	O
number	O
of	O
files	O
for	O
easier	O
transfer	O
,	O
to	O
reduce	O
storage	O
usage	O
,	O
or	O
just	O
to	O
organize	O
outdated	O
files	O
.	O
</s>
<s>
The	O
archive	B-Application
file	I-Application
must	O
often	O
be	O
unpacked	O
before	O
next	O
using	O
.	O
</s>
<s>
In	O
most	O
cases	O
,	O
computer	B-Application
programs	I-Application
that	O
are	O
executed	O
on	O
the	O
computer	O
handle	O
these	O
operations	O
,	O
but	O
the	O
user	O
of	O
a	O
computer	O
can	O
also	O
manipulate	O
files	O
if	O
necessary	O
.	O
</s>
<s>
For	O
instance	O
,	O
Microsoft	B-Application
Word	I-Application
files	O
are	O
normally	O
created	O
and	O
modified	O
by	O
the	O
Microsoft	B-Application
Word	I-Application
program	O
in	O
response	O
to	O
user	O
commands	O
,	O
but	O
the	O
user	O
can	O
also	O
move	O
,	O
rename	B-General_Concept
,	O
or	O
delete	O
these	O
files	O
directly	O
by	O
using	O
a	O
file	B-Application
manager	I-Application
program	I-Application
such	O
as	O
Windows	B-Protocol
Explorer	I-Protocol
(	O
on	O
Windows	B-Application
computers	I-Application
)	O
or	O
by	O
command	B-Application
lines	I-Application
(	O
CLI	O
)	O
.	O
</s>
<s>
In	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
user	B-Operating_System
space	I-Operating_System
programs	O
do	O
not	O
operate	O
directly	O
,	O
at	O
a	O
low	O
level	O
,	O
on	O
a	O
file	O
.	O
</s>
<s>
Only	O
the	O
kernel	B-Operating_System
deals	O
with	O
files	O
,	O
and	O
it	O
handles	O
all	O
user-space	B-Operating_System
interaction	O
with	O
files	O
in	O
a	O
manner	O
that	O
is	O
transparent	O
to	O
the	O
user-space	B-Operating_System
programs	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
provides	O
a	O
level	O
of	O
abstraction	B-Application
,	O
which	O
means	O
that	O
interaction	O
with	O
a	O
file	O
from	O
user-space	B-Operating_System
is	O
simply	O
through	O
its	O
filename	B-Device
(	O
instead	O
of	O
its	O
inode	B-Application
)	O
.	O
</s>
<s>
For	O
example	O
,	O
rm	B-Application
filename	B-Device
will	O
not	O
delete	O
the	O
file	O
itself	O
,	O
but	O
only	O
a	O
link	B-Application
to	O
the	O
file	O
.	O
</s>
<s>
There	O
can	O
be	O
many	O
links	O
to	O
a	O
file	O
,	O
but	O
when	O
they	O
are	O
all	O
removed	O
,	O
the	O
kernel	B-Operating_System
considers	O
that	O
file	O
's	O
memory	O
space	O
free	O
to	O
be	O
reallocated	O
.	O
</s>
<s>
This	O
free	O
space	O
is	O
commonly	O
considered	O
a	O
security	O
risk	O
(	O
due	O
to	O
the	O
existence	O
of	O
file	B-Application
recovery	I-Application
software	I-Application
)	O
.	O
</s>
<s>
Any	O
secure-deletion	O
program	O
uses	O
kernel-space	B-Operating_System
(	O
system	O
)	O
functions	O
to	O
wipe	O
the	O
file	O
's	O
data	B-General_Concept
.	O
</s>
<s>
File	O
moves	O
within	O
a	O
file	B-Application
system	I-Application
complete	O
almost	O
immediately	O
because	O
the	O
data	B-General_Concept
content	O
does	O
not	O
need	O
to	O
be	O
rewritten	O
.	O
</s>
<s>
When	O
moving	O
files	O
between	O
devices	O
or	O
partitions	O
,	O
some	O
file	O
managing	O
software	O
deletes	O
each	O
selected	O
file	O
from	O
the	O
source	O
directory	B-Application
individually	O
after	O
being	O
transferred	O
,	O
while	O
other	O
software	O
deletes	O
all	O
files	O
at	O
once	O
only	O
after	O
every	O
file	O
has	O
been	O
transferred	O
.	O
</s>
<s>
With	O
the	O
mv	O
command	O
for	O
instance	O
,	O
the	O
former	O
method	O
is	O
used	O
when	O
selecting	O
files	O
individually	O
,	O
possibly	O
with	O
the	O
use	O
of	O
wildcards	B-Algorithm
(	O
example	O
:	O
mv	O
-n	O
sourcePath/	O
*	O
targetPath	O
,	O
while	O
the	O
latter	O
method	O
is	O
used	O
when	O
selecting	O
entire	O
directories	B-Application
(	O
example	O
:	O
mv	O
-n	O
sourcePath	O
targetPath	O
)	O
.	O
</s>
<s>
Microsoft	B-Application
Windows	I-Application
Explorer	O
uses	O
the	O
former	O
method	O
for	O
mass	B-Device
storage	I-Device
filemoves	O
,	O
but	O
the	O
latter	O
method	O
using	O
Media	B-Protocol
Transfer	I-Protocol
Protocol	I-Protocol
,	O
as	O
described	O
in	O
.	O
</s>
<s>
If	O
an	O
incomplete	O
file	O
transfer	O
with	O
the	O
latter	O
method	O
is	O
aborted	O
unexpectedly	O
,	O
perhaps	O
due	O
to	O
an	O
unexpected	O
power-off	B-Device
,	O
system	O
halt	O
or	O
disconnection	O
of	O
a	O
device	O
,	O
no	O
space	O
will	O
have	O
been	O
freed	O
up	O
on	O
the	O
source	O
device	O
or	O
partition	O
.	O
</s>
<s>
A	O
file	B-Application
manager	I-Application
using	O
the	O
latter	O
(	O
afterwards	O
deletion	O
)	O
method	O
will	O
have	O
to	O
only	O
delete	O
the	O
files	O
from	O
the	O
source	O
directory	B-Application
that	O
have	O
already	O
finished	O
transferring	O
.	O
</s>
<s>
In	O
modern	O
computer	O
systems	O
,	O
files	O
are	O
typically	O
accessed	O
using	O
names	O
(	O
filenames	B-Device
)	O
.	O
</s>
<s>
In	O
some	O
operating	B-General_Concept
systems	I-General_Concept
,	O
the	O
name	O
is	O
associated	O
with	O
the	O
file	O
itself	O
.	O
</s>
<s>
In	O
the	O
latter	O
case	O
,	O
a	O
user	O
can	O
identify	O
the	O
name	O
of	O
the	O
link	B-Application
with	O
the	O
file	O
itself	O
,	O
but	O
this	O
is	O
a	O
false	O
analogue	O
,	O
especially	O
where	O
there	O
exists	O
more	O
than	O
one	O
link	B-Application
to	O
the	O
same	O
file	O
.	O
</s>
<s>
Files	O
(	O
or	O
links	O
to	O
files	O
)	O
can	O
be	O
located	O
in	O
directories	B-Application
.	O
</s>
<s>
However	O
,	O
more	O
generally	O
,	O
a	O
directory	B-Application
can	O
contain	O
either	O
a	O
list	O
of	O
files	O
or	O
a	O
list	O
of	O
links	O
to	O
files	O
.	O
</s>
<s>
Within	O
this	O
definition	O
,	O
it	O
is	O
of	O
paramount	O
importance	O
that	O
the	O
term	O
"	O
file	O
"	O
includes	O
directories	B-Application
.	O
</s>
<s>
This	O
permits	O
the	O
existence	O
of	O
directory	B-Application
hierarchies	O
,	O
i.e.	O
,	O
directories	B-Application
containing	O
sub-directories	O
.	O
</s>
<s>
A	O
name	O
that	O
refers	O
to	O
a	O
file	O
within	O
a	O
directory	B-Application
must	O
be	O
typically	O
unique	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
there	O
must	O
be	O
no	O
identical	O
names	O
within	O
a	O
directory	B-Application
.	O
</s>
<s>
However	O
,	O
in	O
some	O
operating	B-General_Concept
systems	I-General_Concept
,	O
a	O
name	O
may	O
include	O
a	O
specification	O
of	O
type	O
that	O
means	O
a	O
directory	B-Application
can	O
contain	O
an	O
identical	O
name	O
for	O
more	O
than	O
one	O
type	O
of	O
object	O
such	O
as	O
a	O
directory	B-Application
and	O
a	O
file	O
.	O
</s>
<s>
In	O
environments	O
in	O
which	O
a	O
file	O
is	O
named	O
,	O
a	O
file	O
's	O
name	O
and	O
the	O
path	O
to	O
the	O
file	O
's	O
directory	B-Application
must	O
uniquely	O
identify	O
it	O
among	O
all	O
other	O
files	O
in	O
the	O
computer	O
system	O
—	O
no	O
two	O
files	O
can	O
have	O
the	O
same	O
name	O
and	O
path	O
.	O
</s>
<s>
Any	O
string	O
of	O
characters	O
may	O
be	O
a	O
well-formed	O
name	O
for	O
a	O
file	O
or	O
a	O
link	B-Application
depending	O
upon	O
the	O
context	O
of	O
application	O
.	O
</s>
<s>
Case-sensitivity	O
of	O
file	O
names	O
is	O
determined	O
by	O
the	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Unix	O
file	B-Application
systems	I-Application
are	O
usually	O
case	O
sensitive	O
and	O
allow	O
user-level	B-Operating_System
applications	O
to	O
create	O
files	O
whose	O
names	O
differ	O
only	O
in	O
the	O
case	O
of	O
characters	O
.	O
</s>
<s>
Microsoft	B-Application
Windows	I-Application
supports	O
multiple	O
file	B-Application
systems	I-Application
,	O
each	O
with	O
different	O
policies	O
regarding	O
case-sensitivity	O
.	O
</s>
<s>
The	O
common	O
FAT	B-Application
file	I-Application
system	I-Application
can	O
have	O
multiple	O
files	O
whose	O
names	O
differ	O
only	O
in	O
case	O
if	O
the	O
user	O
uses	O
a	O
disk	B-Application
editor	I-Application
to	O
edit	O
the	O
file	O
names	O
in	O
the	O
directory	B-Application
entries	O
.	O
</s>
<s>
Most	O
computers	O
organize	O
files	O
into	O
hierarchies	O
using	O
folders	O
,	O
directories	B-Application
,	O
or	O
catalogs	O
.	O
</s>
<s>
These	O
other	O
folders	O
are	O
referred	O
to	O
as	O
subfolders	B-Application
.	O
</s>
<s>
Subfolders	B-Application
can	O
contain	O
still	O
more	O
files	O
and	O
folders	O
and	O
so	O
on	O
,	O
thus	O
building	O
a	O
tree-like	O
structure	O
in	O
which	O
one	O
"	O
master	O
folder	O
"	O
(	O
or	O
"	O
root	O
folder	O
"	O
—	O
the	O
name	O
varies	O
from	O
one	O
operating	B-General_Concept
system	I-General_Concept
to	O
another	O
)	O
can	O
contain	O
any	O
number	O
of	O
levels	O
of	O
other	O
folders	O
and	O
files	O
.	O
</s>
<s>
In	O
the	O
path	O
,	O
some	O
sort	O
of	O
special	O
character	O
—	O
such	O
as	O
a	O
slash	O
—	O
is	O
used	O
to	O
separate	O
the	O
file	O
and	O
folder	B-Application
names	I-Application
.	O
</s>
<s>
On	O
Windows	B-Application
computers	I-Application
,	O
extensions	O
consist	O
of	O
a	O
dot	O
(	O
period	O
)	O
at	O
the	O
end	O
of	O
a	O
file	B-Device
name	I-Device
,	O
followed	O
by	O
a	O
few	O
letters	O
to	O
identify	O
the	O
type	O
of	O
file	O
.	O
</s>
<s>
An	O
extension	O
of	O
identifies	O
a	O
text	O
file	O
;	O
a	O
extension	O
identifies	O
any	O
type	O
of	O
document	O
or	O
documentation	O
,	O
commonly	O
in	O
the	O
Microsoft	B-Application
Word	I-Application
file	O
format	O
;	O
and	O
so	O
on	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
given	O
user	O
may	O
be	O
granted	O
only	O
permission	O
to	O
read	B-Language
a	O
file	O
or	O
folder	O
,	O
but	O
not	O
to	O
modify	O
or	O
delete	O
it	O
;	O
or	O
a	O
user	O
may	O
be	O
given	O
permission	O
to	O
read	B-Language
and	O
modify	O
files	O
or	O
folders	O
,	O
but	O
not	O
to	O
execute	O
them	O
.	O
</s>
<s>
Another	O
protection	O
mechanism	O
implemented	O
in	O
many	O
computers	O
is	O
a	O
read-only	O
flag	O
.	O
</s>
<s>
When	O
this	O
flag	O
is	O
turned	O
on	O
for	O
a	O
file	O
(	O
which	O
can	O
be	O
accomplished	O
by	O
a	O
computer	B-Application
program	I-Application
or	O
by	O
a	O
human	O
user	O
)	O
,	O
the	O
file	O
can	O
be	O
examined	O
,	O
but	O
it	O
cannot	O
be	O
modified	O
.	O
</s>
<s>
Some	O
systems	O
also	O
include	O
a	O
hidden	B-Application
flag	I-Application
to	O
make	O
certain	O
files	O
invisible	O
;	O
this	O
flag	O
is	O
used	O
by	O
the	O
computer	O
system	O
to	O
hide	O
essential	O
system	O
files	O
that	O
users	O
should	O
not	O
alter	O
.	O
</s>
<s>
In	O
physical	O
terms	O
,	O
most	O
computer	B-Operating_System
files	I-Operating_System
are	O
stored	O
on	O
some	O
type	O
of	O
data	B-General_Concept
storage	O
device	O
.	O
</s>
<s>
For	O
example	O
,	O
most	O
operating	B-General_Concept
systems	I-General_Concept
store	O
files	O
on	O
a	O
hard	B-Device
disk	I-Device
.	O
</s>
<s>
Hard	B-Device
disks	I-Device
have	O
been	O
the	O
ubiquitous	O
form	O
of	O
non-volatile	B-General_Concept
storage	I-General_Concept
since	O
the	O
early	O
1960s	O
.	O
</s>
<s>
Where	O
files	O
contain	O
only	O
temporary	O
information	O
,	O
they	O
may	O
be	O
stored	O
in	O
RAM	B-Architecture
.	O
</s>
<s>
Computer	B-Operating_System
files	I-Operating_System
can	O
be	O
also	O
stored	O
on	O
other	O
media	O
in	O
some	O
cases	O
,	O
such	O
as	O
magnetic	O
tapes	O
,	O
compact	O
discs	O
,	O
Digital	O
Versatile	O
Discs	O
,	O
Zip	B-Operating_System
drives	I-Operating_System
,	O
USB	O
flash	B-Device
drives	I-Device
,	O
etc	O
.	O
</s>
<s>
The	O
use	O
of	O
solid	B-Device
state	I-Device
drives	I-Device
is	O
also	O
beginning	O
to	O
rival	O
the	O
hard	B-Device
disk	I-Device
drive	I-Device
.	O
</s>
<s>
In	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
many	O
files	O
have	O
no	O
associated	O
physical	O
storage	O
device	O
.	O
</s>
<s>
Examples	O
are	O
and	O
most	O
files	O
under	O
directories	B-Application
,	O
and	O
.	O
</s>
<s>
These	O
are	O
virtual	O
files	O
:	O
they	O
exist	O
as	O
objects	O
within	O
the	O
operating	B-Operating_System
system	I-Operating_System
kernel	I-Operating_System
.	O
</s>
<s>
As	O
seen	O
by	O
a	O
running	O
user	O
program	O
,	O
files	O
are	O
usually	O
represented	O
either	O
by	O
a	O
file	B-Operating_System
control	I-Operating_System
block	I-Operating_System
or	O
by	O
a	O
file	B-Application
handle	I-Application
.	O
</s>
<s>
A	O
file	B-Operating_System
control	I-Operating_System
block	I-Operating_System
(	O
FCB	O
)	O
is	O
an	O
area	O
of	O
memory	O
which	O
is	O
manipulated	O
to	O
establish	O
a	O
filename	B-Device
etc	O
.	O
</s>
<s>
and	O
then	O
passed	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
as	O
a	O
parameter	O
;	O
it	O
was	O
used	O
by	O
older	O
IBM	O
operating	B-General_Concept
systems	I-General_Concept
and	O
early	O
PC	O
operating	B-General_Concept
systems	I-General_Concept
including	O
CP/M	B-Application
and	O
early	O
versions	O
of	O
MS-DOS	B-Application
.	O
</s>
<s>
A	O
file	B-Application
handle	I-Application
is	O
generally	O
either	O
an	O
opaque	B-General_Concept
data	I-General_Concept
type	I-General_Concept
or	O
an	O
integer	O
;	O
it	O
was	O
introduced	O
in	O
around	O
1961	O
by	O
the	O
ALGOL-based	B-Language
Burroughs	B-Application
MCP	I-Application
running	O
on	O
the	O
Burroughs	B-Device
B5000	I-Device
but	O
is	O
now	O
ubiquitous	O
.	O
</s>
<s>
When	O
a	O
file	O
is	O
said	O
to	O
be	O
corrupted	O
,	O
it	O
is	O
because	O
its	O
contents	O
have	O
been	O
saved	O
to	O
the	O
computer	O
in	O
such	O
a	O
way	O
that	O
they	O
cannot	O
be	O
properly	O
read	B-Language
,	O
either	O
by	O
a	O
human	O
or	O
by	O
software	O
.	O
</s>
<s>
Depending	O
on	O
the	O
extent	O
of	O
the	O
damage	O
,	O
the	O
original	O
file	O
can	O
sometimes	O
be	O
recovered	B-Application
,	O
or	O
at	O
least	O
partially	O
understood	O
.	O
</s>
<s>
Most	O
commonly	O
,	O
the	O
issue	O
happens	O
in	O
the	O
process	O
of	O
writing	B-Language
the	O
file	O
to	O
a	O
disk	B-Device
.	O
</s>
<s>
For	O
example	O
,	O
if	O
an	O
image-editing	B-Application
program	I-Application
unexpectedly	O
crashes	B-General_Concept
while	O
saving	O
an	O
image	B-Algorithm
,	O
that	O
file	O
may	O
be	O
corrupted	O
because	O
the	O
program	O
could	O
not	O
save	O
its	O
entirety	O
.	O
</s>
<s>
The	O
computer	O
itself	O
shutting	B-Device
down	I-Device
unexpectedly	O
(	O
for	O
example	O
,	O
due	O
to	O
a	O
power	O
loss	O
)	O
with	O
open	B-Language
files	O
,	O
or	O
files	O
in	O
the	O
process	O
of	O
being	O
saved	O
;	O
</s>
<s>
A	O
download	B-Application
being	O
interrupted	O
before	O
it	O
was	O
completed	O
;	O
</s>
<s>
Due	O
to	O
a	O
bad	B-Device
sector	I-Device
on	O
the	O
hard	B-Device
drive	I-Device
;	O
</s>
<s>
The	O
user	O
removing	O
a	O
flash	B-Device
drive	I-Device
(	O
such	O
as	O
a	O
USB	O
stick	O
)	O
without	O
properly	O
unmounting	B-Application
(	O
commonly	O
referred	O
to	O
as	O
"	O
safely	O
removing	O
"	O
)	O
;	O
</s>
<s>
A	O
flash	B-Device
drive	I-Device
becoming	O
too	O
old	O
.	O
</s>
<s>
There	O
are	O
services	O
that	O
provide	O
on	O
demand	O
file	O
corruption	O
,	O
which	O
essentially	O
fill	O
a	O
given	O
file	O
with	O
random	O
data	B-General_Concept
so	O
that	O
it	O
cannot	O
be	O
opened	O
or	O
read	B-Language
,	O
yet	O
still	O
seems	O
legitimate	O
.	O
</s>
<s>
One	O
of	O
the	O
most	O
effective	O
countermeasures	O
for	O
unintentional	O
file	O
corruption	O
is	O
backing	B-Protocol
up	I-Protocol
important	O
files	O
.	O
</s>
<s>
When	O
computer	B-Operating_System
files	I-Operating_System
contain	O
information	O
that	O
is	O
extremely	O
important	O
,	O
a	O
back-up	B-Protocol
process	O
is	O
used	O
to	O
protect	O
against	O
disasters	O
that	O
might	O
destroy	O
the	O
files	O
.	O
</s>
<s>
Backing	B-Protocol
up	I-Protocol
files	O
simply	O
means	O
making	O
copies	O
of	O
the	O
files	O
in	O
a	O
separate	O
location	O
so	O
that	O
they	O
can	O
be	O
restored	O
if	O
something	O
happens	O
to	O
the	O
computer	O
,	O
or	O
if	O
they	O
are	O
deleted	O
accidentally	O
.	O
</s>
<s>
There	O
are	O
many	O
ways	O
to	O
back	B-Protocol
up	I-Protocol
files	O
.	O
</s>
<s>
Most	O
computer	O
systems	O
provide	O
utility	O
programs	O
to	O
assist	O
in	O
the	O
back-up	B-Protocol
process	O
,	O
which	O
can	O
become	O
very	O
time-consuming	O
if	O
there	O
are	O
many	O
files	O
to	O
safeguard	O
.	O
</s>
<s>
Files	O
are	O
often	O
copied	B-Application
to	O
removable	B-Device
media	I-Device
such	O
as	O
writable	O
CDs	O
or	O
cartridge	O
tapes	O
.	O
</s>
<s>
Copying	B-Application
files	I-Application
to	O
another	O
hard	B-Device
disk	I-Device
in	O
the	O
same	O
computer	O
protects	O
against	O
failure	O
of	O
one	O
disk	B-Device
,	O
but	O
if	O
it	O
is	O
necessary	O
to	O
protect	O
against	O
failure	O
or	O
destruction	O
of	O
the	O
entire	O
computer	O
,	O
then	O
copies	O
of	O
the	O
files	O
must	O
be	O
made	O
on	O
other	O
media	O
that	O
can	O
be	O
taken	O
away	O
from	O
the	O
computer	O
and	O
stored	O
in	O
a	O
safe	O
,	O
distant	O
location	O
.	O
</s>
<s>
The	O
grandfather-father-son	O
backup	B-Protocol
method	O
automatically	O
makes	O
three	O
back-ups	B-Protocol
;	O
the	O
grandfather	O
file	O
is	O
the	O
oldest	O
copy	O
of	O
the	O
file	O
and	O
the	O
son	O
is	O
the	O
current	O
copy	O
.	O
</s>
<s>
The	O
way	O
a	O
computer	O
organizes	O
,	O
names	O
,	O
stores	O
and	O
manipulates	O
files	O
is	O
globally	O
referred	O
to	O
as	O
its	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Most	O
computers	O
have	O
at	O
least	O
one	O
file	B-Application
system	I-Application
.	O
</s>
<s>
Some	O
computers	O
allow	O
the	O
use	O
of	O
several	O
different	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
For	O
instance	O
,	O
on	O
newer	O
MS	B-Application
Windows	I-Application
computers	O
,	O
the	O
older	O
FAT-type	O
file	B-Application
systems	I-Application
of	O
MS-DOS	B-Application
and	O
old	O
versions	O
of	O
Windows	O
are	O
supported	O
,	O
in	O
addition	O
to	O
the	O
NTFS	B-Application
file	I-Application
system	I-Application
that	O
is	O
the	O
normal	O
file	B-Application
system	I-Application
for	O
recent	O
versions	O
of	O
Windows	O
.	O
</s>
<s>
Standard	O
FAT	B-Application
allows	O
only	O
eight-character	O
file	O
names	O
(	O
plus	O
a	O
three-character	O
extension	O
)	O
with	O
no	O
spaces	O
,	O
for	O
example	O
,	O
whereas	O
NTFS	B-Application
allows	O
much	O
longer	O
names	O
that	O
can	O
contain	O
spaces	O
.	O
</s>
<s>
You	O
can	O
call	O
a	O
file	O
""	O
in	O
NTFS	B-Application
,	O
but	O
in	O
FAT	B-Application
you	O
would	O
be	O
restricted	O
to	O
something	O
like	O
(	O
unless	O
you	O
were	O
using	O
VFAT	O
,	O
a	O
FAT	B-Application
extension	O
allowing	O
long	O
file	O
names	O
)	O
.	O
</s>
<s>
File	B-Application
manager	I-Application
programs	O
are	O
utility	O
programs	O
that	O
allow	O
users	O
to	O
manipulate	O
files	O
directly	O
.	O
</s>
<s>
They	O
allow	O
you	O
to	O
move	O
,	O
create	O
,	O
delete	O
and	O
rename	B-General_Concept
files	O
and	O
folders	O
,	O
although	O
they	O
do	O
not	O
actually	O
allow	O
you	O
to	O
read	B-Language
the	O
contents	O
of	O
a	O
file	O
or	O
store	O
information	O
in	O
it	O
.	O
</s>
<s>
Every	O
computer	O
system	O
provides	O
at	O
least	O
one	O
file-manager	O
program	O
for	O
its	O
native	O
file	B-Application
system	I-Application
.	O
</s>
<s>
For	O
example	O
,	O
File	B-Protocol
Explorer	I-Protocol
(	O
formerly	O
Windows	B-Protocol
Explorer	I-Protocol
)	O
is	O
commonly	O
used	O
in	O
Microsoft	B-Application
Windows	I-Application
operating	I-Application
systems	I-Application
,	O
and	O
Nautilus	O
is	O
common	O
under	O
several	O
distributions	O
of	O
Linux	O
.	O
</s>
