<s>
In	O
a	O
computer	B-Application
file	I-Application
system	I-Application
,	O
a	O
fork	B-Application
is	O
a	O
set	O
of	O
data	O
associated	O
with	O
a	O
file-system	B-Application
object	O
.	O
</s>
<s>
File	B-Application
systems	I-Application
without	O
forks	B-Application
only	O
allow	O
a	O
single	O
set	O
of	O
data	O
for	O
the	O
contents	O
,	O
while	O
file	B-Application
systems	I-Application
with	O
forks	B-Application
allow	O
multiple	O
such	O
contents	O
.	O
</s>
<s>
Every	O
non-empty	O
file	O
must	O
have	O
at	O
least	O
one	O
fork	B-Application
,	O
often	O
of	O
default	O
type	O
,	O
and	O
depending	O
on	O
the	O
file	B-Application
system	I-Application
,	O
a	O
file	O
may	O
have	O
one	O
or	O
more	O
other	O
associated	O
forks	B-Application
,	O
which	O
in	O
turn	O
may	O
contain	O
primary	O
data	O
integral	O
to	O
the	O
file	O
,	O
or	O
just	O
metadata	O
.	O
</s>
<s>
Unlike	O
extended	B-Application
attributes	I-Application
,	O
a	O
similar	O
file	B-Application
system	I-Application
feature	O
which	O
is	O
typically	O
of	O
fixed	O
size	O
,	O
forks	B-Application
can	O
be	O
of	O
variable	O
size	O
,	O
possibly	O
even	O
larger	O
than	O
the	O
file	O
's	O
primary	O
data	B-Operating_System
fork	I-Operating_System
.	O
</s>
<s>
The	O
size	O
of	O
a	O
file	O
is	O
the	O
sum	O
of	O
the	O
sizes	O
of	O
each	O
fork	B-Application
.	O
</s>
<s>
On	O
file	B-Application
systems	I-Application
without	O
forks	B-Application
,	O
one	O
may	O
instead	O
use	O
multiple	O
separate	O
files	O
that	O
are	O
associated	O
with	O
each	O
other	O
,	O
particularly	O
sidecar	O
files	O
for	O
metadata	O
.	O
</s>
<s>
However	O
,	O
the	O
connection	O
between	O
these	O
files	O
is	O
not	O
automatically	O
preserved	O
by	O
the	O
file	B-Application
system	I-Application
,	O
and	O
must	O
instead	O
be	O
handled	O
by	O
each	O
program	O
that	O
works	O
on	O
files	O
.	O
</s>
<s>
Another	O
alternative	O
is	O
a	O
container	O
file	O
,	O
which	O
stores	O
additional	O
data	O
within	O
a	O
given	O
file	O
format	O
,	O
or	O
an	O
archive	B-Application
file	I-Application
,	O
which	O
allows	O
storing	O
several	O
files	O
and	O
metadata	O
within	O
a	O
file	O
(	O
within	O
a	O
single	O
fork	B-Application
)	O
.	O
</s>
<s>
This	O
requires	O
that	O
programs	O
process	O
the	O
container	O
file	O
or	O
archive	B-Application
file	I-Application
,	O
rather	O
than	O
the	O
file	B-Application
system	I-Application
handling	O
forks	B-Application
.	O
</s>
<s>
These	O
alternatives	O
require	O
additional	O
work	O
by	O
programs	O
using	O
the	O
data	O
,	O
but	O
benefit	O
from	O
portability	O
to	O
file	B-Application
systems	I-Application
that	O
do	O
not	O
support	O
forks	B-Application
.	O
</s>
<s>
File	B-Application
system	I-Application
forks	B-Application
are	O
associated	O
with	O
Apple	O
's	O
Hierarchical	B-Application
File	I-Application
System	I-Application
(	O
HFS	B-Application
)	O
.	O
</s>
<s>
HFS	B-Application
,	O
and	O
the	O
original	O
Apple	B-Device
Macintosh	I-Device
file	B-Application
system	I-Application
MFS	B-Application
,	O
allowed	O
a	O
file	B-Application
system	I-Application
object	O
to	O
have	O
two	O
kinds	O
of	O
forks	B-Application
:	O
a	O
data	B-Operating_System
fork	I-Operating_System
and	O
a	O
resource	B-Operating_System
fork	I-Operating_System
.	O
</s>
<s>
The	O
resource	B-Operating_System
fork	I-Operating_System
was	O
designed	O
to	O
store	O
non-compiled	O
data	O
that	O
would	O
be	O
used	O
by	O
the	O
system	O
's	O
graphical	B-Application
user	I-Application
interface	I-Application
(	O
GUI	B-Application
)	O
,	O
such	O
as	O
localizable	O
text	O
strings	O
,	O
a	O
file	O
's	O
icon	O
to	O
be	O
used	O
by	O
the	O
Finder	O
or	O
the	O
menus	O
and	O
dialog	O
boxes	O
associated	O
with	O
an	O
application	O
.	O
</s>
<s>
As	O
compiled	O
software	O
code	O
was	O
also	O
stored	O
in	O
a	O
resource	O
,	O
often	O
applications	O
would	O
consist	O
of	O
just	O
a	O
resource	B-Operating_System
fork	I-Operating_System
and	O
no	O
data	B-Operating_System
fork	I-Operating_System
.	O
</s>
<s>
One	O
of	O
HFS+'s	O
most	O
obscure	O
features	O
is	O
that	O
a	O
file	O
may	O
have	O
an	O
arbitrary	O
number	O
of	O
custom	O
"	O
named	O
forks	B-Application
"	O
in	O
addition	O
to	O
the	O
traditional	O
data	O
and	O
resource	B-Operating_System
forks	I-Operating_System
.	O
</s>
<s>
This	O
feature	O
has	O
gone	O
largely	O
unused	O
,	O
as	O
Apple	O
never	O
added	O
support	O
for	O
it	O
under	O
Mac	B-Device
OS	O
8.1-10.3.9	O
.	O
</s>
<s>
Beginning	O
with	O
10.4	B-Application
,	O
a	O
partial	O
implementation	O
was	O
made	O
to	O
support	O
Apple	O
's	O
extended	B-Application
inline	I-Application
attributes	I-Application
.	O
</s>
<s>
Until	O
Mac	B-Application
OS	I-Application
X	I-Application
v10.4	I-Application
,	O
users	O
running	O
the	O
Unix	B-Application
command	O
line	O
utilities	O
(	O
such	O
as	O
tar	B-Application
)	O
included	O
with	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
would	O
risk	O
data	O
loss	O
,	O
as	O
the	O
utilities	O
were	O
not	O
updated	O
to	O
handle	O
the	O
resource	B-Operating_System
forks	I-Operating_System
of	O
files	O
.	O
</s>
<s>
Starting	O
in	O
1985	O
,	O
Novell	B-Application
NetWare	I-Application
File	I-Application
System	I-Application
(	O
NWFS	B-Application
)	O
,	O
and	O
its	O
successor	O
Novell	B-Application
Storage	I-Application
Services	I-Application
(	O
NSS	B-Application
)	O
,	O
were	O
designed	O
from	O
the	O
ground	O
up	O
to	O
use	O
a	O
variety	O
of	O
methods	O
to	O
store	O
a	O
file	O
's	O
metadata	O
.	O
</s>
<s>
Some	O
metadata	O
resides	O
in	O
Novell	B-Application
Directory	I-Application
Services	I-Application
(	O
NDS	B-Application
)	O
,	O
some	O
is	O
stored	O
in	O
the	O
directory	O
structure	O
on	O
the	O
disk	O
,	O
and	O
some	O
is	O
stored	O
in	O
,	O
as	O
Novell	O
terms	O
it	O
,	O
'	O
multiple	O
data	O
streams	O
 '	O
with	O
the	O
file	O
itself	O
.	O
</s>
<s>
Multiple	O
data	O
streams	O
also	O
allow	O
Macintosh	B-Device
clients	O
to	O
attach	O
to	O
and	O
use	O
NetWare	B-Operating_System
servers	O
.	O
</s>
<s>
NTFS	B-Application
,	O
the	O
file	B-Application
system	I-Application
introduced	O
with	O
Windows	B-Device
NT	I-Device
3.1	I-Device
,	O
supports	O
file	B-Application
system	I-Application
forks	B-Application
known	O
as	O
alternate	O
data	O
streams	O
(	O
ADS	O
)	O
.	O
</s>
<s>
ReFS	B-Application
,	O
a	O
new	O
file	B-Application
system	I-Application
introduced	O
with	O
Windows	B-Device
Server	I-Device
2012	I-Device
,	O
originally	O
did	O
not	O
support	O
ADS	O
,	O
but	O
in	O
Windows	B-Device
8.1	I-Device
64-bit	O
and	O
Server	B-Device
2012	I-Device
R2	O
,	O
support	O
for	O
ADS	O
,	O
with	O
lengths	O
of	O
up	O
to	O
128K	O
,	O
was	O
added	O
to	O
ReFS	B-Application
.	O
</s>
<s>
ADS	O
was	O
originally	O
intended	O
to	O
add	O
compatibility	O
with	O
existing	O
operating	O
systems	O
that	O
support	O
forks	B-Application
.	O
</s>
<s>
In	O
spite	O
of	O
the	O
support	O
,	O
most	O
programs	O
,	O
including	O
Windows	B-Protocol
Explorer	I-Protocol
and	O
the	O
dir	O
command	O
(	O
before	O
Windows	B-Application
Vista	I-Application
)	O
ignore	O
ADS	O
.	O
</s>
<s>
Windows	B-Protocol
Explorer	I-Protocol
copies	O
ADS	O
and	O
warns	O
when	O
the	O
target	O
file	B-Application
system	I-Application
does	O
not	O
support	O
them	O
,	O
but	O
only	O
calculates	O
the	O
main	O
stream	O
's	O
size	O
and	O
does	O
not	O
list	O
a	O
file	O
or	O
folder	O
's	O
streams	O
.	O
</s>
<s>
Since	O
Windows	B-Application
Vista	I-Application
,	O
the	O
dir	O
command	O
supports	O
showing	O
ADS	O
.	O
</s>
<s>
Windows	B-Application
PowerShell	I-Application
v3.0	O
and	O
later	O
supports	O
manipulating	O
ADS	O
.	O
</s>
<s>
Windows	B-Application
2000	I-Application
uses	O
ADS	O
to	O
store	O
thumbnails	O
in	O
image	O
files	O
,	O
and	O
to	O
store	O
summary	O
information	O
(	O
such	O
as	O
title	O
and	O
author	O
)	O
in	O
any	O
file	O
,	O
without	O
changing	O
the	O
main	O
stream	O
.	O
</s>
<s>
With	O
Windows	B-Application
XP	I-Application
,	O
Microsoft	O
realized	O
that	O
ADS	O
is	O
susceptible	O
to	O
loss	O
when	O
the	O
files	O
containing	O
them	O
are	O
moved	O
off	O
NTFS	B-Application
volumes	O
;	O
thus	O
Windows	B-Application
XP	I-Application
stores	O
them	O
in	O
the	O
main	O
stream	O
whenever	O
the	O
file	O
format	O
supports	O
it	O
.	O
</s>
<s>
Windows	B-Application
Vista	I-Application
discontinued	O
support	O
for	O
adding	O
summary	O
information	O
altogether	O
,	O
as	O
Microsoft	O
decided	O
that	O
they	O
are	O
too	O
sensitive	O
for	O
ADS	O
to	O
handle	O
.	O
</s>
<s>
Service	O
Pack	O
2	O
for	O
Windows	B-Application
XP	I-Application
introduced	O
the	O
Attachment	O
Execution	O
Service	O
that	O
stores	O
details	O
on	O
the	O
origin	O
of	O
downloaded	O
files	O
in	O
an	O
ADS	O
called	O
zone	O
identifier	O
,	O
in	O
an	O
effort	O
to	O
protect	O
users	O
from	O
downloaded	O
files	O
that	O
may	O
present	O
a	O
risk	O
.	O
</s>
<s>
Internet	B-Application
Explorer	I-Application
and	O
Windows	O
8	O
extended	O
this	O
function	O
through	O
SmartScreen	B-Application
.	O
</s>
<s>
Internet	B-Application
Explorer	I-Application
also	O
uses	O
ADS	O
to	O
store	O
favicons	O
in	O
Internet	O
shortcut	O
files	O
.	O
</s>
<s>
Solaris	B-Application
version	O
9	O
and	O
later	O
allows	O
files	O
to	O
have	O
forks	B-Application
.	O
</s>
<s>
Forks	B-Application
are	O
called	O
extended	B-Application
attributes	I-Application
in	O
Solaris	B-Application
,	O
although	O
they	O
are	O
not	O
within	O
the	O
usual	O
meaning	O
of	O
"	O
extended	B-Application
attribute	I-Application
"	O
.	O
</s>
<s>
The	O
maximum	O
size	O
of	O
a	O
Solaris-type	O
extended	B-Application
attribute	I-Application
is	O
the	O
same	O
as	O
the	O
maximum	O
size	O
of	O
a	O
file	O
,	O
and	O
they	O
are	O
read	O
and	O
written	O
in	O
the	O
same	O
fashion	O
as	O
files	O
.	O
</s>
<s>
Extended	B-Application
attributes	I-Application
in	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
Version	O
4	O
are	O
similar	O
to	O
Solaris-style	O
extended	B-Application
attributes	I-Application
.	O
</s>
<s>
When	O
a	O
file	B-Application
system	I-Application
supports	O
different	O
forks	B-Application
,	O
the	O
applications	O
should	O
be	O
aware	O
of	O
them	O
,	O
or	O
security	O
risks	O
can	O
arise	O
.	O
</s>
<s>
Allowing	O
legacy	B-Device
software	I-Device
to	O
access	O
data	O
without	O
appropriate	O
shims	B-General_Concept
in	O
place	O
is	O
the	O
primary	O
culprit	O
for	O
such	O
problems	O
.	O
</s>
<s>
If	O
the	O
different	O
system	O
utilities	O
(	O
disk	O
explorer	O
,	O
antivirus	O
software	O
,	O
archivers	O
,	O
and	O
so	O
on	O
)	O
,	O
are	O
not	O
aware	O
of	O
the	O
different	O
forks	B-Application
,	O
the	O
following	O
problems	O
can	O
arise	O
:	O
</s>
<s>
The	O
user	O
will	O
never	O
know	O
the	O
presence	O
of	O
any	O
alternate	O
fork	B-Application
nor	O
the	O
total	O
size	O
of	O
the	O
file	O
,	O
just	O
of	O
the	O
main	O
data	B-Operating_System
fork	I-Operating_System
.	O
</s>
<s>
Computer	O
viruses	O
can	O
hide	O
in	O
alternate	O
forks	B-Application
on	O
Windows	O
and	O
never	O
get	O
detected	O
if	O
the	O
antivirus	O
software	O
is	O
not	O
aware	O
of	O
forks	B-Application
.	O
</s>
<s>
Data	O
can	O
be	O
lost	O
when	O
sending	O
files	O
via	O
fork-unaware	O
channels	O
,	O
such	O
as	O
e-mail	O
,	O
file	B-Application
systems	I-Application
without	O
support	O
for	O
forks	B-Application
,	O
or	O
even	O
when	O
copying	O
files	O
between	O
file	B-Application
systems	I-Application
with	O
forks	B-Application
support	O
if	O
the	O
program	O
that	O
made	O
the	O
copy	O
does	O
not	O
support	O
forks	B-Application
or	O
when	O
compressing	O
files	O
with	O
software	O
that	O
does	O
not	O
support	O
forks	B-Application
.	O
</s>
