<s>
In	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
a	O
device	B-Application
file	I-Application
or	O
special	B-Application
file	I-Application
is	O
an	O
interface	B-Application
to	O
a	O
device	B-Application
driver	I-Application
that	O
appears	O
in	O
a	O
file	B-Application
system	I-Application
as	O
if	O
it	O
were	O
an	O
ordinary	O
file	B-Operating_System
.	O
</s>
<s>
There	O
are	O
also	O
special	B-Application
files	I-Application
in	O
DOS	B-Device
,	O
OS/2	B-Application
,	O
and	O
Windows	O
.	O
</s>
<s>
These	O
special	B-Application
files	I-Application
allow	O
an	O
application	O
program	O
to	O
interact	O
with	O
a	O
device	O
by	O
using	O
its	O
device	B-Application
driver	I-Application
via	O
standard	O
input/output	B-General_Concept
system	B-Operating_System
calls	I-Operating_System
.	O
</s>
<s>
Using	O
standard	O
system	B-Operating_System
calls	I-Operating_System
simplifies	O
many	O
programming	O
tasks	O
,	O
and	O
leads	O
to	O
consistent	O
user-space	B-Operating_System
I/O	B-General_Concept
mechanisms	O
regardless	O
of	O
device	O
features	O
and	O
functions	O
.	O
</s>
<s>
Device	B-Application
files	I-Application
usually	O
provide	O
simple	O
interfaces	B-Application
to	O
standard	O
devices	O
(	O
such	O
as	O
printers	O
and	O
serial	B-Protocol
ports	I-Protocol
)	O
,	O
but	O
can	O
also	O
be	O
used	O
to	O
access	O
specific	O
unique	O
resources	O
on	O
those	O
devices	O
,	O
such	O
as	O
disk	B-Application
partitions	I-Application
.	O
</s>
<s>
Additionally	O
,	O
device	B-Application
files	I-Application
are	O
useful	O
for	O
accessing	O
system	B-General_Concept
resources	I-General_Concept
that	O
have	O
no	O
connection	O
with	O
any	O
actual	O
device	O
,	O
such	O
as	O
data	B-Application
sinks	I-Application
and	O
random	O
number	O
generators	O
.	O
</s>
<s>
There	O
are	O
two	O
general	O
kinds	O
of	O
device	B-Application
files	I-Application
in	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
known	O
as	O
character	O
special	B-Application
files	I-Application
and	O
block	O
special	B-Application
files	I-Application
.	O
</s>
<s>
The	O
difference	O
between	O
them	O
lies	O
in	O
how	O
much	O
data	O
is	O
read	O
and	O
written	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
and	O
hardware	O
.	O
</s>
<s>
These	O
together	O
can	O
be	O
called	O
device	B-Application
special	I-Application
files	I-Application
in	O
contrast	O
to	O
named	B-Operating_System
pipes	I-Operating_System
,	O
which	O
are	O
not	O
connected	O
to	O
a	O
device	O
but	O
are	O
not	O
ordinary	O
files	O
either	O
.	O
</s>
<s>
MS-DOS	B-Application
borrowed	O
the	O
concept	O
of	O
special	B-Application
files	I-Application
from	O
Unix	O
but	O
renamed	O
them	O
devices	O
.	O
</s>
<s>
Because	O
early	O
versions	O
of	O
MS-DOS	B-Application
did	O
not	O
support	O
a	O
directory	B-Application
hierarchy	O
,	O
devices	O
were	O
distinguished	O
from	O
regular	O
files	O
by	O
making	O
their	O
names	O
reserved	O
words	O
,	O
for	O
example	O
:	O
the	O
infamous	O
CON	O
.	O
</s>
<s>
These	O
were	O
chosen	O
for	O
a	O
degree	O
of	O
compatibility	O
with	O
CP/M	B-Application
and	O
are	O
still	O
present	O
in	O
modern	O
Windows	O
for	O
backwards	O
compatibility	O
.	O
</s>
<s>
In	O
some	O
Unix-like	B-Operating_System
systems	I-Operating_System
,	O
most	O
device	B-Application
files	I-Application
are	O
managed	O
as	O
part	O
of	O
a	O
virtual	B-Application
file	I-Application
system	I-Application
traditionally	O
mounted	O
at	O
/dev	B-Application
,	O
possibly	O
associated	O
with	O
a	O
controlling	O
daemon	O
,	O
which	O
monitors	O
hardware	O
addition	O
and	O
removal	O
at	O
run	O
time	O
,	O
making	O
corresponding	O
changes	O
to	O
the	O
device	B-Application
file	I-Application
system	O
if	O
that	O
's	O
not	O
automatically	O
done	O
by	O
the	O
kernel	B-Operating_System
,	O
and	O
possibly	O
invoking	O
scripts	O
in	O
system	O
or	O
user	B-Operating_System
space	I-Operating_System
to	O
handle	O
special	O
device	O
needs	O
.	O
</s>
<s>
The	O
FreeBSD	B-Operating_System
,	O
DragonFly	B-Application
BSD	I-Application
and	O
Darwin	B-Operating_System
have	O
a	O
dedicated	O
file	B-Application
system	I-Application
devfs	O
;	O
device	B-Application
nodes	I-Application
are	O
managed	O
automatically	O
by	O
this	O
file	B-Application
system	I-Application
,	O
in	O
kernel	B-Operating_System
space	I-Operating_System
.	O
</s>
<s>
Linux	B-Application
used	O
to	O
have	O
a	O
similar	O
devfs	O
implementation	O
,	O
but	O
it	O
was	O
abandoned	O
later	O
,	O
and	O
then	O
removed	O
since	O
version	O
2.6.17	O
;	O
Linux	B-Application
now	O
primarily	O
uses	O
a	O
user	B-Operating_System
space	I-Operating_System
implementation	O
known	O
as	O
udev	B-Application
,	O
but	O
there	O
are	O
many	O
variants	O
.	O
</s>
<s>
In	O
Unix	O
systems	O
which	O
support	O
chroot	B-Application
process	O
isolation	O
,	O
such	O
as	O
Solaris	B-Application
Containers	O
,	O
typically	O
each	O
chroot	B-Application
environment	I-Application
needs	O
its	O
own	O
/dev	B-Application
;	O
these	O
mount	O
points	O
will	O
be	O
visible	O
on	O
the	O
host	O
OS	O
at	O
various	O
nodes	O
in	O
the	O
global	O
file	B-Application
system	I-Application
tree	O
.	O
</s>
<s>
By	O
restricting	O
the	O
device	B-Application
nodes	I-Application
populated	O
into	O
chroot	B-Application
instances	O
of	O
/dev	B-Application
,	O
hardware	O
isolation	O
can	O
be	O
enforced	O
by	O
the	O
chroot	B-Application
environment	I-Application
(	O
a	O
program	O
can	O
not	O
meddle	O
with	O
hardware	O
that	O
it	O
can	O
neither	O
see	O
nor	O
name	O
—	O
an	O
even	O
stronger	O
form	O
of	O
access	O
control	O
than	O
Unix	O
file	B-Application
system	I-Application
permissions	O
)	O
.	O
</s>
<s>
MS-DOS	B-Application
managed	O
hardware	O
device	O
contention	O
(	O
see	O
terminate-and-stay-resident	O
program	O
)	O
by	O
making	O
each	O
device	B-Application
file	I-Application
exclusive	O
open	O
.	O
</s>
<s>
An	O
application	O
attempting	O
to	O
access	O
a	O
device	O
already	O
in	O
use	O
would	O
discover	O
itself	O
unable	O
to	O
open	O
the	O
device	B-Application
file	I-Application
node	B-Data_Structure
.	O
</s>
<s>
A	O
variety	O
of	O
device	B-Application
driver	I-Application
semantics	O
are	O
implemented	O
in	O
Unix	O
and	O
Linux	B-Application
concerning	O
concurrent	B-Operating_System
access	I-Operating_System
.	O
</s>
<s>
Device	B-Application
nodes	I-Application
correspond	O
to	O
resources	O
that	O
an	O
operating	B-General_Concept
system	I-General_Concept
's	O
kernel	B-Operating_System
has	O
already	O
allocated	O
.	O
</s>
<s>
Unix	O
identifies	O
those	O
resources	O
by	O
a	O
major	O
number	O
and	O
a	O
minor	O
number	O
,	O
both	O
stored	O
as	O
part	O
of	O
the	O
structure	O
of	O
a	O
node	B-Data_Structure
.	O
</s>
<s>
The	O
assignment	O
of	O
these	O
numbers	O
occurs	O
uniquely	O
in	O
different	O
operating	B-General_Concept
systems	I-General_Concept
and	O
on	O
different	O
computer	B-Device
platforms	I-Device
.	O
</s>
<s>
Generally	O
,	O
the	O
major	O
number	O
identifies	O
the	O
device	B-Application
driver	I-Application
and	O
the	O
minor	O
number	O
identifies	O
a	O
particular	O
device	O
(	O
possibly	O
out	O
of	O
many	O
)	O
that	O
the	O
driver	O
controls	O
:	O
in	O
this	O
case	O
,	O
the	O
system	O
may	O
pass	O
the	O
minor	O
number	O
to	O
a	O
driver	O
.	O
</s>
<s>
on	O
FreeBSD	B-Operating_System
5	O
and	O
up	O
)	O
.	O
</s>
<s>
As	O
with	O
other	O
special	B-Application
file	I-Application
types	O
,	O
the	O
computer	O
system	O
accesses	O
device	B-Application
nodes	I-Application
using	O
standard	O
system	B-Operating_System
calls	I-Operating_System
and	O
treats	O
them	O
like	O
regular	O
computer	B-Operating_System
files	I-Operating_System
.	O
</s>
<s>
Two	O
standard	O
types	O
of	O
device	B-Application
files	I-Application
exist	O
;	O
unfortunately	O
their	O
names	O
are	O
rather	O
counter-intuitive	O
for	O
historical	O
reasons	O
,	O
and	O
explanations	O
of	O
the	O
difference	O
between	O
the	O
two	O
are	O
often	O
incorrect	O
as	O
a	O
result	O
.	O
</s>
<s>
Character	O
special	B-Application
files	I-Application
or	O
character	O
devices	O
provide	O
unbuffered	O
,	O
direct	O
access	O
to	O
the	O
hardware	O
device	O
.	O
</s>
<s>
The	O
character	O
device	O
for	O
a	O
hard	B-Device
disk	I-Device
,	O
for	O
example	O
,	O
will	O
normally	O
require	O
that	O
all	O
reads	O
and	O
writes	O
be	O
aligned	O
to	O
block	O
boundaries	O
and	O
most	O
certainly	O
will	O
not	O
allow	O
reading	O
a	O
single	O
byte	O
.	O
</s>
<s>
Block	O
special	B-Application
files	I-Application
or	O
block	O
devices	O
provide	O
buffered	O
access	O
to	O
hardware	O
devices	O
,	O
and	O
provide	O
some	O
abstraction	O
from	O
their	O
specifics	O
.	O
</s>
<s>
The	O
downside	O
is	O
that	O
because	O
block	O
devices	O
are	O
buffered	O
,	O
the	O
programmer	O
does	O
not	O
know	O
how	O
long	O
it	O
will	O
take	O
before	O
written	O
data	O
is	O
passed	O
from	O
the	O
kernel	B-Operating_System
's	O
buffers	B-General_Concept
to	O
the	O
actual	O
device	O
,	O
or	O
indeed	O
in	O
what	O
order	O
two	O
separate	O
writes	O
will	O
arrive	O
at	O
the	O
physical	B-Device
device	I-Device
.	O
</s>
<s>
Additionally	O
,	O
if	O
the	O
same	O
hardware	O
exposes	O
both	O
character	O
and	O
block	O
devices	O
,	O
there	O
is	O
a	O
risk	O
of	O
data	O
corruption	O
due	O
to	O
clients	O
using	O
the	O
character	O
device	O
being	O
unaware	O
of	O
changes	O
made	O
in	O
the	O
buffers	B-General_Concept
of	O
the	O
block	O
device	O
.	O
</s>
<s>
Most	O
systems	O
create	O
both	O
block	O
and	O
character	O
devices	O
to	O
represent	O
hardware	O
like	O
hard	B-Device
disks	I-Device
.	O
</s>
<s>
FreeBSD	B-Operating_System
and	O
Linux	B-Application
notably	O
do	O
not	O
;	O
the	O
former	O
has	O
removed	O
support	O
for	O
block	O
devices	O
,	O
while	O
the	O
latter	O
creates	O
only	O
block	O
devices	O
.	O
</s>
<s>
In	O
Linux	B-Application
,	O
to	O
get	O
a	O
character	O
device	O
for	O
a	O
disk	O
,	O
one	O
must	O
use	O
the	O
"	O
raw	O
"	O
driver	O
,	O
though	O
one	O
can	O
get	O
the	O
same	O
effect	O
as	O
opening	O
a	O
character	O
device	O
by	O
opening	O
the	O
block	O
device	O
with	O
the	O
Linux-specific	O
flag	O
.	O
</s>
<s>
Device	B-Application
nodes	I-Application
on	O
Unix-like	B-Operating_System
systems	I-Operating_System
do	O
not	O
necessarily	O
have	O
to	O
correspond	O
to	O
physical	B-Device
devices	I-Device
.	O
</s>
<s>
They	O
provide	O
various	O
functions	O
handled	O
by	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
accepts	O
and	O
discards	O
all	O
input	O
written	O
to	O
it	O
;	O
provides	O
an	O
end-of-file	B-Language
indication	O
when	O
read	O
from	O
.	O
</s>
<s>
produces	O
bytes	O
generated	O
by	O
the	O
kernel	B-Operating_System
's	O
cryptographically	B-Algorithm
secure	I-Algorithm
pseudorandom	I-Algorithm
number	I-Algorithm
generator	I-Algorithm
.	O
</s>
<s>
,	O
,	O
access	O
the	O
process	O
's	O
standard	B-Operating_System
streams	I-Operating_System
.	O
</s>
<s>
n	O
accesses	O
the	O
process	O
's	O
file	B-Application
descriptor	I-Application
n	O
.	O
</s>
<s>
Additionally	O
,	O
BSD-specific	O
pseudo-devices	O
with	O
an	O
interface	B-Application
may	O
also	O
include	O
:	O
</s>
<s>
allows	O
userland	O
processes	O
to	O
control	O
PF	B-Protocol
through	O
an	O
interface	B-Application
.	O
</s>
<s>
provides	O
access	O
to	O
devices	O
otherwise	O
not	O
found	O
as	O
nodes	O
,	O
used	O
by	O
to	O
implement	O
RAID	B-Architecture
management	O
in	O
OpenBSD	B-Operating_System
and	O
NetBSD	B-Device
.	O
</s>
<s>
used	O
by	O
NetBSD	B-Device
's	O
envsys	B-Device
framework	O
for	O
hardware	B-Application
monitoring	I-Application
,	O
accessed	O
in	O
the	O
userland	O
through	O
by	O
the	O
utility	O
.	O
</s>
<s>
Nodes	O
are	O
created	O
by	O
the	O
system	B-Operating_System
call	I-Operating_System
.	O
</s>
<s>
Nodes	O
can	O
be	O
moved	O
or	O
deleted	O
by	O
the	O
usual	O
filesystem	B-Application
system	B-Operating_System
calls	I-Operating_System
(	O
,	O
)	O
and	O
commands	B-Application
(	O
,	O
)	O
.	O
</s>
<s>
Some	O
Unix	O
versions	O
include	O
a	O
script	O
named	O
makedev	O
or	O
MAKEDEV	O
to	O
create	O
all	O
necessary	O
devices	O
in	O
the	O
directory	B-Application
.	O
</s>
<s>
It	O
only	O
makes	O
sense	O
on	O
systems	O
whose	O
devices	O
are	O
statically	O
assigned	O
major	O
numbers	O
(	O
e.g.	O
,	O
by	O
means	O
of	O
hardcoding	O
it	O
in	O
their	O
kernel	B-Operating_System
module	O
)	O
.	O
</s>
<s>
While	O
some	O
other	O
Unix	O
systems	O
such	O
as	O
FreeBSD	B-Operating_System
,	O
used	O
kernel-based	O
device	B-Application
node	I-Application
management	O
via	O
devfs	O
only	O
,	O
and	O
not	O
supporting	O
manual	O
node	B-Data_Structure
creation	O
.	O
</s>
<s>
system	B-Operating_System
call	I-Operating_System
and	O
command	O
exist	O
to	O
keep	O
compatibility	O
with	O
POSIX	O
,	O
but	O
manually	O
created	O
device	B-Application
nodes	I-Application
outside	O
devfs	O
will	O
not	O
function	O
at	O
all	O
.	O
</s>
<s>
Some	O
additional	O
prefixes	O
have	O
come	O
into	O
common	O
use	O
in	O
some	O
operating	B-General_Concept
systems	I-General_Concept
:	O
</s>
<s>
:	O
(	O
"	O
classic	O
"	O
)	O
IDE	B-Protocol
driver	O
(	O
previously	O
used	O
for	O
ATA	O
hard	B-Device
disk	I-Device
drive	I-Device
,	O
ATAPI	O
optical	O
disc	O
drives	O
,	O
etc	O
.	O
)	O
</s>
<s>
NVMe	B-Application
driver	O
:	O
</s>
<s>
:	O
storage	O
driver	O
for	O
MMC	O
media	O
(	O
SD	B-Device
cards	I-Device
,	O
eMMC	O
chips	O
on	O
laptops	O
,	O
etc	O
.	O
)	O
</s>
<s>
SCSI	B-Architecture
driver	O
,	O
also	O
used	O
by	O
libATA	B-Application
(	O
modern	O
PATA/SATA	O
driver	O
)	O
,	O
USB	B-Protocol
,	O
IEEE	B-Protocol
1394	I-Protocol
,	O
etc	O
.	O
</s>
<s>
:	O
USB	B-Protocol
serial	O
converters	O
,	O
modems	O
,	O
etc	O
.	O
</s>
<s>
The	O
canonical	O
list	O
of	O
the	O
prefixes	O
used	O
in	O
Linux	B-Application
can	O
be	O
found	O
in	O
the	O
Linux	B-Application
Device	O
List	O
,	O
the	O
official	O
registry	O
of	O
allocated	O
device	O
numbers	O
and	O
directory	B-Application
nodes	O
for	O
the	O
Linux	B-Application
operating	I-Application
system	I-Application
.	O
</s>
<s>
For	O
hard	B-Device
drives	I-Device
,	O
a	O
letter	O
is	O
used	O
to	O
identify	O
devices	O
and	O
is	O
followed	O
by	O
a	O
number	O
to	O
identify	O
partitions	B-Application
.	O
</s>
<s>
Thus	O
a	O
file	B-Application
system	I-Application
may	O
"	O
know	O
"	O
an	O
area	O
on	O
a	O
disk	O
as	O
,	O
for	O
example	O
,	O
or	O
"	O
see	O
"	O
a	O
networked	O
terminal	B-General_Concept
session	O
as	O
associated	O
with	O
.	O
</s>
<s>
On	O
disks	O
using	O
the	O
typical	O
PC	O
master	B-Device
boot	I-Device
record	I-Device
,	O
the	O
device	O
numbers	O
of	O
primary	O
and	O
the	O
optional	O
extended	O
partition	B-Application
are	O
numbered	O
1	O
through	O
4	O
,	O
while	O
the	O
indexes	O
of	O
any	O
logical	O
partitions	B-Application
are	O
5	O
and	O
onwards	O
,	O
regardless	O
of	O
the	O
layout	O
of	O
the	O
former	O
partitions	B-Application
(	O
their	O
parent	O
extended	O
partition	B-Application
does	O
not	O
need	O
to	O
be	O
the	O
fourth	O
partition	B-Application
on	O
the	O
disk	O
,	O
nor	O
do	O
all	O
four	O
primary	O
partitions	B-Application
have	O
to	O
exist	O
)	O
.	O
</s>
<s>
Device	B-Application
names	I-Application
are	O
usually	O
not	O
portable	O
between	O
different	O
Unix-like	B-Operating_System
system	I-Operating_System
variants	O
,	O
for	O
example	O
,	O
on	O
some	O
BSD	B-Operating_System
systems	O
,	O
the	O
IDE	B-Protocol
devices	O
are	O
named	O
,	O
,	O
etc	O
.	O
</s>
<s>
devfs	O
is	O
a	O
specific	O
implementation	O
of	O
a	O
device	B-Application
file	I-Application
system	O
on	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
,	O
used	O
for	O
presenting	O
device	B-Application
files	I-Application
.	O
</s>
<s>
Maintaining	O
these	O
special	B-Application
files	I-Application
on	O
a	O
physically-implemented	O
file	B-Application
system	I-Application
such	O
as	O
a	O
hard	B-Device
drive	I-Device
is	O
inconvenient	O
,	O
and	O
as	O
it	O
needs	O
kernel	B-Operating_System
assistance	O
anyway	O
,	O
the	O
idea	O
arose	O
of	O
a	O
special-purpose	O
logical	O
file	B-Application
system	I-Application
that	O
is	O
not	O
physically	O
stored	O
.	O
</s>
<s>
The	O
devfs	O
approach	O
is	O
for	O
the	O
device	B-Application
driver	I-Application
to	O
request	O
creation	O
and	O
deletion	O
of	O
devfs	O
entries	O
related	O
to	O
the	O
devices	O
it	O
enables	O
and	O
disables	O
.	O
</s>
<s>
A	O
device	B-Application
file	I-Application
is	O
a	O
reserved	O
keyword	O
used	O
in	O
PC	B-Operating_System
DOS	I-Operating_System
,	O
TOS	B-Application
,	O
OS/2	B-Application
,	O
and	O
Windows	O
systems	O
to	O
allow	O
access	O
to	O
certain	O
ports	O
and	O
devices	O
.	O
</s>
<s>
MS-DOS	B-Application
borrowed	O
the	O
concept	O
of	O
special	B-Application
files	I-Application
from	O
Unix	O
but	O
renamed	O
them	O
devices	O
.	O
</s>
<s>
Because	O
early	O
versions	O
of	O
MS-DOS	B-Application
did	O
not	O
support	O
a	O
directory	B-Application
hierarchy	O
,	O
devices	O
were	O
distinguished	O
from	O
regular	O
files	O
by	O
making	O
their	O
names	O
reserved	O
words	O
.	O
</s>
<s>
This	O
means	O
that	O
certain	O
file	B-Operating_System
names	O
were	O
reserved	O
for	O
devices	O
,	O
and	O
should	O
not	O
be	O
used	O
to	O
name	O
new	O
files	O
or	O
directories	B-Application
.	O
</s>
<s>
The	O
reserved	O
names	O
themselves	O
were	O
chosen	O
to	O
be	O
compatible	O
with	O
"	O
special	B-Application
files	I-Application
"	O
handling	O
of	O
PIP	B-Application
command	O
in	O
CP/M	B-Application
.	O
</s>
<s>
There	O
were	O
two	O
kinds	O
of	O
devices	O
in	O
DOS	B-Device
:	O
Block	O
Devices	O
(	O
used	O
for	O
disk	O
drives	O
)	O
and	O
Character	O
Devices	O
(	O
generally	O
all	O
other	O
devices	O
,	O
including	O
COM	O
and	O
PRN	B-Application
devices	O
)	O
.	O
</s>
<s>
DOS	B-Device
uses	O
device	B-Application
files	I-Application
for	O
accessing	O
printers	O
and	O
ports	O
.	O
</s>
<s>
Versions	O
2.x	O
of	O
MS-DOS	B-Application
provide	O
the	O
AVAILDEV	B-Device
CONFIG.SYS	B-Device
parameter	O
that	O
,	O
if	O
set	O
to	O
FALSE	O
,	O
makes	O
these	O
special	O
names	O
only	O
active	O
if	O
prefixed	O
with	O
\DEV\,	O
thus	O
allowing	O
ordinary	O
files	O
to	O
be	O
created	O
with	O
these	O
names	O
.	O
</s>
<s>
GEMDOS	B-Operating_System
,	O
the	O
DOS-like	O
part	O
of	O
Atari	B-Application
TOS	I-Application
,	I-Application
supported	O
similar	O
device	B-Application
names	I-Application
to	O
DOS	B-Device
,	O
but	O
unlike	O
DOS	B-Device
it	O
required	O
a	O
trailing	O
"	O
:	O
"	O
character	O
(	O
on	O
DOS	B-Device
,	O
this	O
is	O
optional	O
)	O
to	O
identify	O
them	O
as	O
devices	O
as	O
opposed	O
to	O
normal	O
filenames	O
(	O
thus	O
"	O
CON	B-Application
:	I-Application
"	O
would	O
work	O
on	O
both	O
DOS	B-Device
and	O
TOS	B-Application
,	O
but	O
"	O
CON	O
"	O
would	O
name	O
an	O
ordinary	O
file	B-Operating_System
on	O
TOS	B-Application
but	O
the	O
console	O
device	O
on	O
DOS	B-Device
)	O
.	O
</s>
<s>
In	O
MiNT	B-Application
and	O
MagiC	O
,	O
a	O
special	O
UNIX-like	B-Operating_System
unified	O
filesystem	B-Application
view	O
accessed	O
via	O
the	O
"	O
U	O
:	O
"	O
drive	O
letter	O
also	O
placed	O
device	B-Application
files	I-Application
in	O
"	O
U:\DEV	O
 "	O
.	O
</s>
<s>
PRN	B-Application
Prints	O
text	O
to	O
the	O
printer	O
,	O
usually	O
redirected	O
to	O
LPT1	O
or	O
LST	B-Application
.	O
</s>
<s>
AUX	B-Application
(	O
not	O
in	O
OS/2	B-Application
)	O
Reads	O
data	O
from	O
an	O
auxiliary	O
device	O
,	O
usually	O
a	O
serial	O
device	O
like	O
COM1	O
.	O
</s>
<s>
NUL	B-Application
Returns	O
null	O
or	O
no	O
data	O
.	O
</s>
<s>
KEYBD$	O
(	O
only	O
in	O
multitasking	B-Application
MS-DOS	I-Application
)	O
KBD$	B-Device
(	O
only	O
in	O
OS/2	B-Application
)	O
SCREEN$	B-Device
(	O
only	O
in	O
multitasking	B-Application
MS-DOS	I-Application
and	O
OS/2	B-Application
)	O
POINTER$	B-Device
(	O
only	O
in	O
OS/2	B-Application
)	O
MOUSE$	B-Device
(	O
only	O
in	O
OS/2	B-Application
)	O
$IDLE$	O
(	O
only	O
in	O
DR-DOS	B-Application
(	O
since	O
5.0	O
)	O
and	O
Multiuser	B-Operating_System
DOS	I-Operating_System
(	O
since	O
Concurrent	B-Operating_System
DOS	I-Operating_System
386	I-Operating_System
)	O
families	O
)	O
CONFIG$	O
(	O
only	O
in	O
MS-DOS	B-Application
7.0	O
and	O
higher	O
)	O
LST	B-Application
(	O
only	O
in	O
86-DOS	B-Operating_System
and	O
DOS	B-Device
1.x	O
,	O
also	O
in	O
Hewlett-Packard	O
'	O
s	O
MS-DOS	B-Application
2.11	O
for	O
the	O
HP	O
Portable	O
Plus	O
)	O
Returns	O
no	O
data	O
.	O
</s>
<s>
(	O
LPT2	O
for	O
Hewlett-Packard	O
'	O
s	O
MS-DOS	B-Application
2.11	O
)	O
PLT	O
(	O
only	O
in	O
Hewlett-Packard	O
'	O
s	O
MS-DOS	B-Application
2.11	O
for	O
the	O
HP	O
Portable	O
Plus	O
)	O
Returns	O
no	O
data	O
.	O
</s>
<s>
Sends	O
data	O
to	O
the	O
assigned	O
plotter	B-Operating_System
.	O
</s>
<s>
The	O
attached	O
plotter	B-Operating_System
device	O
is	O
reconfigurable	O
.	O
</s>
<s>
LPT1	O
,	O
LPT2	O
,	O
LPT3	O
,	O
and	O
sometimes	O
LPT4	O
(	O
in	O
DR-DOS	B-Application
7.02	O
and	O
higher	O
and	O
some	O
versions	O
of	O
Multiuser	B-Operating_System
DOS	I-Operating_System
)	O
Sends	O
data	O
to	O
the	O
selected	O
parallel	B-Device
port	I-Device
.	O
</s>
<s>
COM1	O
,	O
COM2	O
,	O
COM3	O
,	O
COM4	O
Reads	O
data	O
from	O
the	O
selected	O
serial	B-Protocol
port	I-Protocol
.	O
</s>
<s>
Sends	O
data	O
to	O
the	O
selected	O
serial	B-Protocol
port	I-Protocol
.	O
</s>
<s>
82164A	O
(	O
only	O
in	O
Hewlett-Packard	O
'	O
s	O
MS-DOS	B-Application
2.11	O
for	O
the	O
HP	O
Portable	O
Plus	O
)	O
Redirects	O
to	O
COM2	O
.	O
</s>
<s>
Using	O
shell	O
redirection	B-Device
and	O
pipes	O
,	O
data	O
can	O
be	O
sent	O
to	O
or	O
received	O
from	O
a	O
device	O
.	O
</s>
<s>
For	O
example	O
,	O
typing	O
the	O
following	O
will	O
send	O
the	O
file	B-Operating_System
c:\data.txt	O
to	O
the	O
printer	O
:	O
</s>
<s>
The	O
8-bit	O
operating	B-General_Concept
system	I-General_Concept
of	O
Sharp	O
pocket	B-Device
computers	I-Device
like	O
the	O
PC-E500	B-Device
,	O
PC-E500S	B-Device
etc	O
.	O
</s>
<s>
consists	O
of	O
a	O
BASIC	O
interpreter	O
,	O
a	O
DOS	B-Device
2-like	O
File	B-Operating_System
Control	O
System	O
(	O
FCS	O
)	O
implementing	O
a	O
rudimentary	O
12-bit	O
FAT-like	O
filesystem	B-Application
,	O
and	O
a	O
BIOS-like	O
Input/Output	B-Application
Control	I-Application
System	I-Application
(	O
IOCS	B-Application
)	O
implementing	O
a	O
number	O
of	O
standard	O
character	O
and	O
block	O
device	B-Application
drivers	I-Application
as	O
well	O
as	O
special	B-Application
file	I-Application
devices	O
including	O
STDO:/SCRN	O
:	O
(	O
display	O
)	O
,	O
STDI:/KYBD	O
:	O
(	O
keyboard	O
)	O
,	O
COM	O
:	O
(	O
serial	O
I/O	B-General_Concept
)	O
,	O
STDL:/PRN	O
:	O
(	O
printer	O
)	O
,	O
CAS	O
:	O
(	O
cassette	O
tape	O
)	O
,	O
E:/F:/G	O
:	O
(	O
memory	O
file	B-Operating_System
)	O
,	O
S1:/S2:/S3	O
:	O
(	O
memory	O
card	O
)	O
,	O
X:/Y	O
:	O
(	O
floppy	B-Device
)	O
,	O
SYSTM	O
:	O
(	O
system	O
)	O
,	O
and	O
NIL	B-Operating_System
:	I-Operating_System
(	O
function	O
)	O
.	O
</s>
<s>
Operating	B-General_Concept
System	I-General_Concept
Filesystem	B-Application
or	O
managing	O
software	O
Standard	O
mount	O
point	O
Author	O
Notes	O
Linux	B-Application
2.3.46pre5	O
–	O
2.6.17	O
devfs	O
and	O
devfsd	B-Application
/dev	B-Application
Richard	O
Gooch	O
Implemented	O
fully	O
in	O
the	O
kernel	B-Operating_System
,	O
with	O
optional	O
daemon	O
devfsd	B-Application
to	O
handle	O
device	B-Application
node	I-Application
events	O
in	O
user	B-Operating_System
space	I-Operating_System
.	O
</s>
<s>
Obsolete	O
–	O
users	O
are	O
encouraged	O
to	O
migrate	O
to	O
udev	B-Application
and/or	O
devtmpfs	B-Application
.	O
</s>
<s>
Linux	B-Application
2.5	O
–	O
udev	B-Application
on	O
any	O
fs	O
,	O
but	O
usually	O
tmpfs	B-Application
/dev	B-Application
Greg	O
Kroah-Hartman	O
,	O
Kay	O
Sievers	O
and	O
Dan	O
Stekloff	O
Implemented	O
largely	O
in	O
user	B-Operating_System
space	I-Operating_System
,	O
device	O
information	O
is	O
gathered	O
from	O
sysfs	B-Application
.	O
</s>
<s>
Device	B-Application
files	I-Application
can	O
be	O
stored	O
on	O
a	O
conventional	O
general-purpose	O
file	B-Application
system	I-Application
,	O
or	O
in	O
a	O
memory	O
file	B-Application
system	I-Application
(	O
tmpfs	B-Application
)	O
.	O
</s>
<s>
Linux	O
2.6.32	O
–	O
devtmpfs	B-Application
with	O
or	O
without	O
udev	B-Application
/dev	B-Application
Kay	O
Sievers	O
,	O
Jan	O
Blunck	O
,	O
Greg	O
Kroah-Hartman	O
A	O
hybrid	O
kernel/userspace	O
approach	O
of	O
a	O
device	O
filesystem	B-Application
to	O
provide	O
nodes	O
before	O
udev	B-Application
runs	O
for	O
the	O
first	O
time	O
Solaris	B-Application
devfs	O
/devices	O
Sun	O
Microsystems	O
Introduced	O
with	O
dynamic	O
loaded	O
drivers	O
in	O
Solaris-2.1	O
FreeBSD	B-Operating_System
2.0	O
–	O
devfs	O
/dev	B-Application
Poul-Henning	O
Kamp	O
Implemented	O
fully	O
in	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
DragonFly	B-Application
BSD	I-Application
2.3.2	O
–	O
devfs	O
/dev	B-Application
Alex	O
Hornung	O
Implemented	O
fully	O
in	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
macOS	B-Application
devfs	O
/dev	B-Application
Apple	O
Inc	O
.	O
</s>
<s>
Implemented	O
fully	O
in	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
HP-UX	B-Application
B.11.31	O
devfs	O
/dev	B-Application
HP	O
Implemented	O
fully	O
in	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
Plan	B-Operating_System
9	I-Operating_System
#	O
Bell	O
Labs	O
Implemented	O
in	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
RISC	B-Operating_System
OS	I-Operating_System
DeviceFS	O
Devices	O
:	O
Acorn	O
Computers	O
DeviceFS	O
was	O
started	O
in	O
1991	O
and	O
first	O
appeared	O
in	O
RISC	B-Operating_System
OS	I-Operating_System
3	O
.	O
</s>
<s>
It	O
manages	O
several	O
device	O
like	O
special	B-Application
files	I-Application
,	O
most	O
commonly	O
:	O
Parallel	O
,	O
Serial	O
,	O
FastParallel	O
,	O
and	O
USB	B-Protocol
.	O
</s>
<s>
The	O
SystemDevices	O
module	O
implements	O
the	O
pseudo	B-Application
devices	I-Application
such	O
as	O
:	O
Vdu	O
,	O
Kbd	O
,	O
Null	O
and	O
Printer	O
.	O
</s>
<s>
MS-DOS	B-Application
,	O
PC	O
DOS	B-Device
,	O
DR-DOS	B-Application
FAT	B-Application
\DEV	O
(	O
and	O
/DEV	B-Application
)	O
various	O
As	O
implemented	O
in	O
the	O
kernel	B-Operating_System
,	O
character	O
devices	O
appear	O
in	O
the	O
virtual	O
\DEV	O
directory	B-Application
and	O
any	O
disk	O
directory	B-Application
.	O
</s>
<s>
Under	O
MS-DOS/PC	O
DOS	B-Device
2.x	O
,	O
the	O
CONFIG.SYS	B-Device
AVAILDEV	B-Device
=	O
FALSE	O
directive	O
can	O
be	O
used	O
to	O
force	O
devices	O
to	O
exist	O
only	O
in	O
\DEV	O
.	O
</s>
<s>
MagiC	O
,	O
MiNT	B-Application
,	O
MultiTOS	B-Application
U:\DEV	O
Application	O
Systems	O
Heidelberg	O
,	O
Eric	O
R	O
.	O
Smith	O
,	O
Atari	O
Corp	O
.	O
</s>
<s>
The	O
special	O
U	O
:	O
drive	O
contains	O
a	O
virtual	O
DEV	O
directory	B-Application
,	O
inside	O
which	O
one	O
can	O
find	O
device	B-Application
files	I-Application
.	O
</s>
<s>
Windows	O
9x	O
\\devices\	O
Microsoft	B-Device
Windows	I-Device
NT	I-Device
\Device	O
Microsoft	O
The	O
\Device	O
directory	B-Application
is	O
a	O
part	O
of	O
Windows	B-Device
NT	I-Device
object	O
namespace	O
.	O
</s>
<s>
Windows	B-Device
NT	I-Device
Win32	O
Subsystem	O
\\.\	O
Microsoft	O
The	O
\\.\	O
prefix	O
makes	O
supporting	O
APIs	O
access	O
the	O
Win32	O
device	O
namespace	O
instead	O
of	O
the	O
Win32	O
file	B-Operating_System
namespace	O
.	O
</s>
<s>
The	O
Win32	O
device	B-Application
names	I-Application
are	O
symbolic	O
links	O
to	O
device	B-Application
names	I-Application
under	O
Windows	B-Device
NT	I-Device
\Device	O
directory	B-Application
.	O
</s>
