<s>
The	O
Berkeley	B-Operating_System
Software	I-Operating_System
Distribution	I-Operating_System
or	O
Berkeley	O
Standard	O
Distribution	O
(	O
BSD	B-Operating_System
)	O
is	O
a	O
discontinued	O
operating	B-General_Concept
system	I-General_Concept
based	O
on	O
Research	B-Operating_System
Unix	I-Operating_System
,	O
developed	O
and	O
distributed	O
by	O
the	O
Computer	B-Operating_System
Systems	I-Operating_System
Research	I-Operating_System
Group	I-Operating_System
(	O
CSRG	B-Operating_System
)	O
at	O
the	O
University	O
of	O
California	O
,	O
Berkeley	O
.	O
</s>
<s>
The	O
term	O
"	O
BSD	B-Operating_System
"	O
commonly	O
refers	O
to	O
its	O
open-source	B-Application
descendants	O
,	O
including	O
FreeBSD	B-Operating_System
,	O
OpenBSD	B-Operating_System
,	O
NetBSD	B-Device
,	O
and	O
DragonFly	B-Application
BSD	I-Application
.	O
</s>
<s>
BSD	B-Operating_System
was	O
initially	O
called	O
Berkeley	B-Operating_System
Unix	I-Operating_System
because	O
it	O
was	O
based	O
on	O
the	O
source	O
code	O
of	O
the	O
original	O
Unix	B-Application
developed	O
at	O
Bell	O
Labs	O
.	O
</s>
<s>
In	O
the	O
1980s	O
,	O
BSD	B-Operating_System
was	O
widely	O
adopted	O
by	O
workstation	B-Device
vendors	O
in	O
the	O
form	O
of	O
proprietary	B-Application
Unix	B-Application
variants	O
such	O
as	O
DEC	B-Operating_System
Ultrix	I-Operating_System
and	O
Sun	O
Microsystems	O
SunOS	B-Operating_System
due	O
to	O
its	O
permissive	B-License
licensing	I-License
and	O
familiarity	O
to	O
many	O
technology	O
company	O
founders	O
and	O
engineers	O
.	O
</s>
<s>
Although	O
these	O
proprietary	B-Application
BSD	B-Operating_System
derivatives	O
were	O
largely	O
superseded	O
in	O
the	O
1990s	O
by	O
UNIX	B-Application
SVR4	O
and	O
OSF/1	B-Operating_System
,	O
later	O
releases	O
provided	O
the	O
basis	O
for	O
several	O
open-source	B-Application
operating	B-General_Concept
systems	I-General_Concept
including	O
FreeBSD	B-Operating_System
,	O
OpenBSD	B-Operating_System
,	O
NetBSD	B-Device
,	O
DragonFly	B-Application
BSD	I-Application
,	O
Darwin	B-Operating_System
and	O
TrueOS	B-Application
.	O
</s>
<s>
These	O
,	O
in	O
turn	O
,	O
have	O
been	O
used	O
by	O
proprietary	B-Application
operating	B-General_Concept
systems	I-General_Concept
,	O
including	O
Apple	O
's	O
macOS	B-Application
and	O
iOS	B-Application
,	O
which	O
derived	O
from	O
them	O
and	O
Microsoft	B-Application
Windows	I-Application
,	O
which	O
used	O
(	O
at	O
least	O
)	O
part	O
of	O
its	O
TCP/IP	O
code	O
,	O
which	O
was	O
legal	O
.	O
</s>
<s>
Code	O
from	O
FreeBSD	B-Operating_System
was	O
also	O
used	O
to	O
create	O
the	O
operating	B-General_Concept
system	I-General_Concept
for	O
the	O
PlayStation	B-Device
5	I-Device
,	O
PlayStation	B-Operating_System
4	I-Operating_System
,	O
PlayStation	B-Operating_System
3	I-Operating_System
,	O
PlayStation	B-Device
Vita	I-Device
,	O
and	O
Nintendo	B-Application
Switch	I-Application
.	O
</s>
<s>
The	O
earliest	B-Operating_System
distributions	I-Operating_System
of	O
Unix	B-Application
from	O
Bell	O
Labs	O
in	O
the	O
1970s	O
included	O
the	O
source	O
code	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
allowing	O
researchers	O
at	O
universities	O
to	O
modify	O
and	O
extend	O
Unix	B-Application
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
arrived	O
at	O
Berkeley	O
in	O
1974	O
,	O
at	O
the	O
request	O
of	O
computer	O
science	O
professor	O
Bob	O
Fabry	O
who	O
had	O
been	O
on	O
the	O
program	O
committee	O
for	O
the	O
Symposium	O
on	O
Operating	B-General_Concept
Systems	I-General_Concept
Principles	O
where	O
Unix	B-Application
was	O
first	O
presented	O
.	O
</s>
<s>
A	O
PDP-11/45	B-Device
was	O
bought	O
to	O
run	O
the	O
system	O
,	O
but	O
for	O
budgetary	O
reasons	O
,	O
this	O
machine	O
was	O
shared	O
with	O
the	O
mathematics	O
and	O
statistics	O
groups	O
at	O
Berkeley	O
,	O
who	O
used	O
RSTS	B-Operating_System
,	O
so	O
that	O
Unix	B-Application
only	O
ran	O
on	O
the	O
machine	O
eight	O
hours	O
per	O
day	O
(	O
sometimes	O
during	O
the	O
day	O
,	O
sometimes	O
during	O
the	O
night	O
)	O
.	O
</s>
<s>
A	O
larger	O
PDP-11/70	B-Device
was	O
installed	O
at	O
Berkeley	O
the	O
following	O
year	O
,	O
using	O
money	O
from	O
the	O
Ingres	B-Application
database	I-Application
project	O
.	O
</s>
<s>
Understanding	O
BSD	B-Operating_System
requires	O
delving	O
far	O
back	O
into	O
the	O
history	O
of	O
Unix	B-Application
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
first	O
released	O
by	O
AT&T	O
Bell	O
Labs	O
in	O
1969	O
.	O
</s>
<s>
BSD	B-Operating_System
began	O
life	O
as	O
a	O
variant	O
of	O
Unix	B-Application
that	O
programmers	B-Application
at	O
the	O
University	O
of	O
California	O
at	O
Berkeley	O
,	O
initially	O
led	O
by	O
Bill	O
Joy	O
,	O
began	O
developing	O
in	O
the	O
late	O
1970s	O
.	O
</s>
<s>
At	O
first	O
,	O
BSD	B-Operating_System
was	O
not	O
a	O
clone	O
of	O
Unix	B-Application
,	O
or	O
even	O
a	O
substantially	O
different	O
version	O
of	O
it	O
.	O
</s>
<s>
He	O
helped	O
to	O
install	O
Version	B-Operating_System
6	I-Operating_System
Unix	I-Operating_System
and	O
started	O
working	O
on	O
a	O
Pascal	B-Application
implementation	O
for	O
the	O
system	O
.	O
</s>
<s>
Graduate	O
students	O
Chuck	O
Haley	O
and	O
Bill	O
Joy	O
improved	O
Thompson	O
's	O
Pascal	B-Application
and	O
implemented	O
an	O
improved	O
text	O
editor	O
,	O
ex	B-Device
.	O
</s>
<s>
Other	O
universities	O
became	O
interested	O
in	O
the	O
software	O
at	O
Berkeley	O
,	O
and	O
so	O
in	O
1977	O
Joy	O
started	O
compiling	O
the	O
first	O
Berkeley	B-Operating_System
Software	I-Operating_System
Distribution	I-Operating_System
(	O
1BSD	O
)	O
,	O
which	O
was	O
released	O
on	O
March	O
9	O
,	O
1978	O
.	O
</s>
<s>
1BSD	O
was	O
an	O
add-on	O
to	O
Version	B-Operating_System
6	I-Operating_System
Unix	I-Operating_System
rather	O
than	O
a	O
complete	O
operating	B-General_Concept
system	I-General_Concept
in	O
its	O
own	O
right	O
.	O
</s>
<s>
The	O
second	O
Berkeley	B-Operating_System
Software	I-Operating_System
Distribution	I-Operating_System
(	O
2BSD	O
)	O
,	O
released	O
in	O
May	O
1979	O
,	O
included	O
updated	O
versions	O
of	O
the	O
1BSD	O
software	O
as	O
well	O
as	O
two	O
new	O
programs	O
by	O
Joy	O
that	O
persist	O
on	O
Unix	B-Application
systems	I-Application
to	O
this	O
day	O
:	O
the	O
vi	B-Application
text	O
editor	O
(	O
a	O
visual	B-Application
version	O
of	O
ex	B-Device
)	O
and	O
the	O
C	B-Operating_System
shell	I-Operating_System
.	O
</s>
<s>
A	O
VAX	B-Device
computer	O
was	O
installed	O
at	O
Berkeley	O
in	O
1978	O
,	O
but	O
the	O
port	O
of	O
Unix	B-Application
to	O
the	O
VAX	B-Device
architecture	B-General_Concept
,	O
UNIX/32V	B-Operating_System
,	O
did	O
not	O
take	O
advantage	O
of	O
the	O
VAX	B-Device
's	O
virtual	B-Architecture
memory	I-Architecture
capabilities	O
.	O
</s>
<s>
The	O
kernel	B-Operating_System
of	O
32V	B-Operating_System
was	O
largely	O
rewritten	O
to	O
include	O
Berkeley	O
graduate	O
student	O
Özalp	O
Babaoğlu	O
's	O
virtual	B-Architecture
memory	I-Architecture
implementation	O
,	O
and	O
a	O
complete	O
operating	B-General_Concept
system	I-General_Concept
including	O
the	O
new	O
kernel	B-Operating_System
,	O
ports	O
of	O
the	O
2BSD	O
utilities	O
to	O
the	O
VAX	B-Device
,	O
and	O
the	O
utilities	O
from	O
32V	B-Operating_System
was	O
released	O
as	O
3BSD	O
at	O
the	O
end	O
of	O
1979	O
.	O
</s>
<s>
3BSD	O
was	O
also	O
alternatively	O
called	O
Virtual	O
VAX/UNIX	O
or	O
VMUNIX	O
(	O
for	O
Virtual	B-Architecture
Memory	I-Architecture
Unix	B-Application
)	O
,	O
and	O
BSD	B-Operating_System
kernel	B-Operating_System
images	I-Operating_System
were	O
normally	O
called	O
/vmunix	O
until	O
4.4BSD	O
.	O
</s>
<s>
After	O
4.3BSD	O
was	O
released	O
in	O
June	O
1986	O
,	O
it	O
was	O
determined	O
that	O
BSD	B-Operating_System
would	O
move	O
away	O
from	O
the	O
aging	O
VAX	B-Device
platform	O
.	O
</s>
<s>
The	O
Power	O
6/32	O
platform	O
(	O
codenamed	O
"	O
Tahoe	O
"	O
)	O
developed	O
by	O
Computer	O
Consoles	O
Inc	O
.	O
seemed	O
promising	O
at	O
the	O
time	O
,	O
but	O
was	O
abandoned	O
by	O
its	O
developers	B-Application
shortly	O
thereafter	O
.	O
</s>
<s>
Nonetheless	O
,	O
the	O
4.3BSD-Tahoe	O
port	O
(	O
June	O
1988	O
)	O
proved	O
valuable	O
,	O
as	O
it	O
led	O
to	O
a	O
separation	O
of	O
machine-dependent	O
and	O
machine-independent	O
code	O
in	O
BSD	B-Operating_System
which	O
would	O
improve	O
the	O
system	O
's	O
future	O
portability	O
.	O
</s>
<s>
In	O
addition	O
to	O
portability	O
,	O
the	O
CSRG	B-Operating_System
worked	O
on	O
an	O
implementation	O
of	O
the	O
OSI	O
network	B-Architecture
protocol	O
stack	O
,	O
improvements	O
to	O
the	O
kernel	B-Operating_System
virtual	B-Architecture
memory	I-Architecture
system	O
and	O
(	O
with	O
Van	O
Jacobson	O
of	O
LBL	O
)	O
new	O
TCP/IP	O
algorithms	O
to	O
accommodate	O
the	O
growth	O
of	O
the	O
Internet	O
.	O
</s>
<s>
Until	O
then	O
,	O
all	O
versions	O
of	O
BSD	B-Operating_System
used	O
proprietary	B-Application
AT&T	B-Operating_System
Unix	I-Operating_System
code	O
,	O
and	O
were	O
therefore	O
subject	O
to	O
an	O
AT&T	O
software	O
license	O
.	O
</s>
<s>
This	O
led	O
to	O
Networking	O
Release	O
1	O
(	O
Net/1	O
)	O
,	O
which	O
was	O
made	O
available	O
to	O
non-licensees	O
of	O
AT&T	O
code	O
and	O
was	O
freely	B-Application
redistributable	I-Application
under	O
the	O
terms	O
of	O
the	O
BSD	B-Operating_System
license	I-Operating_System
.	O
</s>
<s>
After	O
Net/1	O
,	O
BSD	B-Operating_System
developer	B-Application
Keith	O
Bostic	O
proposed	O
that	O
more	O
non-AT	O
&T	O
sections	O
of	O
the	O
BSD	B-Operating_System
system	O
be	O
released	O
under	O
the	O
same	O
license	O
as	O
Net/1	O
.	O
</s>
<s>
To	O
this	O
end	O
,	O
he	O
started	O
a	O
project	O
to	O
reimplement	O
most	O
of	O
the	O
standard	O
Unix	B-Application
utilities	O
without	O
using	O
the	O
AT&T	O
code	O
.	O
</s>
<s>
Within	O
eighteen	O
months	O
,	O
all	O
of	O
the	O
AT&T	O
utilities	O
had	O
been	O
replaced	O
,	O
and	O
it	O
was	O
determined	O
that	O
only	O
a	O
few	O
AT&T	O
files	O
remained	O
in	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
These	O
files	O
were	O
removed	O
,	O
and	O
the	O
result	O
was	O
the	O
June	O
1991	O
release	O
of	O
Networking	O
Release	O
2	O
(	O
Net/2	O
)	O
,	O
a	O
nearly	O
complete	O
operating	B-General_Concept
system	I-General_Concept
that	O
was	O
freely	O
distributable	O
.	O
</s>
<s>
Net/2	O
was	O
the	O
basis	O
for	O
two	O
separate	O
ports	O
of	O
BSD	B-Operating_System
to	O
the	O
Intel	B-General_Concept
80386	I-General_Concept
architecture	B-General_Concept
:	O
the	O
free	O
386BSD	B-Operating_System
by	O
William	O
Jolitz	O
and	O
the	O
proprietary	B-Application
BSD/386	B-Operating_System
(	O
later	O
renamed	O
BSD/OS	B-Operating_System
)	O
by	O
Berkeley	O
Software	O
Design	O
(	O
BSDi	O
)	O
.	O
</s>
<s>
386BSD	B-Operating_System
itself	O
was	O
short-lived	O
,	O
but	O
became	O
the	O
initial	O
code	O
base	O
of	O
the	O
NetBSD	B-Device
and	O
FreeBSD	B-Operating_System
projects	I-Operating_System
that	O
were	O
started	O
shortly	O
thereafter	O
.	O
</s>
<s>
BSDi	O
soon	O
found	O
itself	O
in	O
legal	O
trouble	O
with	O
T	O
's	O
Unix	B-Application
System	I-Application
Laboratories	O
(	O
USL	O
)	O
subsidiary	O
,	O
then	O
the	O
owners	O
of	O
the	O
System	B-Operating_System
V	I-Operating_System
copyright	O
and	O
the	O
Unix	B-Application
trademark	O
.	O
</s>
<s>
The	O
USL	B-Operating_System
v	I-Operating_System
.	I-Operating_System
BSDi	I-Operating_System
lawsuit	O
was	O
filed	O
in	O
1992	O
and	O
led	O
to	O
an	O
injunction	O
on	O
the	O
distribution	O
of	O
Net/2	O
until	O
the	O
validity	O
of	O
USL	O
's	O
copyright	O
claims	O
on	O
the	O
source	O
could	O
be	O
determined	O
.	O
</s>
<s>
The	O
lawsuit	O
slowed	O
development	O
of	O
the	O
free-software	B-Application
descendants	O
of	O
BSD	B-Operating_System
for	O
nearly	O
two	O
years	O
while	O
their	O
legal	O
status	O
was	O
in	O
question	O
,	O
and	O
as	O
a	O
result	O
systems	O
based	O
on	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
,	O
which	O
did	O
not	O
have	O
such	O
legal	O
ambiguity	O
,	O
gained	O
greater	O
support	O
.	O
</s>
<s>
The	O
final	O
release	O
from	O
Berkeley	O
was	O
1995	O
's	O
4.4BSD-Lite	O
Release	O
2	O
,	O
after	O
which	O
the	O
CSRG	B-Operating_System
was	O
dissolved	O
and	O
development	O
of	O
BSD	B-Operating_System
at	O
Berkeley	O
ceased	O
.	O
</s>
<s>
Since	O
then	O
,	O
several	O
variants	O
based	O
directly	O
or	O
indirectly	O
on	O
4.4BSD-Lite	O
(	O
such	O
as	O
FreeBSD	B-Operating_System
,	O
NetBSD	B-Device
,	O
OpenBSD	B-Operating_System
and	O
DragonFly	B-Application
BSD	I-Application
)	O
have	O
been	O
maintained	O
.	O
</s>
<s>
The	O
permissive	O
nature	O
of	O
the	O
BSD	B-Operating_System
license	I-Operating_System
has	O
allowed	O
many	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
both	O
open-source	B-Application
and	O
proprietary	B-Application
,	O
to	O
incorporate	O
BSD	B-Operating_System
source	O
code	O
.	O
</s>
<s>
For	O
example	O
,	O
Microsoft	B-Application
Windows	I-Application
used	O
BSD	B-Operating_System
code	O
in	O
its	O
implementation	O
of	O
TCP/IP	O
and	O
bundles	O
recompiled	O
versions	O
of	O
BSD	B-Operating_System
's	O
command-line	B-Application
networking	O
tools	O
since	O
Windows	B-Application
2000	I-Application
.	O
</s>
<s>
Darwin	B-Operating_System
,	O
the	O
basis	O
for	O
Apple	O
's	O
macOS	B-Application
and	O
iOS	B-Application
,	O
is	O
based	O
on	O
4.4BSD-Lite2	O
and	O
FreeBSD	B-Operating_System
.	O
</s>
<s>
Various	O
commercial	O
Unix	B-Application
operating	I-Application
systems	I-Application
,	O
such	O
as	O
Solaris	B-Application
,	O
also	O
incorporate	O
BSD	B-Operating_System
code	O
.	O
</s>
<s>
Starting	O
with	O
the	O
8th	O
Edition	O
,	O
versions	O
of	O
Research	B-Operating_System
Unix	I-Operating_System
at	O
Bell	O
Labs	O
had	O
a	O
close	O
relationship	O
to	O
BSD	B-Operating_System
.	O
</s>
<s>
This	O
began	O
when	O
4.1cBSD	O
for	O
the	O
VAX	B-Device
was	O
used	O
as	O
the	O
basis	O
for	O
Research	B-Operating_System
Unix	I-Operating_System
8th	O
Edition	O
.	O
</s>
<s>
The	O
result	O
was	O
that	O
these	O
later	O
versions	O
of	O
Research	B-Operating_System
Unix	I-Operating_System
were	O
closer	O
to	O
BSD	B-Operating_System
than	O
they	O
were	O
to	O
System	B-Operating_System
V	I-Operating_System
.	O
In	O
a	O
Usenet	B-Application
posting	O
from	O
2000	O
,	O
Dennis	O
Ritchie	O
described	O
this	O
relationship	O
between	O
BSD	B-Operating_System
and	O
Research	B-Operating_System
Unix	I-Operating_System
:	O
</s>
<s>
Eric	O
S	O
.	O
Raymond	O
summarizes	O
the	O
longstanding	O
relationship	O
between	O
System	B-Operating_System
V	I-Operating_System
and	O
BSD	B-Operating_System
,	O
stating	O
,	O
"	O
The	O
divide	O
was	O
roughly	O
between	O
longhairs	O
and	O
shorthairs	O
;	O
programmers	B-Application
and	O
technical	O
people	O
tended	O
to	O
line	O
up	O
with	O
Berkeley	O
and	O
BSD	B-Operating_System
,	O
more	O
business-oriented	O
types	O
with	O
AT&T	O
and	O
System	O
V.	O
"	O
</s>
<s>
In	O
1989	O
,	O
David	O
A	O
.	O
Curry	O
wrote	O
about	O
the	O
differences	O
between	O
BSD	B-Operating_System
and	O
System	B-Operating_System
V	I-Operating_System
.	O
He	O
characterized	O
System	B-Operating_System
V	I-Operating_System
as	O
being	O
often	O
regarded	O
as	O
the	O
"	O
standard	O
Unix.	O
"	O
</s>
<s>
However	O
,	O
he	O
described	O
BSD	B-Operating_System
as	O
more	O
popular	O
among	O
university	O
and	O
government	O
computer	O
centers	O
,	O
due	O
to	O
its	O
advanced	O
features	O
and	O
performance	O
:	O
</s>
<s>
Berkeley	O
's	O
Unix	B-Application
was	O
the	O
first	O
Unix	B-Application
to	O
include	O
libraries	O
supporting	O
the	O
Internet	B-Protocol
Protocol	I-Protocol
stacks	O
:	O
Berkeley	B-Protocol
sockets	I-Protocol
.	O
</s>
<s>
A	O
Unix	B-Application
implementation	O
of	O
IP	O
's	O
predecessor	O
,	O
the	O
ARPAnet	O
's	O
NCP	B-Protocol
,	O
with	O
FTP	B-Protocol
and	O
Telnet	B-Protocol
clients	O
,	O
had	O
been	O
produced	O
at	O
the	O
University	O
of	O
Illinois	O
in	O
1975	O
,	O
and	O
was	O
available	O
at	O
Berkeley	O
.	O
</s>
<s>
However	O
,	O
the	O
memory	O
scarcity	O
on	O
the	O
PDP-11	B-Device
forced	O
a	O
complicated	O
design	O
and	O
performance	O
problems	O
.	O
</s>
<s>
By	O
integrating	O
sockets	O
with	O
the	O
Unix	B-Application
operating	I-Application
system	I-Application
's	O
file	B-Application
descriptors	I-Application
,	O
it	O
became	O
almost	O
as	O
easy	O
to	O
read	O
and	O
write	O
data	O
across	O
a	O
network	B-Architecture
as	O
it	O
was	O
to	O
access	O
a	O
disk	O
.	O
</s>
<s>
The	O
AT&T	O
laboratory	O
eventually	O
released	O
their	O
own	O
STREAMS	B-Operating_System
library	O
,	O
which	O
incorporated	O
much	O
of	O
the	O
same	O
functionality	O
in	O
a	O
software	O
stack	O
with	O
a	O
different	O
architecture	B-General_Concept
,	O
but	O
the	O
wide	O
distribution	O
of	O
the	O
existing	O
sockets	O
library	O
reduced	O
the	O
impact	O
of	O
the	O
new	O
API	B-Application
.	O
</s>
<s>
Early	O
versions	O
of	O
BSD	B-Operating_System
were	O
used	O
to	O
form	O
Sun	O
Microsystems	O
 '	O
SunOS	B-Operating_System
,	O
founding	O
the	O
first	O
wave	O
of	O
popular	O
Unix	B-Device
workstations	I-Device
.	O
</s>
<s>
Some	O
BSD	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
can	O
run	O
native	O
software	O
of	O
several	O
other	O
operating	B-General_Concept
systems	I-General_Concept
on	O
the	O
same	O
architecture	B-General_Concept
,	O
using	O
a	O
binary	O
compatibility	B-General_Concept
layer	I-General_Concept
.	O
</s>
<s>
This	O
is	O
much	O
simpler	O
and	O
faster	O
than	O
emulation	B-Application
;	O
for	O
example	O
,	O
it	O
allows	O
applications	O
intended	O
for	O
Linux	B-Application
to	O
be	O
run	O
at	O
effectively	O
full	O
speed	O
.	O
</s>
<s>
This	O
makes	O
BSDs	B-Operating_System
not	O
only	O
suitable	O
for	O
server	O
environments	O
,	O
but	O
also	O
for	O
workstation	B-Device
ones	O
,	O
given	O
the	O
increasing	O
availability	O
of	O
commercial	O
or	O
closed-source	B-Application
software	I-Application
for	O
Linux	B-Application
only	O
.	O
</s>
<s>
This	O
also	O
allows	O
administrators	O
to	O
migrate	O
legacy	O
commercial	O
applications	O
,	O
which	O
may	O
have	O
only	O
supported	O
commercial	O
Unix	B-Application
variants	O
,	O
to	O
a	O
more	O
modern	O
operating	B-General_Concept
system	I-General_Concept
,	O
retaining	O
the	O
functionality	O
of	O
such	O
applications	O
until	O
they	O
can	O
be	O
replaced	O
by	O
a	O
better	O
alternative	O
.	O
</s>
<s>
Current	O
BSD	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
variants	O
support	O
many	O
of	O
the	O
common	O
IEEE	O
,	O
ANSI	O
,	O
ISO	O
,	O
and	O
POSIX	O
standards	O
,	O
while	O
retaining	O
most	O
of	O
the	O
traditional	O
BSD	B-Operating_System
behavior	O
.	O
</s>
<s>
Like	O
AT&T	B-Operating_System
Unix	I-Operating_System
,	O
the	O
BSD	B-Operating_System
kernel	B-Operating_System
is	O
monolithic	B-Operating_System
,	O
meaning	O
that	O
device	O
drivers	O
in	O
the	O
kernel	B-Operating_System
run	O
in	O
privileged	B-Operating_System
mode	I-Operating_System
,	O
as	O
part	O
of	O
the	O
core	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Several	O
operating	B-General_Concept
systems	I-General_Concept
are	O
based	O
on	O
BSD	B-Operating_System
,	O
including	O
FreeBSD	B-Operating_System
,	O
OpenBSD	B-Operating_System
,	O
NetBSD	B-Device
,	O
MidnightBSD	B-Application
,	O
MirOS	B-Application
BSD	I-Application
,	O
GhostBSD	B-Application
,	O
Darwin	B-Operating_System
and	O
DragonFly	B-Application
BSD	I-Application
.	O
</s>
<s>
Both	O
NetBSD	B-Device
and	O
FreeBSD	B-Operating_System
were	O
created	O
in	O
1993	O
.	O
</s>
<s>
They	O
were	O
initially	O
derived	O
from	O
386BSD	B-Operating_System
(	O
also	O
known	O
as	O
"	O
Jolix	B-Operating_System
"	O
)	O
,	O
and	O
merged	O
the	O
4.4BSD-Lite	O
source	O
code	O
in	O
1994	O
.	O
</s>
<s>
OpenBSD	B-Operating_System
was	O
forked	B-Application
from	O
NetBSD	B-Device
in	O
1995	O
,	O
and	O
DragonFly	B-Application
BSD	I-Application
was	O
forked	B-Application
from	O
FreeBSD	B-Operating_System
in	O
2003	O
.	O
</s>
<s>
BSD	B-Operating_System
was	O
also	O
used	O
as	O
the	O
basis	O
for	O
several	O
proprietary	B-Application
versions	O
of	O
Unix	B-Application
,	O
such	O
as	O
Sun	O
's	O
SunOS	B-Operating_System
,	O
Sequent	O
's	O
DYNIX	B-Library
,	O
NeXT	O
's	O
NeXTSTEP	B-Application
,	O
DEC	O
's	O
Ultrix	B-Operating_System
and	O
OSF/1	B-Operating_System
AXP	I-Operating_System
(	O
now	O
Tru64	B-Operating_System
UNIX	I-Operating_System
)	O
.	O
</s>
<s>
NeXTSTEP	B-Application
later	O
became	O
the	O
foundation	O
for	O
Apple	O
Inc.	O
'	O
s	O
macOS	B-Application
.	O
</s>
