<s>
Unix	B-Application
(	O
;	O
trademarked	O
as	O
UNIX	B-Application
)	O
is	O
a	O
family	O
of	O
multitasking	B-Operating_System
,	O
multiuser	B-Operating_System
computer	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
that	O
derive	O
from	O
the	O
original	O
AT&T	B-Operating_System
Unix	I-Operating_System
,	O
whose	O
development	O
started	O
in	O
1969	O
at	O
the	O
Bell	O
Labs	O
research	O
center	O
by	O
Ken	O
Thompson	O
,	O
Dennis	O
Ritchie	O
,	O
and	O
others	O
.	O
</s>
<s>
Initially	O
intended	O
for	O
use	O
inside	O
the	O
Bell	O
System	O
,	O
AT&T	O
licensed	O
Unix	B-Application
to	O
outside	O
parties	O
in	O
the	O
late	O
1970s	O
,	O
leading	O
to	O
a	O
variety	O
of	O
both	O
academic	O
and	O
commercial	O
Unix	B-Application
variants	O
from	O
vendors	O
including	O
University	O
of	O
California	O
,	O
Berkeley	O
(	O
BSD	B-Operating_System
)	O
,	O
Microsoft	O
(	O
Xenix	B-Application
)	O
,	O
Sun	O
Microsystems	O
(	O
SunOS/Solaris	O
)	O
,	O
HP/HPE	O
(	O
HP-UX	B-Application
)	O
,	O
and	O
IBM	O
(	O
AIX	B-Application
)	O
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
,	O
AT&T	O
sold	O
its	O
rights	O
in	O
Unix	B-Application
to	O
Novell	O
,	O
which	O
then	O
sold	O
the	O
UNIX	B-Application
trademark	O
to	O
The	B-Application
Open	I-Application
Group	I-Application
,	O
an	O
industry	O
consortium	O
founded	O
in	O
1996	O
.	O
</s>
<s>
The	B-Application
Open	I-Application
Group	I-Application
allows	O
the	O
use	O
of	O
the	O
mark	O
for	O
certified	O
operating	B-General_Concept
systems	I-General_Concept
that	O
comply	O
with	O
the	O
Single	O
UNIX	B-Application
Specification	O
(	O
SUS	O
)	O
.	O
</s>
<s>
Unix	B-Operating_System
systems	I-Operating_System
are	O
characterized	O
by	O
a	O
modular	B-Architecture
design	O
that	O
is	O
sometimes	O
called	O
the	O
"	O
Unix	B-Operating_System
philosophy	I-Operating_System
"	O
.	O
</s>
<s>
According	O
to	O
this	O
philosophy	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
should	O
provide	O
a	O
set	O
of	O
simple	O
tools	O
,	O
each	O
of	O
which	O
performs	O
a	O
limited	O
,	O
well-defined	O
function	O
.	O
</s>
<s>
A	O
unified	O
and	O
inode-based	O
filesystem	B-Application
(	O
the	O
Unix	B-Application
filesystem	I-Application
)	O
and	O
an	O
inter-process	B-Operating_System
communication	I-Operating_System
mechanism	O
known	O
as	O
"	O
pipes	B-Operating_System
"	O
serve	O
as	O
the	O
main	O
means	O
of	O
communication	O
,	O
and	O
a	O
shell	B-Language
scripting	I-Language
and	O
command	O
language	O
(	O
the	O
Unix	B-Application
shell	I-Application
)	O
is	O
used	O
to	O
combine	O
the	O
tools	O
to	O
perform	O
complex	O
workflows	O
.	O
</s>
<s>
Unix	B-Application
distinguishes	O
itself	O
from	O
its	O
predecessors	O
as	O
the	O
first	O
portable	B-Architecture
operating	B-General_Concept
system	I-General_Concept
:	O
almost	O
the	O
entire	O
operating	B-General_Concept
system	I-General_Concept
is	O
written	O
in	O
the	O
C	B-Language
programming	I-Language
language	I-Language
,	O
which	O
allows	O
Unix	B-Application
to	O
operate	O
on	O
numerous	O
platforms	O
.	O
</s>
<s>
Unix	B-Application
was	O
originally	O
meant	O
to	O
be	O
a	O
convenient	O
platform	O
for	O
programmers	O
developing	O
software	O
to	O
be	O
run	O
on	O
it	O
and	O
on	O
other	O
systems	O
,	O
rather	O
than	O
for	O
non-programmers	O
.	O
</s>
<s>
The	O
system	O
grew	O
larger	O
as	O
the	O
operating	B-General_Concept
system	I-General_Concept
started	O
spreading	O
in	O
academic	O
circles	O
,	O
and	O
as	O
users	O
added	O
their	O
own	O
tools	O
to	O
the	O
system	O
and	O
shared	O
them	O
with	O
colleagues	O
.	O
</s>
<s>
At	O
first	O
,	O
Unix	B-Application
was	O
not	O
designed	O
to	O
be	O
portable	B-Architecture
or	O
for	O
multi-tasking	B-Operating_System
.	O
</s>
<s>
Later	O
,	O
Unix	B-Application
gradually	O
gained	O
portability	B-Architecture
,	O
multi-tasking	B-Operating_System
and	O
multi-user	B-Operating_System
capabilities	O
in	O
a	O
time-sharing	B-General_Concept
configuration	O
.	O
</s>
<s>
Unix	B-Operating_System
systems	I-Operating_System
are	O
characterized	O
by	O
various	O
concepts	O
:	O
the	O
use	O
of	O
plain	O
text	O
for	O
storing	O
data	O
;	O
a	O
hierarchical	B-Application
file	I-Application
system	I-Application
;	O
treating	O
devices	O
and	O
certain	O
types	O
of	O
inter-process	B-Operating_System
communication	I-Operating_System
(	O
IPC	O
)	O
as	O
files	O
;	O
and	O
the	O
use	O
of	O
a	O
large	O
number	O
of	O
software	B-Application
tools	I-Application
,	O
small	O
programs	O
that	O
can	O
be	O
strung	O
together	O
through	O
a	O
command-line	B-Application
interpreter	O
using	O
pipes	B-Operating_System
,	O
as	O
opposed	O
to	O
using	O
a	O
single	O
monolithic	B-Operating_System
program	O
that	O
includes	O
all	O
of	O
the	O
same	O
functionality	O
.	O
</s>
<s>
These	O
concepts	O
are	O
collectively	O
known	O
as	O
the	O
"	O
Unix	B-Operating_System
philosophy	I-Operating_System
"	O
.	O
</s>
<s>
Brian	O
Kernighan	O
and	O
Rob	O
Pike	O
summarize	O
this	O
in	O
The	O
Unix	B-Application
Programming	O
Environment	O
as	O
"	O
the	O
idea	O
that	O
the	O
power	O
of	O
a	O
system	O
comes	O
more	O
from	O
the	O
relationships	O
among	O
programs	O
than	O
from	O
the	O
programs	O
themselves	O
"	O
.	O
</s>
<s>
By	O
the	O
early	O
1980s	O
,	O
users	O
began	O
seeing	O
Unix	B-Application
as	O
a	O
potential	O
universal	O
operating	B-General_Concept
system	I-General_Concept
,	O
suitable	O
for	O
computers	O
of	O
all	O
sizes	O
.	O
</s>
<s>
The	O
Unix	B-Application
environment	O
and	O
the	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
program	O
model	O
were	O
essential	O
elements	O
in	O
the	O
development	O
of	O
the	O
Internet	O
and	O
the	O
reshaping	O
of	O
computing	O
as	O
centered	O
in	O
networks	B-Architecture
rather	O
than	O
in	O
individual	O
computers	O
.	O
</s>
<s>
Both	O
Unix	B-Application
and	O
the	O
C	B-Language
programming	I-Language
language	I-Language
were	O
developed	O
by	O
AT&T	O
and	O
distributed	O
to	O
government	O
and	O
academic	O
institutions	O
,	O
which	O
led	O
to	O
both	O
being	O
ported	O
to	O
a	O
wider	O
variety	O
of	O
machine	O
families	O
than	O
any	O
other	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
Unix	B-Application
operating	I-Application
system	I-Application
consists	O
of	O
many	O
libraries	O
and	O
utilities	O
along	O
with	O
the	O
master	B-Application
control	I-Application
program	I-Application
,	O
the	O
kernel	B-Operating_System
.	O
</s>
<s>
The	O
kernel	B-Operating_System
provides	O
services	O
to	O
start	O
and	O
stop	O
programs	O
,	O
handles	O
the	O
file	B-Application
system	I-Application
and	O
other	O
common	O
"	O
low-level	O
"	O
tasks	O
that	O
most	O
programs	O
share	O
,	O
and	O
schedules	O
access	O
to	O
avoid	O
conflicts	O
when	O
programs	O
try	O
to	O
access	O
the	O
same	O
resource	O
or	O
device	O
simultaneously	O
.	O
</s>
<s>
To	O
mediate	O
such	O
access	O
,	O
the	O
kernel	B-Operating_System
has	O
special	O
rights	O
,	O
reflected	O
in	O
the	O
distinction	O
of	O
kernel	B-Operating_System
space	I-Operating_System
from	O
user	B-Operating_System
space	I-Operating_System
,	O
the	O
latter	O
being	O
a	O
priority	O
realm	O
where	O
most	O
application	O
programs	O
operate	O
.	O
</s>
<s>
The	O
origins	O
of	O
Unix	B-Operating_System
date	I-Operating_System
back	O
to	O
the	O
mid-1960s	O
when	O
the	O
Massachusetts	O
Institute	O
of	O
Technology	O
,	O
Bell	O
Labs	O
,	O
and	O
General	O
Electric	O
were	O
developing	O
Multics	B-Application
,	O
a	O
time-sharing	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
for	O
the	O
GE-645	B-Device
mainframe	O
computer	O
.	O
</s>
<s>
Multics	B-Application
featured	O
several	O
innovations	O
,	O
but	O
also	O
presented	O
severe	O
problems	O
.	O
</s>
<s>
Frustrated	O
by	O
the	O
size	O
and	O
complexity	O
of	O
Multics	B-Application
,	O
but	O
not	O
by	O
its	O
goals	O
,	O
individual	O
researchers	O
at	O
Bell	O
Labs	O
started	O
withdrawing	O
from	O
the	O
project	O
.	O
</s>
<s>
This	O
new	O
operating	B-General_Concept
system	I-General_Concept
was	O
initially	O
without	O
organizational	O
backing	O
,	O
and	O
also	O
without	O
a	O
name	O
.	O
</s>
<s>
The	O
new	O
operating	B-General_Concept
system	I-General_Concept
was	O
a	O
single-tasking	O
system	O
.	O
</s>
<s>
In	O
1970	O
,	O
the	O
group	O
coined	O
the	O
name	O
Unics	O
for	O
Uniplexed	O
Information	O
and	O
Computing	O
Service	O
as	O
a	O
pun	O
on	O
Multics	B-Application
,	O
which	O
stood	O
for	O
Multiplexed	O
Information	O
and	O
Computer	O
Services	O
.	O
</s>
<s>
Brian	O
Kernighan	O
takes	O
credit	O
for	O
the	O
idea	O
,	O
but	O
adds	O
that	O
"	O
no	O
one	O
can	O
remember	O
"	O
the	O
origin	O
of	O
the	O
final	O
spelling	O
Unix	B-Application
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
was	O
originally	O
written	O
in	O
assembly	B-Language
language	I-Language
,	O
but	O
in	O
1973	O
,	O
Version	B-Operating_System
4	I-Operating_System
Unix	I-Operating_System
was	O
rewritten	O
in	O
C	B-Language
.	O
Version	B-Operating_System
4	I-Operating_System
Unix	I-Operating_System
,	O
however	O
,	O
still	O
had	O
many	O
PDP-11	B-Device
dependent	O
codes	O
,	O
and	O
was	O
not	O
suitable	O
for	O
porting	O
.	O
</s>
<s>
The	O
first	O
port	O
to	O
another	O
platform	O
was	O
made	O
five	O
years	O
later	O
(	O
1978	O
)	O
for	O
the	O
Interdata	B-Device
8/32	I-Device
.	O
</s>
<s>
Bell	O
Labs	O
produced	O
several	O
versions	O
of	O
Unix	B-Application
that	O
are	O
collectively	O
referred	O
to	O
as	O
Research	B-Operating_System
Unix	I-Operating_System
.	O
</s>
<s>
In	O
1975	O
,	O
the	O
first	O
source	O
license	O
for	O
UNIX	B-Application
was	O
sold	O
to	O
Donald	O
B	O
.	O
Gillies	O
at	O
the	O
University	O
of	O
Illinois	O
Urbana	O
–	O
Champaign	O
Department	O
of	O
Computer	O
Science	O
(	O
UIUC	O
)	O
.	O
</s>
<s>
UIUC	O
graduate	O
student	O
Greg	O
Chesson	O
,	O
who	O
had	O
worked	O
on	O
the	O
Unix	B-Application
kernel	B-Operating_System
at	O
Bell	O
Labs	O
,	O
was	O
instrumental	O
in	O
negotiating	O
the	O
terms	O
of	O
the	O
license	O
.	O
</s>
<s>
During	O
the	O
late	O
1970s	O
and	O
early	O
1980s	O
,	O
the	O
influence	O
of	O
Unix	B-Application
in	O
academic	O
circles	O
led	O
to	O
large-scale	O
adoption	O
of	O
Unix	B-Application
(	O
BSD	B-Operating_System
and	O
System	B-Operating_System
V	I-Operating_System
)	O
by	O
commercial	O
startups	O
,	O
which	O
in	O
turn	O
led	O
to	O
Unix	B-Application
fragmenting	O
into	O
multiple	O
,	O
similar	O
but	O
often	O
slightly	O
mutually-incompatible	O
systems	O
including	O
DYNIX	B-Library
,	O
HP-UX	B-Application
,	O
SunOS/Solaris	O
,	O
AIX	B-Application
,	O
and	O
Xenix	B-Application
.	O
</s>
<s>
In	O
the	O
late	O
1980s	O
,	O
AT&T	B-Operating_System
Unix	I-Operating_System
System	O
Laboratories	O
and	O
Sun	O
Microsystems	O
developed	O
SystemV	B-Operating_System
Release4	O
(	O
SVR4	O
)	O
,	O
which	O
was	O
subsequently	O
adopted	O
by	O
many	O
commercial	O
Unix	B-Application
vendors	O
.	O
</s>
<s>
In	O
the	O
1990s	O
,	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
systems	I-Operating_System
grew	O
in	O
popularity	O
and	O
became	O
the	O
operating	B-General_Concept
system	I-General_Concept
of	O
choice	O
for	O
over	O
90%	O
of	O
the	O
world	O
's	O
top	O
500	O
fastest	O
supercomputers	O
,	O
as	O
BSD	B-Operating_System
and	O
Linux	B-Application
distributions	I-Application
were	O
developed	O
through	O
collaboration	O
by	O
a	O
worldwide	O
network	O
of	O
programmers	O
.	O
</s>
<s>
In	O
2000	O
,	O
Apple	O
released	O
Darwin	B-Operating_System
,	O
also	O
a	O
Unix	B-Application
system	I-Application
,	O
which	O
became	O
the	O
core	O
of	O
the	O
Mac	B-Application
OS	I-Application
X	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
,	O
later	O
renamed	O
macOS	B-Application
.	O
</s>
<s>
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
are	O
widely	O
used	O
in	O
modern	O
servers	B-Application
,	O
workstations	B-Device
,	O
and	O
mobile	B-Application
devices	I-Application
.	O
</s>
<s>
In	O
the	O
late	O
1980s	O
,	O
an	O
open	O
operating	B-General_Concept
system	I-General_Concept
standardization	O
effort	O
now	O
known	O
as	O
POSIX	O
provided	O
a	O
common	O
baseline	O
for	O
all	O
operating	B-General_Concept
systems	I-General_Concept
;	O
IEEE	O
based	O
POSIX	O
around	O
the	O
common	O
structure	O
of	O
the	O
major	O
competing	O
variants	O
of	O
the	O
Unix	B-Application
system	I-Application
,	O
publishing	O
the	O
first	O
POSIX	O
standard	O
in	O
1988	O
.	O
</s>
<s>
In	O
the	O
early	O
1990s	O
,	O
a	O
separate	O
but	O
very	O
similar	O
effort	O
was	O
started	O
by	O
an	O
industry	O
consortium	O
,	O
the	O
Common	B-Operating_System
Open	I-Operating_System
Software	I-Operating_System
Environment	I-Operating_System
(	O
COSE	O
)	O
initiative	O
,	O
which	O
eventually	O
became	O
the	O
Single	O
UNIX	B-Application
Specification	O
(	O
SUS	O
)	O
administered	O
by	O
The	B-Application
Open	I-Application
Group	I-Application
.	O
</s>
<s>
Starting	O
in	O
1998	O
,	O
the	B-Application
Open	I-Application
Group	I-Application
and	O
IEEE	O
started	O
the	O
Austin	O
Group	O
,	O
to	O
provide	O
a	O
common	O
definition	O
of	O
POSIX	O
and	O
the	O
Single	O
UNIX	B-Application
Specification	O
,	O
which	O
,	O
by	O
2008	O
,	O
had	O
become	O
the	B-Application
Open	I-Application
Group	I-Application
Base	O
Specification	O
.	O
</s>
<s>
In	O
1999	O
,	O
in	O
an	O
effort	O
towards	O
compatibility	O
,	O
several	O
Unix	B-Application
system	I-Application
vendors	O
agreed	O
on	O
SVR4	O
's	O
Executable	O
and	O
Linkable	O
Format	O
(	O
ELF	O
)	O
as	O
the	O
standard	O
for	O
binary	O
and	O
object	O
code	O
files	O
.	O
</s>
<s>
The	O
common	O
format	O
allows	O
substantial	O
binary	O
compatibility	O
among	O
different	O
Unix	B-Operating_System
systems	I-Operating_System
operating	O
on	O
the	O
same	O
CPU	O
architecture	O
.	O
</s>
<s>
The	O
Filesystem	B-Application
Hierarchy	I-Application
Standard	I-Application
was	O
created	O
to	O
provide	O
a	O
reference	O
directory	O
layout	O
for	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
;	O
it	O
has	O
mainly	O
been	O
used	O
in	O
Linux	B-Operating_System
.	O
</s>
<s>
The	O
Unix	B-Application
system	I-Application
is	O
composed	O
of	O
several	O
components	O
that	O
were	O
originally	O
packaged	O
together	O
.	O
</s>
<s>
By	O
including	O
the	O
development	O
environment	O
,	O
libraries	O
,	O
documents	O
and	O
the	O
portable	B-Architecture
,	O
modifiable	O
source	O
code	O
for	O
all	O
of	O
these	O
components	O
,	O
in	O
addition	O
to	O
the	O
kernel	B-Operating_System
of	O
an	O
operating	B-General_Concept
system	I-General_Concept
,	O
Unix	B-Application
was	O
a	O
self-contained	O
software	O
system	O
.	O
</s>
<s>
The	O
inclusion	O
of	O
these	O
components	O
did	O
not	O
make	B-Application
the	O
system	O
large	O
the	O
original	O
V7	B-Operating_System
UNIX	I-Operating_System
distribution	O
,	O
consisting	O
of	O
copies	O
of	O
all	O
of	O
the	O
compiled	B-Language
binaries	O
plus	O
all	O
of	O
the	O
source	O
code	O
and	O
documentation	O
occupied	O
less	O
than	O
10MB	O
and	O
arrived	O
on	O
a	O
single	O
nine-track	O
magnetic	B-Architecture
tape	I-Architecture
,	O
earning	O
its	O
reputation	O
as	O
a	O
portable	B-Architecture
system	O
.	O
</s>
<s>
The	O
names	O
and	O
filesystem	B-Application
locations	O
of	O
the	O
Unix	B-Application
components	O
have	O
changed	O
substantially	O
across	O
the	O
history	O
of	O
the	O
system	O
.	O
</s>
<s>
Kernel	B-Operating_System
source	O
code	O
in	O
/usr/sys	O
,	O
composed	O
of	O
several	O
sub-components	O
:	O
</s>
<s>
sys	O
operating	B-General_Concept
system	I-General_Concept
"	O
kernel	B-Operating_System
"	O
,	O
handling	O
memory	O
management	O
,	O
process	O
scheduling	O
,	O
system	B-Operating_System
calls	I-Operating_System
,	O
etc	O
.	O
</s>
<s>
Development	O
environment	O
early	O
versions	O
of	O
Unix	B-Application
contained	O
a	O
development	O
environment	O
sufficient	O
to	O
recreate	O
the	O
entire	O
system	O
from	O
source	O
code	O
:	O
</s>
<s>
libc	B-Language
,	O
the	O
system	O
library	O
with	O
C	B-Language
run-time	I-Language
support	O
,	O
was	O
the	O
primary	O
library	O
,	O
but	O
there	O
have	O
always	O
been	O
additional	O
libraries	O
for	O
things	O
such	O
as	O
mathematical	O
functions	O
(	O
libm	O
)	O
or	O
database	O
access	O
.	O
</s>
<s>
V7	B-Operating_System
Unix	I-Operating_System
introduced	O
the	O
first	O
version	O
of	O
the	O
modern	O
"	O
Standard	O
I/O	O
"	O
library	O
stdio	O
as	O
part	O
of	O
the	O
system	O
library	O
.	O
</s>
<s>
Other	O
languages	O
V7	B-Operating_System
Unix	I-Operating_System
contained	O
a	O
Fortran-77	O
compiler	B-Language
,	O
a	O
programmable	O
arbitrary-precision	O
calculator	O
(	O
bc	O
,	O
dc	O
)	O
,	O
and	O
the	O
awk	B-Application
scripting	O
language	O
;	O
later	O
versions	O
and	O
implementations	O
contain	O
many	O
other	O
language	B-Language
compilers	I-Language
and	O
toolsets	B-Application
.	O
</s>
<s>
Early	O
BSD	B-Operating_System
releases	O
included	O
Pascal	B-Application
tools	O
,	O
and	O
many	O
modern	O
Unix	B-Operating_System
systems	I-Operating_System
also	O
include	O
the	O
GNU	B-Application
Compiler	I-Application
Collection	I-Application
as	O
well	O
as	O
or	O
instead	O
of	O
a	O
proprietary	B-Application
compiler	B-Language
system	O
.	O
</s>
<s>
Other	O
tools	O
including	O
an	O
object-code	O
archive	O
manager	O
(	O
ar	B-Application
)	O
,	O
symbol-table	O
lister	O
(	O
nm	O
)	O
,	O
compiler-development	O
tools	O
(	O
e.g.	O
</s>
<s>
lex	B-General_Concept
&	O
yacc	B-Application
)	O
,	O
and	O
debugging	O
tools	O
.	O
</s>
<s>
Commands	O
Unix	B-Application
makes	O
little	O
distinction	O
between	O
commands	O
(	O
user-level	B-Operating_System
programs	O
)	O
for	O
system	O
operation	O
and	O
maintenance	O
(	O
e.g.	O
</s>
<s>
cron	B-General_Concept
)	O
,	O
commands	O
of	O
general	O
utility	O
(	O
e.g.	O
</s>
<s>
grep	B-Application
)	O
,	O
and	O
more	O
general-purpose	O
applications	O
such	O
as	O
the	O
text	O
formatting	O
and	O
typesetting	O
package	O
.	O
</s>
<s>
sh	B-Device
the	O
"	O
shell	B-Operating_System
"	O
programmable	O
command-line	B-Application
interpreter	O
,	O
the	O
primary	O
user	O
interface	O
on	O
Unix	B-Application
before	O
window	O
systems	O
appeared	O
,	O
and	O
even	O
afterward	O
(	O
within	O
a	O
"	O
command	B-Application
window	I-Application
"	O
)	O
.	O
</s>
<s>
Utilities	O
the	O
core	O
toolkit	O
of	O
the	O
Unix	B-Application
command	I-Application
set	O
,	O
including	O
cp	B-Application
,	O
ls	B-Application
,	O
grep	B-Application
,	O
find	B-Application
and	O
many	O
others	O
.	O
</s>
<s>
System	O
utilities	O
administrative	O
tools	O
such	O
as	O
mkfs	B-Device
,	O
fsck	B-Device
,	O
and	O
many	O
others	O
.	O
</s>
<s>
Document	O
formatting	O
Unix	B-Operating_System
systems	I-Operating_System
were	O
used	O
from	O
the	O
outset	O
for	O
document	O
preparation	O
and	O
typesetting	O
systems	O
,	O
and	O
included	O
many	O
related	O
programs	O
such	O
as	O
nroff	B-Device
,	O
troff	B-Language
,	O
tbl	B-Application
,	O
eqn	B-Application
,	O
refer	B-Application
,	O
and	O
pic	B-Language
.	O
</s>
<s>
Some	O
modern	O
Unix	B-Operating_System
systems	I-Operating_System
also	O
include	O
packages	O
such	O
as	O
TeX	B-Application
and	O
Ghostscript	B-Language
.	O
</s>
<s>
Modern	O
Unix	B-Operating_System
systems	I-Operating_System
also	O
generally	O
include	O
X11	B-Operating_System
as	O
a	O
standard	O
windowing	O
system	O
and	O
GUI	B-Application
,	O
and	O
many	O
support	O
OpenGL	B-Application
.	O
</s>
<s>
Communications	O
early	O
Unix	B-Operating_System
systems	I-Operating_System
contained	O
no	O
inter-system	O
communication	O
,	O
but	O
did	O
include	O
the	O
inter-user	O
communication	O
programs	O
mail	O
and	O
write	O
.	O
</s>
<s>
V7	O
introduced	O
the	O
early	O
inter-system	O
communication	O
system	O
UUCP	B-Protocol
,	O
and	O
systems	O
beginning	O
with	O
BSD	B-Operating_System
release	O
4.1c	O
included	O
TCP/IP	B-Protocol
utilities	O
.	O
</s>
<s>
Documentation	O
Unix	B-Application
was	O
one	O
of	O
the	O
first	O
operating	B-General_Concept
systems	I-General_Concept
to	O
include	O
all	O
of	O
its	O
documentation	O
online	O
in	O
machine-readable	O
form	O
.	O
</s>
<s>
man	B-Protocol
manual	B-Protocol
pages	I-Protocol
for	O
each	O
command	O
,	O
library	O
component	O
,	O
system	B-Operating_System
call	I-Operating_System
,	O
header	O
file	O
,	O
etc	O
.	O
</s>
<s>
The	O
Unix	B-Application
system	I-Application
had	O
a	O
significant	O
impact	O
on	O
other	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
Unix	B-Application
was	O
originally	O
written	O
in	O
assembly	B-Language
language	I-Language
,	O
but	O
was	O
soon	O
rewritten	O
in	O
C	B-Language
,	O
a	O
high-level	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
Although	O
this	O
followed	O
the	O
lead	O
of	O
CTSS	B-Operating_System
,	O
Multics	B-Application
and	O
Burroughs	B-Application
MCP	I-Application
,	O
it	O
was	O
Unix	B-Application
that	O
popularized	O
the	O
idea	O
.	O
</s>
<s>
Unix	B-Application
had	O
a	O
drastically	O
simplified	O
file	O
model	O
compared	O
to	O
many	O
contemporary	O
operating	B-General_Concept
systems	I-General_Concept
:	O
treating	O
all	O
kinds	O
of	O
files	O
as	O
simple	O
byte	O
arrays	O
.	O
</s>
<s>
The	O
file	B-Application
system	I-Application
hierarchy	O
contained	O
machine	O
services	O
and	O
devices	O
(	O
such	O
as	O
printers	O
,	O
terminals	B-General_Concept
,	O
or	O
disk	B-Device
drives	I-Device
)	O
,	O
providing	O
a	O
uniform	O
interface	O
,	O
but	O
at	O
the	O
expense	O
of	O
occasionally	O
requiring	O
additional	O
mechanisms	O
such	O
as	O
ioctl	B-Operating_System
and	O
mode	O
flags	O
to	O
access	O
features	O
of	O
the	O
hardware	O
that	O
did	O
not	O
fit	O
the	O
simple	O
"	O
stream	O
of	O
bytes	O
"	O
model	O
.	O
</s>
<s>
The	O
Plan	B-Operating_System
9	I-Operating_System
operating	B-General_Concept
system	I-General_Concept
pushed	O
this	O
model	O
even	O
further	O
and	O
eliminated	O
the	O
need	O
for	O
additional	O
mechanisms	O
.	O
</s>
<s>
Unix	B-Application
also	O
popularized	O
the	O
hierarchical	B-Application
file	I-Application
system	I-Application
with	O
arbitrarily	O
nested	O
subdirectories	O
,	O
originally	O
introduced	O
by	O
Multics	B-Application
.	O
</s>
<s>
Other	O
common	O
operating	B-General_Concept
systems	I-General_Concept
of	O
the	O
era	O
had	O
ways	O
to	O
divide	O
a	O
storage	O
device	O
into	O
multiple	O
directories	O
or	O
sections	O
,	O
but	O
they	O
had	O
a	O
fixed	O
number	O
of	O
levels	O
,	O
often	O
only	O
one	O
level	O
.	O
</s>
<s>
Several	O
major	O
proprietary	B-Application
operating	B-General_Concept
systems	I-General_Concept
eventually	O
added	O
recursive	O
subdirectory	O
capabilities	O
also	O
patterned	O
after	O
Multics	B-Application
.	O
</s>
<s>
DEC	O
's	O
RSX-11M	B-Application
'	O
s	O
"	O
group	O
,	O
user	O
"	O
hierarchy	O
evolved	O
into	O
OpenVMS	B-Operating_System
directories	O
,	O
CP/M	B-Application
'	O
s	O
volumes	O
evolved	O
into	O
MS-DOS	B-Application
2.0	O
+	O
subdirectories	O
,	O
and	O
HP	O
's	O
MPE	B-Operating_System
group.account	O
hierarchy	O
and	O
IBM	O
's	O
SSP	B-Operating_System
and	O
OS/400	B-Application
library	O
systems	O
were	O
folded	O
into	O
broader	O
POSIX	O
file	B-Application
systems	I-Application
.	O
</s>
<s>
Making	O
the	O
command	O
interpreter	O
an	O
ordinary	O
user-level	B-Operating_System
program	O
,	O
with	O
additional	O
commands	O
provided	O
as	O
separate	O
programs	O
,	O
was	O
another	O
Multics	B-Application
innovation	O
popularized	O
by	O
Unix	B-Application
.	O
</s>
<s>
The	O
Unix	B-Application
shell	I-Application
used	O
the	O
same	O
language	O
for	O
interactive	O
commands	O
as	O
for	O
scripting	O
(	O
shell	B-Language
scripts	I-Language
–	O
there	O
was	O
no	O
separate	O
job	B-Application
control	I-Application
language	I-Application
like	O
IBM	O
's	O
JCL	B-Application
)	O
.	O
</s>
<s>
Since	O
the	O
shell	B-Operating_System
and	O
OS	O
commands	O
were	O
"	O
just	O
another	O
program	O
"	O
,	O
the	O
user	O
could	O
choose	O
(	O
or	O
even	O
write	O
)	O
their	O
own	O
shell	B-Operating_System
.	O
</s>
<s>
New	O
commands	O
could	O
be	O
added	O
without	O
changing	O
the	O
shell	B-Operating_System
itself	O
.	O
</s>
<s>
Unix	B-Application
's	O
innovative	O
command-line	B-Application
syntax	O
for	O
creating	O
modular	B-Architecture
chains	O
of	O
producer-consumer	O
processes	O
(	O
pipelines	B-Operating_System
)	O
made	O
a	O
powerful	O
programming	O
paradigm	O
(	O
coroutines	B-Architecture
)	O
widely	O
available	O
.	O
</s>
<s>
Many	O
later	O
command-line	B-Application
interpreters	O
have	O
been	O
inspired	O
by	O
the	O
Unix	B-Application
shell	I-Application
.	O
</s>
<s>
A	O
fundamental	O
simplifying	O
assumption	O
of	O
Unix	B-Application
was	O
its	O
focus	O
on	O
newline-delimited	O
text	O
for	O
nearly	O
all	O
file	O
formats	O
.	O
</s>
<s>
There	O
were	O
no	O
"	O
binary	O
"	O
editors	O
in	O
the	O
original	O
version	O
of	O
Unix	B-Application
–	O
the	O
entire	O
system	O
was	O
configured	O
using	O
textual	O
shell	B-Operating_System
command	O
scripts	O
.	O
</s>
<s>
The	O
common	O
denominator	O
in	O
the	O
I/O	O
system	O
was	O
the	O
byte	O
–	O
unlike	O
"	B-Application
record-based	I-Application
"	I-Application
file	I-Application
systems	I-Application
.	O
</s>
<s>
The	O
focus	O
on	O
text	O
for	O
representing	O
nearly	O
everything	O
made	O
Unix	B-Operating_System
pipes	I-Operating_System
especially	O
useful	O
and	O
encouraged	O
the	O
development	O
of	O
simple	O
,	O
general	O
tools	O
that	O
could	O
be	O
easily	O
combined	O
to	O
perform	O
more	O
complicated	O
ad	O
hoc	O
tasks	O
.	O
</s>
<s>
The	O
focus	O
on	O
text	O
and	O
bytes	O
made	O
the	O
system	O
far	O
more	O
scalable	O
and	O
portable	B-Architecture
than	O
other	O
systems	O
.	O
</s>
<s>
Over	O
time	O
,	O
text-based	O
applications	O
have	O
also	O
proven	O
popular	O
in	O
application	O
areas	O
,	O
such	O
as	O
printing	O
languages	O
(	O
PostScript	B-Language
,	O
ODF	B-Application
)	O
,	O
and	O
at	O
the	O
application	O
layer	O
of	O
the	O
Internet	B-Protocol
protocols	I-Protocol
,	O
e.g.	O
,	O
FTP	B-Protocol
,	O
SMTP	B-Protocol
,	O
HTTP	B-Protocol
,	O
SOAP	B-Application
,	O
and	O
SIP	B-Application
.	O
</s>
<s>
Unix	B-Application
popularized	O
a	O
syntax	O
for	O
regular	B-Language
expressions	I-Language
that	O
found	O
widespread	O
use	O
.	O
</s>
<s>
The	O
Unix	B-Application
programming	O
interface	O
became	O
the	O
basis	O
for	O
a	O
widely	O
implemented	O
operating	B-General_Concept
system	I-General_Concept
interface	O
standard	O
(	O
POSIX	O
,	O
see	O
above	O
)	O
.	O
</s>
<s>
The	O
C	B-Language
programming	I-Language
language	I-Language
soon	O
spread	O
beyond	O
Unix	B-Application
,	O
and	O
is	O
now	O
ubiquitous	O
in	O
systems	O
and	O
applications	O
programming	O
.	O
</s>
<s>
Early	O
Unix	B-Application
developers	O
were	O
important	O
in	O
bringing	O
the	O
concepts	O
of	O
modularity	B-Architecture
and	O
reusability	B-Application
into	O
software	B-General_Concept
engineering	I-General_Concept
practice	O
,	O
spawning	O
a	O
"	O
software	B-Application
tools	I-Application
"	O
movement	O
.	O
</s>
<s>
Over	O
time	O
,	O
the	O
leading	O
developers	O
of	O
Unix	B-Application
(	O
and	O
programs	O
that	O
ran	O
on	O
it	O
)	O
established	O
a	O
set	O
of	O
cultural	O
norms	O
for	O
developing	O
software	O
,	O
norms	O
which	O
became	O
as	O
important	O
and	O
influential	O
as	O
the	O
technology	O
of	O
Unix	B-Application
itself	O
;	O
this	O
has	O
been	O
termed	O
the	B-Operating_System
Unix	I-Operating_System
philosophy	I-Operating_System
.	O
</s>
<s>
The	O
TCP/IP	B-Protocol
networking	I-Protocol
protocols	I-Protocol
were	O
quickly	O
implemented	O
on	O
the	O
Unix	B-Application
versions	O
widely	O
used	O
on	O
relatively	O
inexpensive	O
computers	O
,	O
which	O
contributed	O
to	O
the	O
Internet	O
explosion	O
of	O
worldwide	O
real-time	O
connectivity	O
,	O
and	O
which	O
formed	O
the	O
basis	O
for	O
implementations	O
on	O
many	O
other	O
platforms	O
.	O
</s>
<s>
The	O
Unix	B-Application
policy	O
of	O
extensive	O
on-line	O
documentation	O
and	O
(	O
for	O
many	O
years	O
)	O
ready	O
access	O
to	O
all	O
system	O
source	O
code	O
raised	O
programmer	O
expectations	O
,	O
and	O
contributed	O
to	O
the	O
launch	O
of	O
the	O
free	B-Application
software	I-Application
movement	O
in	O
1983	O
.	O
</s>
<s>
In	O
1983	O
,	O
Richard	O
Stallman	O
announced	O
the	O
GNU	B-Operating_System
(	O
short	O
for	O
"	O
GNU	B-Operating_System
's	I-Operating_System
Not	I-Operating_System
Unix	I-Operating_System
"	O
)	O
project	O
,	O
an	O
ambitious	O
effort	O
to	O
create	O
a	O
free	B-Application
software	I-Application
Unix-like	B-Operating_System
system	I-Operating_System
—	O
"	O
free	B-Application
"	O
in	O
the	O
sense	O
that	O
everyone	O
who	O
received	O
a	O
copy	O
would	O
be	O
free	B-Application
to	O
use	O
,	O
study	O
,	O
modify	O
,	O
and	O
redistribute	O
it	O
.	O
</s>
<s>
The	O
GNU	B-Operating_System
project	O
's	O
own	O
kernel	B-Operating_System
development	O
project	O
,	O
GNU	B-Application
Hurd	I-Application
,	O
had	O
not	O
yet	O
produced	O
a	O
working	O
kernel	B-Operating_System
,	O
but	O
in	O
1991	O
Linus	O
Torvalds	O
released	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
as	O
free	B-Application
software	I-Application
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
In	O
addition	O
to	O
their	O
use	O
in	O
the	B-Operating_System
GNU	I-Operating_System
operating	I-Operating_System
system	I-Operating_System
,	O
many	O
GNU	B-Operating_System
packages	O
–	O
such	O
as	O
the	O
GNU	B-Application
Compiler	I-Application
Collection	I-Application
(	O
and	O
the	O
rest	O
of	O
the	O
GNU	B-Application
toolchain	I-Application
)	O
,	O
the	O
GNU	B-Language
C	I-Language
library	I-Language
and	O
the	O
GNU	B-Application
Core	I-Application
Utilities	I-Application
–	O
have	O
gone	O
on	O
to	O
play	O
central	O
roles	O
in	O
other	O
free	B-Application
Unix	B-Operating_System
systems	I-Operating_System
as	O
well	O
.	O
</s>
<s>
Linux	B-Application
distributions	I-Application
,	O
consisting	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
and	O
large	O
collections	O
of	O
compatible	O
software	O
have	O
become	O
popular	O
both	O
with	O
individual	O
users	O
and	O
in	O
business	O
.	O
</s>
<s>
Popular	O
distributions	O
include	O
Red	O
Hat	O
Enterprise	O
Linux	B-Operating_System
,	O
Fedora	O
,	O
SUSE	O
Linux	B-Operating_System
Enterprise	O
,	O
openSUSE	B-Operating_System
,	O
Debian	O
,	O
Ubuntu	B-Operating_System
,	O
Linux	B-Application
Mint	I-Application
,	O
Mandriva	O
Linux	B-Operating_System
,	O
Slackware	B-Application
Linux	I-Application
,	O
Arch	O
Linux	B-Operating_System
and	O
Gentoo	B-Application
.	O
</s>
<s>
A	O
free	B-Application
derivative	O
of	O
BSD	B-Operating_System
Unix	I-Operating_System
,	O
386BSD	B-Operating_System
,	O
was	O
released	O
in	O
1992	O
and	O
led	O
to	O
the	O
NetBSD	B-Device
and	O
FreeBSD	B-Operating_System
projects	I-Operating_System
.	O
</s>
<s>
With	O
the	O
1994	O
settlement	O
of	O
a	O
lawsuit	O
brought	O
against	O
the	O
University	O
of	O
California	O
and	O
Berkeley	O
Software	O
Design	O
Inc	O
.	O
(	O
USL	B-Operating_System
v	I-Operating_System
.	I-Operating_System
BSDi	I-Operating_System
)	O
by	O
Unix	B-Application
System	I-Application
Laboratories	O
,	O
it	O
was	O
clarified	O
that	O
Berkeley	O
had	O
the	O
right	O
to	O
distribute	O
BSD	B-Operating_System
Unix	I-Operating_System
for	O
free	B-Application
if	O
it	O
so	O
desired	O
.	O
</s>
<s>
Since	O
then	O
,	O
BSD	B-Operating_System
Unix	I-Operating_System
has	O
been	O
developed	O
in	O
several	O
different	O
product	O
branches	O
,	O
including	O
OpenBSD	B-Operating_System
and	O
DragonFly	B-Application
BSD	I-Application
.	O
</s>
<s>
Linux	B-Operating_System
and	O
BSD	B-Operating_System
are	O
increasingly	O
filling	O
the	O
market	O
needs	O
traditionally	O
served	O
by	O
proprietary	B-Application
Unix	B-Application
operating	I-Application
systems	I-Application
,	O
as	O
well	O
as	O
expanding	O
into	O
new	O
markets	O
such	O
as	O
the	O
consumer	O
desktop	O
and	O
mobile	B-Application
and	I-Application
embedded	I-Application
devices	I-Application
.	O
</s>
<s>
Because	O
of	O
the	O
modular	B-Architecture
design	O
of	O
the	O
Unix	B-Application
model	O
,	O
sharing	O
components	O
is	O
relatively	O
common	O
;	O
consequently	O
,	O
most	O
or	O
all	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
systems	I-Operating_System
include	O
at	O
least	O
some	O
BSD	B-Operating_System
code	O
,	O
and	O
some	O
systems	O
also	O
include	O
GNU	B-Operating_System
utilities	O
in	O
their	O
distributions	O
.	O
</s>
<s>
In	O
a	O
1999	O
interview	O
,	O
Dennis	O
Ritchie	O
voiced	O
his	O
opinion	O
that	O
Linux	B-Operating_System
and	O
BSD	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
are	O
a	O
continuation	O
of	O
the	O
basis	O
of	O
the	O
Unix	B-Application
design	O
,	O
and	O
are	O
derivatives	O
of	O
Unix	B-Application
:	O
</s>
<s>
In	O
the	O
same	O
interview	O
,	O
he	O
states	O
that	O
he	O
views	O
both	O
Unix	B-Application
and	O
Linux	B-Operating_System
as	O
"	O
the	O
continuation	O
of	O
ideas	O
that	O
were	O
started	O
by	O
Ken	O
and	O
me	O
and	O
many	O
others	O
,	O
many	O
years	O
ago	O
"	O
.	O
</s>
<s>
OpenSolaris	B-Operating_System
was	O
the	O
free	B-Application
software	I-Application
counterpart	O
to	O
Solaris	B-Application
developed	O
by	O
Sun	O
Microsystems	O
,	O
which	O
included	O
a	O
CDDL-licensed	O
kernel	B-Operating_System
and	O
a	O
primarily	O
GNU	B-Operating_System
userland	O
.	O
</s>
<s>
However	O
,	O
Oracle	B-Application
discontinued	O
the	O
project	O
upon	O
their	O
acquisition	O
of	O
Sun	O
,	O
which	O
prompted	O
a	O
group	O
of	O
former	O
Sun	O
employees	O
and	O
members	O
of	O
the	O
OpenSolaris	B-Operating_System
community	O
to	O
fork	O
OpenSolaris	B-Operating_System
into	O
the	O
illumos	B-Application
kernel	B-Operating_System
.	O
</s>
<s>
As	O
of	O
2014	O
,	O
illumos	B-Application
remains	O
the	O
only	O
active	O
open-source	B-Application
System	B-Operating_System
V	I-Operating_System
derivative	O
.	O
</s>
<s>
In	O
May	O
1975	O
,	O
RFC	O
681	O
described	O
the	O
development	O
of	O
Network	O
Unix	B-Application
by	O
the	O
Center	O
for	O
Advanced	O
Computation	O
at	O
the	O
University	O
of	O
Illinois	O
Urbana-Champaign	O
.	O
</s>
<s>
The	O
Unix	B-Application
system	I-Application
was	O
said	O
to	O
"	O
present	O
several	O
interesting	O
capabilities	O
as	O
an	O
ARPANET	O
mini-host	O
"	O
.	O
</s>
<s>
At	O
the	O
time	O
,	O
Unix	B-Application
required	O
a	O
license	O
from	O
Bell	O
Telephone	O
Laboratories	O
that	O
cost	O
US$	O
20,000	O
for	O
non-university	O
institutions	O
,	O
while	O
universities	O
could	O
obtain	O
a	O
license	O
for	O
a	O
nominal	O
fee	O
of	O
$150	O
.	O
</s>
<s>
The	O
RFC	O
specifically	O
mentions	O
that	O
Unix	B-Application
"	O
offers	O
powerful	O
local	O
processing	O
facilities	O
in	O
terms	O
of	O
user	O
programs	O
,	O
several	O
compilers	B-Language
,	O
an	O
editor	B-Application
based	O
on	O
QED	B-Application
,	O
a	O
versatile	O
document	O
preparation	O
system	O
,	O
and	O
an	O
efficient	O
file	B-Application
system	I-Application
featuring	O
sophisticated	O
access	O
control	O
,	O
mountable	B-Application
and	O
de-mountable	O
volumes	O
,	O
and	O
a	O
unified	O
treatment	O
of	O
peripherals	O
as	O
special	O
files.	O
"	O
</s>
<s>
The	O
latter	O
permitted	O
the	O
Network	B-Protocol
Control	I-Protocol
Program	I-Protocol
(	O
NCP	O
)	O
to	O
be	O
integrated	O
within	O
the	O
Unix	B-Application
file	I-Application
system	I-Application
,	O
treating	O
network	B-Architecture
connections	I-Architecture
as	O
special	B-Application
files	I-Application
that	O
could	O
be	O
accessed	O
through	O
standard	O
Unix	B-Application
I/O	B-Operating_System
calls	I-Operating_System
,	O
which	O
included	O
the	O
added	O
benefit	O
of	O
closing	O
all	O
connections	O
on	O
program	O
exit	O
,	O
should	O
the	O
user	O
neglect	O
to	O
do	O
so	O
.	O
</s>
<s>
In	O
order	O
"	O
to	O
minimize	O
the	O
amount	O
of	O
code	O
added	O
to	O
the	O
basic	O
Unix	B-Application
kernel	B-Operating_System
"	O
,	O
much	O
of	O
the	O
NCP	O
code	O
ran	O
in	O
a	O
swappable	B-Architecture
user	O
process	O
,	O
running	O
only	O
when	O
needed	O
.	O
</s>
<s>
In	O
October	O
1993	O
,	O
Novell	O
,	O
the	O
company	O
that	O
owned	O
the	O
rights	O
to	O
the	O
Unix	B-Operating_System
System	I-Operating_System
V	I-Operating_System
source	O
at	O
the	O
time	O
,	O
transferred	O
the	O
trademarks	O
of	O
Unix	B-Application
to	O
the	O
X/Open	O
Company	O
(	O
now	O
The	B-Application
Open	I-Application
Group	I-Application
)	O
,	O
and	O
in	O
1995	O
sold	O
the	O
related	O
business	O
operations	O
to	O
Santa	O
Cruz	O
Operation	O
(	O
SCO	O
)	O
.	O
</s>
<s>
Unix	B-Application
vendor	O
SCO	O
Group	O
Inc	O
.	O
accused	O
Novell	O
of	O
slander	O
of	O
title	O
.	O
</s>
<s>
The	O
present	O
owner	O
of	O
the	O
trademark	O
UNIX	B-Application
is	O
The	B-Application
Open	I-Application
Group	I-Application
,	O
an	O
industry	O
standards	O
consortium	O
.	O
</s>
<s>
Only	O
systems	O
fully	O
compliant	O
with	O
and	O
certified	O
to	O
the	O
Single	O
UNIX	B-Application
Specification	O
qualify	O
as	O
"	O
UNIX	B-Application
"	O
(	O
others	O
are	O
called	O
"	O
Unix-like	B-Operating_System
"	O
)	O
.	O
</s>
<s>
By	O
decree	O
of	O
The	B-Application
Open	I-Application
Group	I-Application
,	O
the	O
term	O
"	O
UNIX	B-Application
"	O
refers	O
more	O
to	O
a	O
class	O
of	O
operating	B-General_Concept
systems	I-General_Concept
than	O
to	O
a	O
specific	O
implementation	O
of	O
an	O
operating	B-General_Concept
system	I-General_Concept
;	O
those	O
operating	B-General_Concept
systems	I-General_Concept
which	O
meet	O
The	B-Application
Open	I-Application
Group	I-Application
's	O
Single	O
UNIX	B-Application
Specification	O
should	O
be	O
able	O
to	O
bear	O
the	O
UNIX	B-Application
98	O
or	O
UNIX	B-Application
03	O
trademarks	O
today	O
,	O
after	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
vendor	O
pays	O
a	O
substantial	O
certification	O
fee	O
and	O
annual	O
trademark	O
royalties	O
to	O
The	B-Application
Open	I-Application
Group	I-Application
.	O
</s>
<s>
Systems	O
that	O
have	O
been	O
licensed	O
to	O
use	O
the	O
UNIX	B-Application
trademark	O
include	O
AIX	B-Application
,	O
EulerOS	O
,	O
HP-UX	B-Application
,	O
Inspur	O
K-UX	O
,	O
IRIX	B-Operating_System
,	O
macOS	B-Application
,	O
Solaris	B-Application
,	O
Tru64	B-Operating_System
UNIX	I-Operating_System
(	O
formerly	O
"	O
Digital	B-Operating_System
UNIX	I-Operating_System
"	O
,	O
or	O
OSF/1	B-Operating_System
)	O
,	O
and	O
z/OS	B-Application
.	O
</s>
<s>
Notably	O
,	O
EulerOS	O
and	O
Inspur	O
K-UX	O
are	O
Linux	B-Application
distributions	I-Application
certified	O
as	O
UNIX03	O
compliant	O
.	O
</s>
<s>
Sometimes	O
a	O
representation	O
like	O
Un*x	B-Operating_System
,	O
*	B-Operating_System
NIX	I-Operating_System
,	O
or	O
*	O
N	O
?	O
X	B-Operating_System
is	O
used	O
to	O
indicate	O
all	O
operating	B-General_Concept
systems	I-General_Concept
similar	O
to	O
Unix	B-Application
.	O
</s>
<s>
This	O
notation	O
is	O
also	O
used	O
to	O
describe	O
other	O
Unix-like	B-Operating_System
systems	I-Operating_System
that	O
have	O
not	O
met	O
the	O
requirements	O
for	O
UNIX	B-Application
branding	O
from	O
the	B-Application
Open	I-Application
Group	I-Application
.	O
</s>
<s>
The	B-Application
Open	I-Application
Group	I-Application
requests	O
that	O
UNIX	B-Application
always	O
be	O
used	O
as	O
an	O
adjective	O
followed	O
by	O
a	O
generic	O
term	O
such	O
as	O
system	O
to	O
help	O
avoid	O
the	O
creation	O
of	O
a	O
genericized	O
trademark	O
.	O
</s>
<s>
Unix	B-Application
was	O
the	O
original	O
formatting	O
,	O
but	O
the	O
usage	O
of	O
UNIX	B-Application
remains	O
widespread	O
because	O
it	O
was	O
once	O
typeset	O
in	O
small	O
caps	O
(	O
Unix	B-Application
)	O
.	O
</s>
<s>
According	O
to	O
Dennis	O
Ritchie	O
,	O
when	O
presenting	O
the	O
original	O
Unix	B-Application
paper	O
to	O
the	O
third	O
Operating	B-General_Concept
Systems	I-General_Concept
Symposium	O
of	O
the	O
American	O
Association	O
for	O
Computing	O
Machinery	O
(	O
ACM	O
)	O
,	O
"	O
we	O
had	O
a	O
new	O
typesetter	O
and	O
troff	B-Language
had	O
just	O
been	O
invented	O
and	O
we	O
were	O
intoxicated	O
by	O
being	O
able	O
to	O
produce	O
small	O
caps	O
"	O
.	O
</s>
<s>
Many	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
predecessors	O
and	O
contemporaries	O
used	O
all-uppercase	O
lettering	O
,	O
so	O
many	O
people	O
wrote	O
the	O
name	O
in	O
upper	O
case	O
due	O
to	O
force	O
of	O
habit	O
.	O
</s>
<s>
The	O
result	O
is	O
that	O
Unix	B-Application
has	O
been	O
used	O
as	O
a	O
brand	O
name	O
for	O
various	O
products	O
including	O
bookshelves	O
,	O
ink	O
pens	O
,	O
bottled	O
glue	O
,	O
diapers	O
,	O
hair	O
driers	O
and	O
food	O
containers	O
.	O
</s>
<s>
Several	O
plural	O
forms	O
of	O
Unix	B-Application
are	O
used	O
casually	O
to	O
refer	B-Application
to	O
multiple	O
brands	O
of	O
Unix	B-Application
and	O
Unix-like	B-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
Most	O
common	O
is	O
the	O
conventional	O
Unixes	B-Application
,	O
but	O
Unices	B-Operating_System
,	O
treating	O
Unix	B-Application
as	O
a	O
Latin	O
noun	O
of	O
the	O
third	O
declension	O
,	O
is	O
also	O
popular	O
.	O
</s>
<s>
The	O
pseudo-Anglo-Saxon	O
plural	O
form	O
Unixen	B-Operating_System
is	O
not	O
common	O
,	O
although	O
occasionally	O
seen	O
.	O
</s>
<s>
Sun	O
Microsystems	O
,	O
developer	O
of	O
the	O
Solaris	B-Application
variant	O
,	O
has	O
asserted	O
that	O
the	O
term	O
Unix	B-Application
is	O
itself	O
plural	O
,	O
referencing	O
its	O
many	O
implementations	O
.	O
</s>
