<s>
UNICOS	B-Operating_System
is	O
a	O
range	O
of	O
Unix	B-Application
and	O
after	O
it	O
Linux	B-Application
operating	I-Application
system	I-Application
(	O
OS	O
)	O
variants	O
developed	O
by	O
Cray	O
for	O
its	O
supercomputers	B-Architecture
.	O
</s>
<s>
UNICOS	B-Operating_System
is	O
the	O
successor	O
of	O
the	O
Cray	B-Operating_System
Operating	I-Operating_System
System	I-Operating_System
(	O
COS	O
)	O
.	O
</s>
<s>
It	O
provides	O
network	O
clustering	B-Architecture
and	O
source	O
code	O
compatibility	B-General_Concept
layers	I-General_Concept
for	O
some	O
other	O
Unixes	B-Application
.	O
</s>
<s>
UNICOS	B-Operating_System
was	O
originally	O
introduced	O
in	O
1985	O
with	O
the	O
Cray-2	B-Device
system	O
and	O
later	O
ported	O
to	O
other	O
Cray	O
models	O
.	O
</s>
<s>
The	O
original	O
UNICOS	B-Operating_System
was	O
based	O
on	O
UNIX	B-Operating_System
System	I-Operating_System
V	I-Operating_System
Release	O
2	B-Device
,	O
and	O
had	O
many	O
Berkeley	B-Operating_System
Software	I-Operating_System
Distribution	I-Operating_System
(	O
BSD	B-Operating_System
)	O
features	O
(	O
e.g.	O
,	O
computer	B-Architecture
networking	I-Architecture
and	O
file	B-Application
system	I-Application
enhancements	O
)	O
added	O
to	O
it	O
.	O
</s>
<s>
CX-OS	O
was	O
the	O
original	O
name	O
given	O
to	O
what	O
is	O
now	O
UNICOS	B-Operating_System
.	O
</s>
<s>
This	O
was	O
a	O
prototype	O
system	O
which	O
ran	O
on	O
a	O
Cray	B-Device
X-MP	I-Device
in	O
1984	O
before	O
the	O
Cray-2	B-Device
port	O
.	O
</s>
<s>
It	O
was	O
used	O
to	O
demonstrate	O
the	O
feasibility	O
of	O
using	O
Unix	B-Application
on	O
a	O
supercomputer	B-Architecture
system	O
,	O
before	O
Cray-2	B-Device
hardware	O
was	O
available	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
revamp	O
was	O
part	O
of	O
a	O
larger	O
movement	O
inside	O
Cray	O
Research	O
to	O
modernize	O
their	O
corporate	O
software	O
:	O
including	O
rewriting	O
their	O
most	O
important	O
Fortran	B-Application
compiler	O
(	O
cft	O
to	O
cft77	O
)	O
in	O
a	O
higher-level	O
language	O
(	O
Pascal	B-Application
)	O
with	O
more	O
modern	O
optimizations	O
and	O
vectorizations	O
.	O
</s>
<s>
As	O
a	O
migration	O
path	O
for	O
existing	O
COS	O
customers	O
wishing	O
to	O
transition	O
to	O
UNICOS	B-Operating_System
,	O
a	O
Guest	O
Operating	B-General_Concept
System	I-General_Concept
(	O
GOS	O
)	O
capability	O
was	O
introduced	O
into	O
COS	O
.	O
</s>
<s>
The	O
only	O
guest	O
OS	O
that	O
was	O
ever	O
supported	O
was	O
UNICOS	B-Operating_System
.	O
</s>
<s>
A	O
COS	O
batch	O
job	O
would	O
be	O
submitted	O
to	O
start	O
up	O
UNICOS	B-Operating_System
,	O
which	O
would	O
then	O
run	O
as	O
a	O
subsystem	O
under	O
COS	O
,	O
using	O
a	O
subset	O
of	O
the	O
systems	O
CPUs	O
,	O
memory	O
,	O
and	O
peripheral	O
devices	O
.	O
</s>
<s>
The	O
UNICOS	B-Operating_System
that	O
ran	O
under	O
GOS	O
was	O
exactly	O
the	O
same	O
as	O
when	O
it	O
ran	O
stand-alone	O
:	O
the	O
difference	O
was	O
that	O
the	O
kernel	B-Operating_System
would	O
make	O
certain	O
low-level	O
hardware	O
requests	O
through	O
the	O
COS	O
GOS	O
hook	O
,	O
rather	O
than	O
directly	O
to	O
the	O
hardware	O
.	O
</s>
<s>
One	O
of	O
the	O
sites	O
that	O
ran	O
very	O
early	O
versions	O
of	O
UNICOS	B-Operating_System
was	O
Bell	O
Labs	O
,	O
where	O
Unix	B-Application
pioneers	O
including	O
Dennis	O
Ritchie	O
ported	O
parts	O
of	O
their	O
Eighth	B-Operating_System
Edition	I-Operating_System
Unix	I-Operating_System
(	O
including	O
STREAMS	B-Operating_System
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
)	O
to	O
UNICOS	B-Operating_System
.	O
</s>
<s>
They	O
also	O
experimented	O
with	O
a	O
guest	O
facility	O
within	O
UNICOS	B-Operating_System
,	O
allowing	O
the	O
stand-alone	O
version	O
of	O
the	O
OS	O
to	O
host	O
itself	O
.	O
</s>
<s>
Cray	O
released	O
several	O
different	O
OSs	O
under	O
the	O
name	O
UNICOS	B-Operating_System
,	O
including	O
:	O
</s>
<s>
UNICOS	B-Operating_System
:	O
the	O
original	O
Cray	O
Unix	B-Application
,	O
based	O
on	O
System	B-Operating_System
V	I-Operating_System
.	O
Used	O
on	O
the	O
Cray-1	B-Device
,	O
Cray-2	B-Device
,	O
X-MP	B-Device
,	O
Y-MP	B-Device
,	O
C90	B-Device
,	O
etc	O
.	O
</s>
<s>
UNICOS	B-Operating_System
MAX	O
:	O
a	O
Mach-based	O
microkernel	B-Operating_System
used	O
on	O
the	O
T3D	B-Device
's	O
processing	O
elements	O
,	O
together	O
with	O
UNICOS	B-Operating_System
on	O
the	O
host	O
Y-MP	B-Device
or	O
C90	B-Device
system	O
.	O
</s>
<s>
UNICOS/mk	O
:	O
a	O
serverized	O
version	O
of	O
UNICOS	B-Operating_System
using	O
the	O
Chorus	B-Operating_System
microkernel	B-Operating_System
to	O
make	O
a	O
distributed	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
.	O
</s>
<s>
Used	O
on	O
the	O
T3E	B-Device
.	O
</s>
<s>
This	O
was	O
the	O
last	O
Cray	O
OS	O
really	O
based	O
on	O
UNICOS	B-Operating_System
sources	O
,	O
as	O
the	O
following	O
products	O
were	O
based	O
on	O
different	O
sources	O
and	O
simply	O
used	O
the	O
"	O
UNICOS	B-Operating_System
"	O
name	O
.	O
</s>
<s>
UNICOS/mp	O
:	O
not	O
derived	O
from	O
UNICOS	B-Operating_System
,	O
but	O
based	O
on	O
IRIX	B-Operating_System
6.5	O
.	O
</s>
<s>
Used	O
on	O
the	O
X1	B-Device
.	O
</s>
<s>
UNICOS/lc	O
:	O
not	O
derived	O
from	O
UNICOS	B-Operating_System
,	O
but	O
based	O
on	O
SUSE	O
Linux	B-Operating_System
.	O
</s>
<s>
Used	O
on	O
the	O
XT3	B-Device
,	O
XT4	B-Device
and	O
XT5	B-Device
.	O
</s>
