<s>
RISC/os	B-Operating_System
is	O
a	O
discontinued	O
UNIX	B-Application
operating	I-Application
system	I-Application
developed	O
by	O
MIPS	O
Computer	O
Systems	O
,	O
Inc	O
.	O
from	O
1985	O
to	O
1992	O
,	O
for	O
their	O
computer	B-Device
workstations	I-Device
and	O
servers	O
,	O
including	O
such	O
models	O
as	O
the	O
MIPS	O
M/120	O
server	B-Application
and	O
MIPS	B-Device
Magnum	I-Device
workstation	B-Device
.	O
</s>
<s>
It	O
was	O
also	O
known	O
as	O
UMIPS	B-Operating_System
or	O
MIPS	B-Operating_System
OS	I-Operating_System
.	O
</s>
<s>
RISC/os	B-Operating_System
was	O
based	O
largely	O
on	O
UNIX	B-Operating_System
System	I-Operating_System
V	I-Operating_System
with	O
additions	O
from	O
4.3BSD	B-Operating_System
UNIX	B-Application
,	O
ported	O
to	O
the	O
MIPS	B-Device
architecture	I-Device
.	O
</s>
<s>
It	O
was	O
a	O
"	O
dual-universe	B-Operating_System
"	O
operating	B-General_Concept
system	I-General_Concept
,	O
meaning	O
that	O
it	O
had	O
separate	O
,	O
switchable	O
runtime	O
environments	O
providing	O
compatibility	O
with	O
either	O
System	B-Operating_System
V	I-Operating_System
Release	I-Operating_System
3	I-Operating_System
or	O
4.3BSD	B-Operating_System
.	O
</s>
<s>
MIPS	B-Operating_System
OS	I-Operating_System
was	O
one	O
of	O
the	O
first	O
32-bit	O
operating	B-General_Concept
systems	I-General_Concept
for	O
RISC-based	B-Architecture
workstation-class	O
computers	O
.	O
</s>
<s>
It	O
was	O
also	O
one	O
of	O
the	O
first	O
64-bit	B-Device
Unix	B-Application
releases	O
for	O
RISC	B-Architecture
based	O
microprocessors	O
,	O
with	O
the	O
first	O
64-bit	B-Device
versions	O
appearing	O
in	O
1990	O
.	O
</s>
<s>
MIPS	B-Operating_System
OS	I-Operating_System
supported	O
full	O
32-bit	O
and	O
64-bit	B-Device
applications	O
simultaneously	O
using	O
the	O
underlying	O
hardware	O
architecture	O
supporting	O
the	O
MIPS-IV	O
instruction	O
set	O
.	O
</s>
<s>
Later	O
releases	O
added	O
support	O
for	O
System	B-Operating_System
V	I-Operating_System
Release	O
4	O
compatibility	O
,	O
R6000	B-Device
processor	O
support	O
and	O
later	O
symmetric	B-Operating_System
multiprocessing	I-Operating_System
support	O
on	O
the	O
R4400	O
and	O
R6000	B-Device
processors	O
.	O
</s>
<s>
During	O
the	O
early	O
1990s	O
,	O
several	O
vendors	O
including	O
DEC	O
,	O
Silicon	O
Graphics	O
,	O
and	O
Ardent	O
licensed	O
portions	O
of	O
the	O
software	O
MIPS	O
had	O
written	O
for	O
the	O
RISC/os	B-Operating_System
for	O
their	O
own	O
Unix	B-Application
variants	O
.	O
</s>
<s>
Evans	O
&	O
Sutherland	O
licensed	O
RISC/os	B-Operating_System
directly	O
for	O
its	O
ESV	O
series	O
workstations	B-Device
.	O
</s>
<s>
MIPS	O
 '	O
influence	O
was	O
most	O
visible	O
as	O
the	O
C	O
compiler	O
and	O
development	O
tools	O
shared	O
by	O
virtually	O
all	O
commercial	O
Unixes	B-Application
for	O
the	O
MIPS	O
processor	O
,	O
the	O
low	O
memory	O
operating	B-General_Concept
system	I-General_Concept
code	O
,	O
and	O
the	O
ROM	O
code	O
for	O
MIPS	O
processors	O
.	O
</s>
<s>
Because	O
of	O
its	O
early	O
UNIX	B-Application
heritage	O
,	O
RISC/os	B-Operating_System
was	O
limited	O
in	O
comparison	O
to	O
modern	O
UNIX	B-Application
variants	O
for	O
example	O
,	O
even	O
the	O
last	O
releases	O
of	O
RISC/os	B-Operating_System
did	O
not	O
support	O
shared	B-Library
libraries	I-Library
.	O
</s>
<s>
Support	O
for	O
RISC/os	B-Operating_System
was	O
subsequently	O
phased	O
out	O
.	O
</s>
