<s>
The	O
Newcastle	B-Protocol
Connection	I-Protocol
(	O
or	O
UNIX	O
United	O
)	O
was	O
a	O
software	O
subsystem	O
from	O
the	O
early	O
1980s	O
that	O
could	O
be	O
added	O
to	O
each	O
of	O
a	O
set	O
of	O
interconnected	O
UNIX-like	O
systems	O
to	O
build	O
a	O
distributed	O
system	O
.	O
</s>
<s>
It	O
became	O
a	O
forerunner	O
of	O
Sun	O
Microsystems	O
 '	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
(	O
NFS	O
)	O
.	O
</s>
<s>
The	O
term	O
"	O
UNIX	O
United	O
"	O
describes	O
the	O
scheme	O
of	O
combining	O
the	O
overall	O
filesystems	O
of	O
the	O
participating	O
UNIX	O
machines	O
;	O
"	O
Newcastle	B-Protocol
Connection	I-Protocol
"	O
describes	O
the	O
underlying	O
communication	O
layer	O
which	O
enables	O
this	O
.	O
</s>
<s>
A	O
UNIX	O
United	O
system	O
constructed	O
with	O
the	O
Newcastle	B-Protocol
Connection	I-Protocol
is	O
functionally	O
indistinguishable	O
from	O
a	O
centralised	O
UNIX	O
system	O
at	O
the	O
system-call	O
level	O
.	O
</s>
<s>
Rather	O
,	O
it	O
ran	O
in	O
user-space	O
,	O
using	O
a	O
modified	O
version	O
of	O
the	B-Language
C	I-Language
standard	I-Language
library	I-Language
of	O
its	O
day	O
which	O
was	O
capable	O
of	O
recognising	O
these	O
new	O
semantics	O
.	O
</s>
<s>
A	O
match	O
would	O
divert	O
such	O
a	O
reference	O
through	O
to	O
the	O
new	O
software	O
,	O
which	O
then	O
used	O
remote	B-Operating_System
procedure	I-Operating_System
calls	I-Operating_System
to	O
the	O
remote	O
machine	O
.	O
</s>
<s>
The	O
second	O
,	O
however	O
,	O
is	O
diverted	O
into	O
the	O
"	O
Newcastle	B-Protocol
Connection	I-Protocol
"	O
software	O
because	O
of	O
the	O
filename	O
's	O
leading	O
"	O
/..	O
"	O
.	O
</s>
<s>
The	O
original	O
implementation	O
at	O
Newcastle	O
was	O
for	O
UNIX	O
V7	O
on	O
a	O
set	O
of	O
PDP-11	B-Device
computers	O
connected	O
by	O
a	O
Cambridge	B-General_Concept
Ring	I-General_Concept
network	O
.	O
</s>
<s>
Subsequent	O
implementations	O
added	O
support	O
for	O
other	O
versions	O
of	O
UNIX	O
(	O
including	O
BSD	B-Operating_System
4.2	I-Operating_System
and	O
System	B-Operating_System
V	I-Operating_System
)	O
,	O
network	O
technologies	O
,	O
protocols	O
and	O
hardware	O
architecture	O
(	O
VAX	B-Device
,	O
Motorola	B-Device
68000	I-Device
)	O
.	O
</s>
