<s>
Sixth	B-Operating_System
Edition	I-Operating_System
Unix	I-Operating_System
,	O
also	O
called	O
Version	B-Operating_System
6	I-Operating_System
Unix	I-Operating_System
or	O
just	O
V6	O
,	O
was	O
the	O
first	O
version	O
of	O
the	O
Unix	B-Application
operating	I-Application
system	I-Application
to	O
see	O
wide	O
release	O
outside	O
Bell	O
Labs	O
.	O
</s>
<s>
It	O
was	O
released	O
in	O
May	O
1975	O
and	O
,	O
like	O
its	O
direct	O
predecessor	O
,	O
targeted	O
the	O
DEC	B-Device
PDP-11	I-Device
family	O
of	O
minicomputers	B-Architecture
.	O
</s>
<s>
It	O
was	O
superseded	O
by	O
Version	B-Operating_System
7	I-Operating_System
Unix	I-Operating_System
in	O
1978/1979	O
,	O
although	O
V6	O
systems	O
remained	O
in	O
regular	O
operation	O
until	O
at	O
least	O
1985	O
.	O
</s>
<s>
AT&T	O
Corporation	O
licensed	O
Version	B-Operating_System
5	I-Operating_System
Unix	I-Operating_System
to	O
educational	O
institutions	O
only	O
,	O
but	O
licensed	O
Version	O
6	O
also	O
to	O
commercial	O
users	O
for	O
$20	O
,	O
000	O
,	O
and	O
it	O
remained	O
the	O
most	O
widely	O
used	O
version	O
into	O
the	O
1980s	O
.	O
</s>
<s>
An	O
enhanced	O
V6	O
was	O
the	O
basis	O
of	O
the	O
first	O
ever	O
commercially	O
sold	O
Unix	B-Application
version	O
,	O
INTERACTIVE	B-Operating_System
's	O
IS/1	O
.	O
</s>
<s>
Bell	O
's	O
own	O
PWB/UNIX	B-Operating_System
1.0	O
was	O
also	O
based	O
on	O
V6	O
,	O
where	O
earlier	O
(	O
unreleased	O
)	O
versions	O
were	O
based	O
on	O
V4	O
and	O
V5	O
.	O
</s>
<s>
Whitesmiths	O
produced	O
and	O
marketed	O
a	O
(	O
binary-compatible	O
)	O
V6	O
clone	O
under	O
the	O
name	O
Idris	B-Operating_System
.	O
</s>
<s>
V6	B-Operating_System
Unix	I-Operating_System
was	O
released	O
as	O
a	O
distribution	O
including	O
the	O
full	O
source	O
code	O
.	O
</s>
<s>
UC	O
Berkeley	O
distributed	O
a	O
set	O
of	O
add-on	O
programs	O
called	O
the	O
First	B-Operating_System
Berkeley	I-Operating_System
Software	I-Operating_System
Distribution	I-Operating_System
or	O
1BSD	O
,	O
which	O
later	O
became	O
a	O
complete	O
operating	B-General_Concept
system	I-General_Concept
distribution	O
.	O
</s>
<s>
UNSW	O
professor	O
John	O
Lions	O
 '	O
famous	O
Commentary	O
on	O
UNIX	B-Application
6th	O
Edition	O
was	O
an	O
edited	O
selection	O
of	O
the	O
main	O
parts	O
of	O
the	O
kernel	O
as	O
implemented	O
for	O
a	O
Digital	O
PDP-11/40	B-Device
,	O
and	O
was	O
the	O
main	O
source	O
of	O
kernel	O
documentation	O
for	O
many	O
early	O
Unix	B-Application
developers	O
.	O
</s>
<s>
Due	O
to	O
license	O
restrictions	O
on	O
later	O
Unix	B-Application
versions	O
,	O
the	O
book	O
was	O
mainly	O
distributed	O
by	O
samizdat	O
photo-copying	O
.	O
</s>
<s>
The	O
source	O
code	O
for	O
the	O
original	O
V6	B-Operating_System
Unix	I-Operating_System
was	O
later	O
made	O
available	O
as	O
free	B-Application
software	I-Application
under	O
a	O
BSD	B-Operating_System
License	I-Operating_System
from	O
the	O
SCO	O
Group	O
.	O
</s>
<s>
In	O
1977	O
,	O
Richard	O
Miller	O
and	O
Ross	O
Nealon	O
,	O
working	O
under	O
the	O
supervision	O
of	O
professor	O
Juris	O
Reinfelds	O
at	O
Wollongong	O
University	O
,	O
completed	O
a	O
port	O
of	O
V6	B-Operating_System
Unix	I-Operating_System
to	O
the	O
Interdata	B-Device
7/32	I-Device
,	O
thus	O
proving	O
the	O
portability	O
of	O
Unix	B-Application
and	O
its	O
new	O
systems	O
programming	B-Language
language	I-Language
C	I-Language
in	O
practice	O
.	O
</s>
<s>
Their	O
"	O
Wollongong	O
Interdata	O
UNIX	B-Application
,	O
Level	O
6	O
"	O
also	O
included	O
utilities	O
developed	O
at	O
Wollongong	O
,	O
and	O
later	O
releases	O
had	O
features	O
of	O
V7	O
,	O
notably	O
its	O
C	B-Language
compiler	B-Language
.	O
</s>
<s>
Wollongong	O
Unix	B-Application
was	O
the	O
first	O
ever	O
port	O
to	O
a	O
platform	O
other	O
than	O
the	O
PDP	O
series	O
of	O
computers	O
,	O
proving	O
that	O
portable	O
operating	B-General_Concept
systems	I-General_Concept
were	O
indeed	O
feasible	O
,	O
and	O
that	O
C	B-Language
was	O
the	O
language	O
in	O
which	O
to	O
write	O
them	O
.	O
</s>
<s>
In	O
1980	O
,	O
this	O
version	O
was	O
licensed	O
to	O
The	B-Operating_System
Wollongong	I-Operating_System
Group	I-Operating_System
in	O
Palo	O
Alto	O
that	O
published	O
it	O
as	O
Edition	O
7	O
.	O
</s>
<s>
Around	O
the	O
same	O
time	O
,	O
a	O
Bell	O
Labs	O
port	O
to	O
the	O
Interdata	B-Device
8/32	I-Device
was	O
completed	O
,	O
but	O
not	O
externally	O
released	O
.	O
</s>
<s>
The	O
goal	O
of	O
this	O
port	O
was	O
to	O
improve	O
the	O
portability	O
of	O
Unix	B-Application
more	O
generally	O
,	O
as	O
well	O
to	O
produce	O
a	O
portable	O
version	O
of	O
the	O
C	B-Language
compiler	B-Language
.	O
</s>
<s>
The	O
resulting	O
Portable	B-Application
C	I-Application
Compiler	I-Application
(	O
PCC	O
)	O
was	O
distributed	O
with	O
V7	O
and	O
many	O
later	O
versions	O
of	O
Unix	B-Application
,	O
and	O
was	O
used	O
to	O
produce	O
the	O
UNIX/32V	B-Operating_System
port	O
to	O
the	O
VAX	B-Device
.	O
</s>
<s>
A	O
third	O
Unix	B-Application
portability	O
project	O
was	O
completed	O
at	O
Princeton	O
,	O
NJ	O
in	O
1976	O
–	O
1977	O
,	O
where	O
the	O
Unix	B-Application
kernel	O
was	O
adapted	O
to	O
run	O
as	O
a	O
guest	O
operating	O
on	O
IBM	O
's	O
VM/370	B-Application
virtualization	O
environment	O
.	O
</s>
<s>
This	O
version	O
became	O
the	O
nucleus	O
of	O
Amdahl	O
's	O
first	O
internal	O
UNIX	B-Application
offering	O
.	O
</s>
<s>
Bell	O
Labs	O
developed	O
several	O
variants	O
of	O
V6	O
,	O
including	O
the	O
stripped-down	O
MINI-UNIX	O
for	O
low-end	O
PDP-11	B-Device
models	O
,	O
LSI-UNIX	O
or	O
LSX	O
for	O
the	O
LSI-11	O
,	O
and	O
the	O
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
UNIX/RT	O
,	O
which	O
merged	O
V6	B-Operating_System
Unix	I-Operating_System
and	O
the	O
earlier	O
MERT	B-Operating_System
hypervisor	O
.	O
</s>
<s>
After	O
AT&T	O
decided	O
the	O
distribution	O
by	O
Bell	O
Labs	O
of	O
a	O
number	O
of	O
pre-V7	O
bug	O
fixes	O
would	O
constitute	O
support	O
(	O
disallowed	O
by	O
an	O
antitrust	O
settlement	O
)	O
a	O
tape	O
with	O
the	O
patchset	O
was	O
slipped	O
to	O
Lou	O
Katz	O
of	O
USENIX	B-Operating_System
,	O
who	O
distributed	O
them	O
.	O
</s>
<s>
The	O
University	O
of	O
Sydney	O
released	O
the	O
Australian	O
Unix	B-Application
Share	O
Accounting	O
Method	O
(	O
AUSAM	O
)	O
in	O
January	O
1978	O
,	O
a	O
V6	O
variant	O
with	O
improved	O
security	O
and	O
process	O
accounting	O
,	O
in	O
addition	O
to	O
the	O
fifty	O
fixes	O
that	O
leaked	O
out	O
of	O
Bell	O
Labs	O
.	O
</s>
<s>
In	O
the	O
Eastern	O
Bloc	O
,	O
clones	O
of	O
V6	B-Operating_System
Unix	I-Operating_System
appeared	O
for	O
local-built	O
PDP-11	B-Device
clones	O
(	O
MNOS	B-Operating_System
,	O
later	O
augmented	O
for	O
partial	O
compatibility	O
with	O
BSD	B-Operating_System
Unix	I-Operating_System
)	O
and	O
for	O
the	O
Elektronika	B-Device
BK	I-Device
personal	O
computer	O
(	O
BKUNIX	O
,	O
based	O
on	O
LSX	O
)	O
.	O
</s>
<s>
V6	O
was	O
used	O
for	O
teaching	O
at	O
MIT	O
in	O
2002	O
through	O
2006	O
,	O
and	O
subsequently	O
replaced	O
by	O
a	O
simpler	O
clone	O
called	O
xv6	B-Operating_System
.	O
</s>
