<s>
The	O
Network	B-Operating_System
Livermore	I-Operating_System
Timesharing	I-Operating_System
System	I-Operating_System
(	O
NLTSS	B-Operating_System
,	O
also	O
sometimes	O
the	O
New	B-Operating_System
Livermore	I-Operating_System
Time	I-Operating_System
Sharing	I-Operating_System
System	I-Operating_System
)	O
is	O
an	O
operating	B-General_Concept
system	I-General_Concept
that	O
was	O
actively	O
developed	O
at	O
Lawrence	O
Livermore	O
Laboratory	O
(	O
now	O
Lawrence	O
Livermore	O
National	O
Laboratory	O
)	O
from	O
1979	O
until	O
about	O
1988	O
,	O
though	O
it	O
continued	O
to	O
run	O
production	O
applications	O
until	O
1995	O
.	O
</s>
<s>
An	O
earlier	O
system	O
,	O
the	O
Livermore	B-Operating_System
Time	I-Operating_System
Sharing	I-Operating_System
System	I-Operating_System
had	O
been	O
developed	O
over	O
a	O
decade	O
earlier	O
.	O
</s>
<s>
NLTSS	B-Operating_System
ran	O
initially	O
on	O
a	O
CDC	B-Device
7600	I-Device
computer	O
,	O
but	O
only	O
ran	O
production	O
from	O
about	O
1985	O
until	O
1994	O
on	O
Cray	O
computers	O
including	O
the	O
Cray-1	B-Device
,	O
Cray	B-Device
X-MP	I-Device
,	O
and	O
Cray	B-Device
Y-MP	I-Device
models	O
.	O
</s>
<s>
The	O
NLTSS	B-Operating_System
operating	B-General_Concept
system	I-General_Concept
was	O
unusual	O
in	O
many	O
respects	O
and	O
unique	O
in	O
some	O
.	O
</s>
<s>
NLTSS	B-Operating_System
was	O
a	O
microkernel	B-Operating_System
message	B-Architecture
passing	I-Architecture
system	O
.	O
</s>
<s>
That	O
system	O
call	O
,	O
which	O
might	O
be	O
called	O
"	O
communicate	O
"	O
(	O
it	O
did	O
n't	O
have	O
a	O
name	O
because	O
it	O
did	O
n't	O
need	O
to	O
be	O
distinguished	O
from	O
other	O
system	O
calls	O
)	O
accepted	O
a	O
list	O
of	O
"	O
buffer	O
tables	O
"	O
(	O
e.g.	O
,	O
see	O
The	O
NLTSS	B-Operating_System
Message	O
System	O
Interface	O
)	O
that	O
contained	O
control	O
information	O
for	O
message	O
communication	O
–	O
either	O
sends	O
or	O
receives	O
.	O
</s>
<s>
Such	O
communication	O
,	O
both	O
locally	O
within	O
the	O
system	O
and	O
across	O
a	O
network	O
was	O
all	O
the	O
kernel	O
of	O
the	O
system	O
supported	O
directly	O
for	O
user	O
processes	B-Operating_System
.	O
</s>
<s>
The	O
"	O
message	O
system	O
"	O
(	O
supporting	O
the	O
one	O
call	O
and	O
the	O
network	B-Architecture
protocols	I-Architecture
)	O
and	O
drivers	O
for	O
the	O
disks	O
and	O
processor	O
composed	O
the	O
entire	O
kernel	O
of	O
the	O
system	O
.	O
</s>
<s>
NLTSS	B-Operating_System
is	O
a	O
capability-based	O
security	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
system	O
.	O
</s>
<s>
The	O
file	O
server	O
was	O
a	O
process	O
privileged	O
to	O
be	O
trusted	O
by	O
the	O
drivers	O
for	O
local	O
storage	O
(	O
disk	O
storage	O
,	O
)	O
and	O
the	O
process	O
server	O
was	O
a	O
process	O
privileged	O
to	O
be	O
trusted	O
by	O
the	O
processor	O
driver	O
(	O
software	O
that	O
switched	O
time	B-General_Concept
sharing	I-General_Concept
control	O
between	O
processes	B-Operating_System
in	O
the	O
"	O
alternator	O
"	O
,	O
handled	O
interrupts	O
for	O
processes	B-Operating_System
besides	O
the	O
"	O
communicate	O
"	O
call	O
,	O
provided	O
access	O
to	O
memory	O
and	O
process	O
state	O
for	O
the	O
process	O
server	O
,	O
etc	O
.	O
</s>
<s>
NLTSS	B-Operating_System
was	O
a	O
true	O
network	B-Protocol
operating	I-Protocol
system	I-Protocol
in	O
that	O
its	O
resource	O
requests	O
could	O
come	O
from	O
local	O
processes	B-Operating_System
or	O
remote	O
processes	B-Operating_System
anywhere	O
on	O
the	O
network	O
and	O
the	O
servers	O
did	O
n't	O
distinguish	O
them	O
.	O
</s>
<s>
Communication	O
between	O
processes	B-Operating_System
in	O
NLTSS	B-Operating_System
by	O
convention	O
used	O
the	O
Livermore	O
Interactive	O
Network	O
Communication	O
System	O
(	O
LINCS	O
)	O
protocol	B-Protocol
suite	I-Protocol
,	O
which	O
defined	O
a	O
protocol	B-Protocol
stack	I-Protocol
along	O
the	O
lines	O
of	O
that	O
defined	O
by	O
the	O
OSI	O
reference	O
model	O
.	O
</s>
<s>
The	O
transport	O
level	O
protocol	O
for	O
NLTSS	B-Operating_System
and	O
LINCS	O
was	O
named	O
Delta-T	O
.	O
At	O
the	O
presentation	O
level	O
,	O
LINCS	O
defined	O
standards	O
for	O
communicating	O
numbered	O
parameters	O
as	O
tokens	O
(	O
e.g.	O
,	O
integers	O
,	O
capabilities	O
,	O
etc	O
.	O
)	O
</s>
<s>
that	O
were	O
stored	O
in	O
a	O
session	O
level	O
record	O
for	O
processing	O
in	O
a	O
remote	B-Operating_System
procedure	I-Operating_System
call	I-Operating_System
sort	O
of	O
mechanism	O
.	O
</s>
<s>
The	O
notion	O
of	O
a	O
"	O
user	O
"	O
was	O
only	O
rather	O
peripherally	O
defined	O
in	O
NLTSS	B-Operating_System
.	O
</s>
<s>
There	O
was	O
an	O
"	O
account	O
server	O
"	O
that	O
kept	O
track	O
of	O
which	O
users	O
were	O
using	O
which	O
resources	O
(	O
e.g.	O
,	O
requests	O
to	O
create	O
objects	O
such	O
as	O
file	O
or	O
processes	B-Operating_System
required	O
such	O
an	O
account	O
capability	B-General_Concept
)	O
.	O
</s>
<s>
Any	O
process	O
could	O
make	O
requests	O
to	O
the	O
file	O
server	O
for	O
the	O
creation	O
of	O
files	O
(	O
returning	O
a	O
file	O
capability	B-General_Concept
)	O
,	O
ask	O
to	O
read	O
or	O
write	O
files	O
(	O
by	O
presenting	O
a	O
file	O
capability	B-General_Concept
)	O
,	O
etc	O
.	O
</s>
<s>
A	O
library	O
call	O
to	O
read	O
a	O
file	O
would	O
typically	O
block	O
until	O
the	O
control	O
reply	O
was	O
received	O
from	O
the	O
file	O
server	O
,	O
though	O
asynchronous	B-Architecture
I/O	I-Architecture
would	O
of	O
course	O
not	O
block	O
and	O
could	O
check	O
or	O
block	O
later	O
.	O
</s>
<s>
In	O
NLTSS	B-Operating_System
the	O
process	O
server	O
was	O
quite	O
similar	O
to	O
the	O
file	O
server	O
in	O
that	O
user	O
processes	B-Operating_System
could	O
ask	O
for	O
the	O
creation	O
of	O
processes	B-Operating_System
,	O
the	O
starting	O
or	O
stopping	O
of	O
processes	B-Operating_System
,	O
reading	O
or	O
writing	O
process	O
memory	O
or	O
registers	O
,	O
and	O
to	O
be	O
notified	O
of	O
process	O
faults	O
.	O
</s>
<s>
The	O
process	O
server	O
was	O
an	O
ordinary	O
user	B-Operating_System
mode	I-Operating_System
process	O
that	O
was	O
simply	O
trusted	O
to	O
communicate	O
with	O
the	O
CPU	B-Device
driver	O
,	O
just	O
like	O
the	O
file	O
server	O
was	O
trusted	O
to	O
communicate	O
with	O
the	O
disk	O
driver	O
.	O
</s>
<s>
An	O
example	O
higher	O
level	O
server	O
in	O
NLTSS	B-Operating_System
was	O
the	O
directory	O
server	O
.	O
</s>
<s>
Since	O
capabilities	O
were	O
simply	O
data	O
this	O
was	O
n't	O
a	O
particularly	O
difficult	O
task	O
,	O
consisting	O
mostly	O
of	O
manipulating	O
access	O
permissions	O
on	O
the	O
capabilities	O
according	O
to	O
the	O
conventions	O
defined	O
in	O
the	O
LINCS	O
protocol	B-Protocol
suite	I-Protocol
.	O
</s>
<s>
If	O
this	O
bit	O
was	O
turned	O
off	O
(	O
disallowed	O
)	O
,	O
then	O
any	O
permissions	O
turned	O
off	O
in	O
the	O
directory	O
capability	B-General_Concept
were	O
in	O
turn	O
turned	O
off	O
in	O
the	O
capability	B-General_Concept
being	O
fetched	O
before	O
it	O
was	O
returned	O
to	O
the	O
requesting	O
application	O
.	O
</s>
<s>
The	O
bulk	O
of	O
the	O
programming	O
for	O
NLTSS	B-Operating_System
was	O
done	O
in	O
a	O
Pascal	B-Application
extension	O
developed	O
at	O
Los	O
Alamos	O
National	O
Laboratory	O
known	O
as	O
"	O
Model	O
"	O
.	O
</s>
<s>
Model	O
extended	O
Pascal	B-Application
to	O
include	O
an	O
abstract	O
data	O
type	O
(	O
object	O
)	O
mechanism	O
and	O
some	O
other	O
features	O
.	O
</s>
<s>
NLTSS	B-Operating_System
was	O
saddled	O
with	O
a	O
compatibility	O
legacy	O
.	O
</s>
<s>
NLTSS	B-Operating_System
followed	O
the	O
development	O
and	O
deployment	O
of	O
the	O
Livermore	B-Operating_System
Time	I-Operating_System
Sharing	I-Operating_System
System	I-Operating_System
(	O
LTSS	O
)	O
in	O
the	O
Livermore	O
Computer	O
Center	O
at	O
LLNL	O
(	O
~	O
1968	O
–	O
1988	O
?	O
)	O
.	O
</s>
<s>
NLTSS	B-Operating_System
development	O
began	O
about	O
the	O
same	O
time	O
LTSS	O
was	O
ported	O
to	O
the	O
Cray-1	B-Device
to	O
become	O
the	O
Cray	B-Operating_System
Time	I-Operating_System
Sharing	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
To	O
stay	O
backward	B-General_Concept
compatible	I-General_Concept
with	O
the	O
many	O
scientific	O
applications	O
at	O
LLNL	O
,	O
NLTSS	B-Operating_System
was	O
forced	O
to	O
emulate	O
the	O
prior	O
LTSS	O
operating	B-General_Concept
system	I-General_Concept
's	O
system	O
calls	O
.	O
</s>
<s>
As	O
one	O
example	O
,	O
while	O
the	O
directory	O
structure	O
and	O
thus	O
the	O
process	O
structure	O
for	O
NLTSS	B-Operating_System
was	O
naturally	O
a	O
directed	O
graph	O
(	O
process	O
capabilities	O
could	O
be	O
stored	O
in	O
directories	O
just	O
like	O
file	O
capabilities	O
or	O
directory	O
capabilities	O
)	O
,	O
the	O
baselib	O
library	O
emulated	O
a	O
simple	O
linear	O
(	O
controller	O
–	O
controllee	O
)	O
process	O
structure	O
(	O
not	O
even	O
a	O
tree	B-Data_Structure
structure	I-Data_Structure
as	O
in	O
Unix	B-Application
)	O
to	O
stay	O
compatible	O
with	O
the	O
prior	O
LTSS	O
.	O
</s>
<s>
Since	O
scientific	O
users	O
never	O
accessed	O
NLTSS	B-Operating_System
services	O
outside	O
the	O
baselib	O
library	O
,	O
NLTSS	B-Operating_System
ended	O
up	O
looking	O
nearly	O
exactly	O
like	O
LTSS	O
to	O
its	O
users	O
.	O
</s>
<s>
Most	O
users	O
were	O
n't	O
aware	O
of	O
capabilities	O
,	O
did	O
n't	O
realize	O
that	O
they	O
could	O
access	O
resources	O
across	O
the	O
network	O
,	O
and	O
generally	O
were	O
n't	O
aware	O
that	O
NLTSS	B-Operating_System
offered	O
any	O
services	O
beyond	O
those	O
of	O
LTSS	O
.	O
</s>
<s>
NLTSS	B-Operating_System
did	O
support	O
shared	B-Operating_System
memory	I-Operating_System
symmetric	B-Operating_System
multiprocessing	I-Operating_System
,	O
a	O
development	O
that	O
paralleled	O
a	O
similar	O
development	O
in	O
the	O
Cray	B-Operating_System
Time	I-Operating_System
Sharing	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
Even	O
the	O
name	O
NLTSS	B-Operating_System
was	O
something	O
of	O
a	O
legacy	O
.	O
</s>
<s>
The	O
"	O
New	B-Operating_System
Livermore	I-Operating_System
Time	I-Operating_System
Sharing	I-Operating_System
System	I-Operating_System
"	O
name	O
was	O
initially	O
considered	O
a	O
temporary	O
name	O
to	O
use	O
during	O
development	O
.	O
</s>
<s>
Once	O
the	O
system	O
began	O
to	O
run	O
some	O
applications	O
in	O
a	O
dual	O
system	O
mode	O
(	O
sort	O
of	O
a	O
virtual	B-Architecture
machine	I-Architecture
sharing	O
drivers	O
with	O
LTSS	O
)	O
a	O
more	O
permanent	O
name	O
,	O
LIncs	O
Network	B-Protocol
Operating	I-Protocol
System	I-Protocol
(	O
LINOS	O
)	O
,	O
was	O
chosen	O
by	O
the	O
developers	O
.	O
</s>
<s>
Unfortunately	O
,	O
the	O
management	O
at	O
LLNL	O
decided	O
that	O
the	O
name	O
could	O
n't	O
be	O
changed	O
at	O
that	O
point	O
(	O
seemingly	O
because	O
the	O
prior	O
term	O
had	O
been	O
used	O
in	O
budget	O
requests	O
)	O
so	O
the	O
temporary	O
development	O
NLTSS	B-Operating_System
name	O
stayed	O
with	O
the	O
system	O
throughout	O
its	O
lifetime	O
.	O
</s>
<s>
A	O
mass	B-Device
storage	I-Device
system	O
was	O
also	O
developed	O
in	O
parallel	O
with	O
NLTSS	B-Operating_System
that	O
used	O
the	O
LINCS	O
protocols	O
(	O
same	O
file	O
and	O
directory	O
protocols	O
as	O
NLTSS	B-Operating_System
)	O
.	O
</s>
<s>
Unitree	O
was	O
generally	O
superseded	O
by	O
the	O
High	B-Application
Performance	I-Application
Storage	I-Application
System	I-Application
(	O
HPSS	O
)	O
that	O
could	O
loosely	O
be	O
considered	O
a	O
legacy	O
of	O
LINCS	O
and	O
NLTSS	B-Operating_System
.	O
</s>
<s>
For	O
example	O
,	O
LINCS	O
and	O
NLTSS	B-Operating_System
introduced	O
a	O
form	O
of	O
third	O
party	O
transfer	O
(	O
to	O
copy	O
file	O
to	O
file	O
in	O
NLTSS	B-Operating_System
a	O
process	O
could	O
send	O
two	O
requests	O
to	O
file	O
servers	O
,	O
one	O
to	O
read	O
and	O
one	O
to	O
write	O
and	O
direct	O
the	O
file	O
servers	O
to	O
transfer	O
the	O
data	O
between	O
themselves	O
)	O
that	O
carried	O
through	O
in	O
modified	O
form	O
to	O
Unitree	O
and	O
HPSS	O
.	O
</s>
<s>
The	O
biggest	O
knock	O
against	O
NLTSS	B-Operating_System
during	O
its	O
production	O
lifetime	O
was	O
performance	O
.	O
</s>
<s>
This	O
generally	O
was	O
n't	O
a	O
significant	O
problem	O
for	O
disk	O
input/output	B-General_Concept
(	O
I/O	B-General_Concept
)	O
,	O
but	O
the	O
systems	O
that	O
NLTSS	B-Operating_System
ran	O
on	O
also	O
supported	O
a	O
significant	O
complement	O
of	O
very	O
low	O
latency	O
solid	B-Device
state	I-Device
disks	I-Device
with	O
access	O
times	O
under	O
10	O
microseconds	O
.	O
</s>
<s>
The	O
initial	O
latencies	O
for	O
file	O
operations	O
under	O
NLTSS	B-Operating_System
were	O
comparable	O
to	O
the	O
latency	O
for	O
solid	B-Device
state	I-Device
disk	I-Device
access	O
and	O
significantly	O
higher	O
than	O
the	O
LTSS	O
latency	O
for	O
such	O
access	O
.	O
</s>
<s>
To	O
improve	O
file	O
access	O
latency	O
under	O
NLTSS	B-Operating_System
the	O
implementation	O
was	O
changed	O
significantly	O
to	O
put	O
the	O
most	O
latency	O
sensitive	O
processes	B-Operating_System
(	O
in	O
particular	O
the	O
file	O
server	O
)	O
"	O
in	O
the	O
kernel	O
"	O
.	O
</s>
<s>
This	O
effort	O
was	O
n't	O
as	O
significant	O
as	O
it	O
might	O
at	O
first	O
sound	O
as	O
all	O
NLTSS	B-Operating_System
servers	O
worked	O
on	O
a	O
multithreading	B-Operating_System
model	O
.	O
</s>
<s>
What	O
this	O
change	O
really	O
amounted	O
to	O
was	O
to	O
move	O
the	O
threads	B-Operating_System
responsible	O
for	O
file	O
server	O
services	O
from	O
a	O
separate	O
file	O
server	O
process	O
into	O
the	O
kernel	O
"	O
process	O
"	O
.	O
</s>
<s>
)	O
,	O
but	O
file	O
operations	O
avoided	O
some	O
significant	O
context	O
changes	O
that	O
were	O
the	O
primary	O
cause	O
of	O
the	O
higher	O
latencies	O
over	O
what	O
the	O
older	O
LTSS	O
and	O
the	O
competing	O
Cray	B-Operating_System
Time	I-Operating_System
Sharing	I-Operating_System
System	I-Operating_System
provided	O
.	O
</s>
<s>
This	O
change	O
did	O
significantly	O
(	O
~	O
3x	O
)	O
improve	O
the	O
latency	O
of	O
file	O
I/O	B-General_Concept
operations	I-General_Concept
,	O
but	O
it	O
also	O
meant	O
that	O
the	O
file	O
server	O
became	O
a	O
trusted	O
part	O
of	O
the	O
kernel	O
(	O
by	O
implementation	O
,	O
not	O
by	O
design	O
)	O
.	O
</s>
<s>
A	O
second	O
implementation	O
issue	O
with	O
NLTSS	B-Operating_System
related	O
to	O
the	O
security/integrity	O
of	O
its	O
capability	B-General_Concept
as	O
data	O
implementation	O
.	O
</s>
<s>
This	O
implementation	O
used	O
a	O
password	O
capability	B-General_Concept
model	O
(	O
e.g.	O
,	O
see	O
Control	O
by	O
Password	O
)	O
.	O
</s>
<s>
With	O
this	O
model	O
any	O
person	O
or	O
process	O
that	O
could	O
get	O
access	O
to	O
the	O
memory	O
space	O
of	O
a	O
process	O
would	O
have	O
the	O
authority	O
to	O
access	O
the	O
capability	B-General_Concept
represented	O
by	O
the	O
data	O
found	O
in	O
that	O
memory	O
.	O
</s>
<s>
Some	O
system	O
architects	O
(	O
e.g.	O
,	O
Andrew	O
S	O
.	O
Tanenbaum	O
,	O
the	O
architect	O
of	O
the	O
Amoeba	B-Operating_System
distributed	I-Operating_System
operating	I-Operating_System
system	I-Operating_System
)	O
have	O
suggested	O
that	O
this	O
property	O
of	O
access	O
to	O
memory	O
implying	O
access	O
to	O
capabilities	O
is	O
not	O
an	O
inherent	O
problem	O
.	O
</s>
<s>
In	O
the	O
environment	O
of	O
NLTSS	B-Operating_System
,	O
it	O
sometimes	O
happened	O
that	O
people	O
took	O
program	O
memory	B-Error_Name
dumps	I-Error_Name
to	O
others	O
for	O
analysis	O
.	O
</s>
<s>
Because	O
of	O
this	O
and	O
other	O
concerns	O
,	O
such	O
password	O
capabilities	O
were	O
considered	O
a	O
vulnerability	O
in	O
NLTSS	B-Operating_System
.	O
</s>
<s>
This	O
mechanism	O
was	O
n't	O
put	O
into	O
production	O
in	O
NLTSS	B-Operating_System
both	O
because	O
of	O
its	O
significant	O
performance	O
cost	O
and	O
because	O
users	O
were	O
n't	O
aware	O
of	O
the	O
vulnerability	O
from	O
password	O
capabilities	O
.	O
</s>
<s>
A	O
design	O
issue	O
with	O
NLTSS	B-Operating_System
that	O
was	O
n't	O
considered	O
until	O
years	O
after	O
it	O
was	O
removed	O
from	O
production	O
was	O
its	O
open	O
network	O
architecture	O
.	O
</s>
<s>
In	O
NLTSS	B-Operating_System
processes	B-Operating_System
were	O
considered	O
as	O
virtual	O
processors	O
in	O
a	O
network	O
with	O
no	O
firewalls	B-Application
or	O
other	O
restrictions	O
.	O
</s>
<s>
To	O
correct	O
this	O
problem	O
NLTSS	B-Operating_System
would	O
have	O
to	O
require	O
capabilities	O
to	O
enable	O
communication	O
.	O
</s>
<s>
Late	O
development	O
work	O
on	O
NLTSS	B-Operating_System
such	O
as	O
"	O
stream	O
numbers	O
"	O
was	O
getting	O
close	O
to	O
such	O
a	O
facility	O
,	O
but	O
by	O
the	O
time	O
active	O
development	O
stopped	O
in	O
1988	O
,	O
communication	O
in	O
NLTSS	B-Operating_System
was	O
still	O
unconfined	O
.	O
</s>
