<s>
Multi-Environment	B-Operating_System
Real-Time	I-Operating_System
(	O
MERT	B-Operating_System
)	O
,	O
later	O
renamed	O
UNIX	B-Application
Real-Time	O
(	O
UNIX-RT	O
)	O
,	O
is	O
a	O
hybrid	O
time-sharing	B-General_Concept
and	O
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
developed	O
in	O
the	B-Operating_System
1970s	O
at	O
Bell	O
Labs	O
for	O
use	O
in	O
embedded	B-Architecture
minicomputers	B-Architecture
(	O
especially	O
PDP-11s	B-Device
)	O
.	O
</s>
<s>
A	O
version	O
named	O
Duplex	O
Multi	O
Environment	O
Real	O
Time	O
(	O
DMERT	B-Operating_System
)	O
was	O
the	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
for	O
the	B-Operating_System
AT&T	B-Device
3B20D	I-Device
telephone	O
switching	O
minicomputer	B-Architecture
,	O
designed	O
for	O
high	O
availability	O
;	O
DMERT	B-Operating_System
was	O
later	O
renamed	O
Unix	B-Operating_System
RTR	I-Operating_System
(	O
Real-Time	O
Reliable	O
)	O
.	O
</s>
<s>
A	O
generalization	O
of	O
Bell	O
Labs	O
 '	O
time-sharing	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
Unix	B-Application
,	O
</s>
<s>
MERT	B-Operating_System
featured	O
a	O
redesigned	O
,	O
modular	O
kernel	B-Operating_System
that	O
was	O
able	O
to	O
run	O
Unix	B-Application
programs	O
and	O
privileged	O
real-time	B-General_Concept
computing	I-General_Concept
processes	O
.	O
</s>
<s>
These	O
processes	O
 '	O
data	O
structures	O
were	O
isolated	O
from	O
other	O
processes	O
with	O
message	B-Architecture
passing	I-Architecture
being	O
the	B-Operating_System
preferred	O
form	O
of	O
interprocess	B-Operating_System
communication	I-Operating_System
(	O
IPC	O
)	O
,	O
although	O
shared	B-Operating_System
memory	I-Operating_System
was	O
also	O
implemented	O
.	O
</s>
<s>
MERT	B-Operating_System
also	O
had	O
a	O
custom	O
file	B-Application
system	I-Application
with	O
special	O
support	O
for	O
large	O
,	O
contiguous	O
,	O
statically	O
sized	O
files	O
,	O
as	O
used	O
in	O
real-time	O
database	O
applications	O
.	O
</s>
<s>
The	B-Operating_System
design	O
of	O
MERT	B-Operating_System
was	O
influenced	O
by	O
Dijkstra	O
's	O
THE	B-Operating_System
,	O
Hansen	O
's	O
Monitor	B-Operating_System
,	O
and	O
IBM	O
's	O
CP-67	B-Application
.	O
</s>
<s>
The	B-Operating_System
MERT	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
was	O
a	O
four-layer	O
design	O
,	O
in	O
decreasing	O
order	O
of	O
protection	B-Operating_System
:	O
</s>
<s>
The	B-Operating_System
standard	O
supervisor	O
was	O
MERT/UNIX	O
,	O
a	O
Unix	B-Application
emulator	O
with	O
an	O
extended	O
system	B-Operating_System
call	I-Operating_System
interface	O
and	O
shell	B-Application
that	O
enabled	O
the	B-Operating_System
use	O
of	O
MERT	B-Operating_System
's	O
custom	O
IPC	O
mechanisms	O
,	O
although	O
an	O
RSX-11	B-Application
emulator	O
also	O
existed	O
.	O
</s>
<s>
One	O
interesting	O
feature	O
that	O
DMERT	B-Operating_System
–	O
UNIX-RTR	B-Operating_System
introduced	O
was	O
the	B-Operating_System
notion	O
of	O
kernel	B-Operating_System
processes	O
.	O
</s>
<s>
In	O
support	O
,	O
there	O
is	O
a	O
separate	O
command	O
(	O
/bin/kpkill	O
)	O
rather	O
than	O
(	O
/bin/kill	O
)	O
,	O
that	O
is	O
used	O
to	O
send	O
signals	O
to	O
kernel	B-Operating_System
processes	O
.	O
</s>
<s>
It	O
is	O
likely	O
there	O
are	O
two	O
different	O
system	B-Operating_System
calls	I-Operating_System
also	O
(kill(2 )	O
and	O
kpkill(2 )	O
,	O
the	B-Operating_System
first	O
to	O
end	O
a	O
user	O
process	O
and	O
the	B-Operating_System
second	O
to	O
end	O
a	O
kernel	B-Operating_System
process	O
)	O
.	O
</s>
<s>
It	O
is	O
unknown	O
how	O
much	O
of	O
the	B-Operating_System
normal	O
userland	O
signaling	O
mechanism	O
is	O
in	O
place	O
in	O
/bin/kpkill	O
,	O
assuming	O
there	O
is	O
a	O
system	B-Operating_System
call	I-Operating_System
for	O
it	O
,	O
it	O
is	O
not	O
known	O
if	O
one	O
can	O
send	O
various	O
signals	O
or	O
simply	O
send	O
one	O
.	O
</s>
<s>
Also	O
unknown	O
is	O
whether	O
the	B-Operating_System
kernel	B-Operating_System
process	O
has	O
a	O
way	O
of	O
catching	O
the	B-Operating_System
signals	O
that	O
are	O
delivered	O
to	O
it	O
.	O
</s>
<s>
It	O
may	O
be	O
that	O
the	B-Operating_System
UNIX-RTR	B-Operating_System
developers	O
implemented	O
an	O
entire	O
signal	O
and	O
messaging	O
application	B-Application
programming	I-Application
interface	I-Application
(	O
API	B-Application
)	O
for	O
kernel	B-Operating_System
processes	O
.	O
</s>
<s>
If	O
one	O
has	O
root	O
on	O
a	O
UNIX-RTR	B-Operating_System
system	O
,	O
they	O
will	O
surely	O
soon	O
find	O
that	O
their	O
ls	O
-l	O
output	O
is	O
a	O
bit	O
different	O
than	O
expected	O
.	O
</s>
<s>
Namely	O
,	O
there	O
are	O
two	O
completely	O
new	O
bits	O
in	O
the	B-Operating_System
drwxr-xr-x	O
field	O
.	O
</s>
<s>
They	O
both	O
take	O
place	O
in	O
the	B-Operating_System
first	O
column	O
,	O
and	O
are	O
C	B-Language
(	O
contiguous	O
)	O
and	O
x	O
(	O
extents	B-Application
)	O
.	O
</s>
<s>
Both	O
of	O
these	O
have	O
to	O
do	O
with	O
contiguous	O
data	O
,	O
however	O
one	O
may	O
be	O
to	O
do	O
with	O
inodes	B-Application
and	O
the	B-Operating_System
other	O
with	O
non-metadata	O
.	O
</s>
<s>
AT&T	O
,	O
then	O
Lucent	O
,	O
and	O
now	O
Alcatel-Lucent	O
,	O
are	O
the	B-Operating_System
vendor	O
of	O
the	B-Operating_System
SPARC-based	O
and	O
Solaris-OEM	O
package	O
ATT3bem	O
(	O
which	O
lives	O
on	O
Solaris	B-Application
SPARC	B-Architecture
in	O
/opt/ATT3bem	O
)	O
.	O
</s>
<s>
This	O
is	O
a	O
full	O
3B21D	B-Device
emulator	O
(	O
known	O
as	O
the	B-Operating_System
3B21E	O
,	O
the	B-Operating_System
system	O
behind	O
the	B-Operating_System
Very	O
Compact	O
Digital	O
eXchange	O
,	O
or	O
VCDX	O
)	O
which	O
is	O
meant	O
to	O
provide	O
a	O
production	O
environment	O
to	O
the	B-Operating_System
Administrative	O
Module	O
(	O
AM	O
)	O
portion	O
of	O
the	B-Operating_System
5ESS	B-Device
switch	I-Device
.	O
</s>
<s>
There	O
are	O
parts	O
of	O
the	B-Operating_System
5ESS	B-Device
that	O
are	O
not	O
part	O
of	O
the	B-Operating_System
3B21D	B-Device
microcomputer	O
at	O
all	O
:	O
SMs	O
and	O
CMs	O
.	O
</s>
<s>
Under	O
the	B-Operating_System
emulator	O
the	B-Operating_System
workstation	O
is	O
referred	O
to	O
as	O
the	B-Operating_System
'	O
AW	O
 '	O
(	O
Administrative	O
Workstation	O
)	O
.	O
</s>
<s>
The	B-Operating_System
emulator	O
installs	O
with	O
Solaris	B-Application
2.6/SPARC	O
and	O
also	O
comes	O
with	O
Solstice	O
X.25	B-Protocol
9.1	O
(	O
SUNWconn	O
)	O
,	O
formerly	O
known	O
as	O
SunLink	O
X.25	B-Protocol
.	O
</s>
<s>
The	B-Operating_System
reason	O
for	O
packaging	O
the	B-Operating_System
X.25	B-Protocol
stack	O
with	O
the	B-Operating_System
3B21D	B-Device
emulator	O
is	O
because	O
the	B-Operating_System
Bell	O
System	O
,	O
regional	O
Bell	O
operating	O
companies	O
,	O
and	O
ILECs	O
still	O
use	O
X.25	B-Protocol
networks	O
for	O
their	O
most	O
critical	O
of	O
systems	O
(	O
telephone	O
switches	O
may	O
live	O
on	O
X.25	B-Protocol
or	O
Datakit	O
VCS	O
II	O
,	O
a	O
similar	O
network	O
developed	O
at	O
Bell	O
Labs	O
,	O
but	O
they	O
do	O
not	O
have	O
TCP/IP	O
stacks	O
)	O
.	O
</s>
<s>
The	B-Operating_System
AT&	O
T/Alcatel	O
-Lucent	O
emulator	O
is	O
not	O
an	O
easy	O
program	O
to	O
get	O
working	O
correctly	O
,	O
even	O
if	O
one	O
manages	O
to	O
have	O
an	O
image	O
from	O
a	O
pulled	O
working	O
5ESS	B-Device
hard	O
disk	O
'	O
dd	O
 '	O
output	O
file	O
.	O
</s>
<s>
First	O
,	O
there	O
are	O
quite	O
a	O
few	O
bugs	O
the	B-Operating_System
user	O
must	O
navigate	O
around	O
in	O
the	B-Operating_System
installation	O
process	O
.	O
</s>
<s>
But	O
there	O
is	O
scant	O
documentation	O
on	O
the	B-Operating_System
CD	O
which	O
describes	O
this	O
.	O
</s>
<s>
The	B-Operating_System
name	O
of	O
this	O
file	O
is	O
em_devmap	O
for	O
SS5s	O
,	O
and	O
em_devmap.ultra	O
for	O
Ultra60s	O
.	O
</s>
<s>
In	O
addition	O
,	O
one	O
of	O
the	B-Operating_System
bugs	O
mentioned	O
in	O
the	B-Operating_System
install	O
process	O
is	O
a	O
broken	O
script	O
to	O
fdisk	O
and	O
image	O
hard	O
disks	O
correctly	O
:	O
certain	O
things	O
need	O
to	O
be	O
written	O
to	O
certain	O
offsets	O
,	O
because	O
the	B-Operating_System
/opt/ATT3bem/bin/3bem	O
process	O
expects	O
,	O
or	O
seems	O
to	O
need	O
,	O
these	O
hard-coded	O
locations	O
.	O
</s>
<s>
The	B-Operating_System
emulator	O
runs	O
on	O
SPARCstation-5s	O
and	O
UltraSPARC-60s	O
.	O
</s>
<s>
It	O
is	O
likely	O
that	O
the	B-Operating_System
3B21D	B-Device
is	O
emulated	O
faster	O
on	O
a	O
modern	O
SPARC	B-Architecture
than	O
a	O
3B21D	B-Device
microcomputer	O
's	O
processor	O
actually	O
runs	O
as	O
measured	O
in	O
MIPS	O
.	O
</s>
<s>
The	B-Operating_System
most	O
difficult	O
thing	O
about	O
having	O
the	B-Operating_System
emulator	O
is	O
acquiring	O
a	O
DMERT/UNIX	O
-RTR	O
hdd	O
image	O
to	O
actually	O
run	O
.	O
</s>
<s>
The	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
for	O
the	B-Operating_System
5ESS	B-Device
is	O
restricted	O
to	O
a	O
few	O
people	O
,	O
employees	O
and	O
customers	O
of	O
the	B-Operating_System
vendor	O
,	O
who	O
either	O
work	O
on	O
it	O
or	O
write	O
the	B-Operating_System
code	O
for	O
it	O
.	O
</s>
<s>
Having	O
an	O
image	O
of	O
a	O
running	O
system	O
,	O
which	O
can	O
be	O
obtained	O
on	O
eBay	O
,	O
pulled	O
from	O
a	O
working	O
3B21D	B-Device
,	O
and	O
imaged	O
to	O
a	O
file	O
or	O
put	O
into	O
an	O
Ultra60	O
or	O
SPARCstation-5	O
,	O
provides	O
the	B-Operating_System
resources	O
to	O
attempt	O
to	O
run	O
the	B-Operating_System
UNIX-RTR	B-Operating_System
system	O
.	O
</s>
<s>
The	B-Operating_System
uname	O
-a	O
output	O
of	O
the	B-Operating_System
Bourne	O
shell	B-Application
running	O
UNIX-RTR	B-Operating_System
(	O
Real-time	O
Reliable	O
)	O
is	O
:	O
</s>
<s>
Though	O
on	O
3B20D	O
systems	O
it	O
will	O
print	O
20	O
instead	O
of	O
21	O
,	O
though	O
3B20Ds	O
are	O
rare	O
,	O
nowadays	O
most	O
non-VCDX	O
5ESSs	O
are	O
3B21D	B-Device
hardware	O
,	O
not	O
3B20D	O
(	O
although	O
they	O
will	O
run	O
the	B-Operating_System
software	O
fine	O
)	O
.	O
</s>
<s>
The	B-Operating_System
3B20D	O
uses	O
the	B-Operating_System
WE32000	B-General_Concept
processor	O
while	O
the	B-Operating_System
21	O
uses	O
the	B-Operating_System
WE32100	O
.	O
</s>
<s>
One	O
thing	O
unusual	O
about	O
the	B-Operating_System
processor	O
is	O
the	B-Operating_System
direction	O
the	B-Operating_System
stack	O
grows	O
:	O
up	O
.	O
</s>
<s>
UNIX-RTR	B-Operating_System
includes	O
an	O
atomic	O
file	O
swap	O
command	O
(	O
atomsw	O
,	O
manual	O
page	O
below	O
)	O
:	O
</s>
