<s>
TSX-Plus	B-Device
is	O
a	O
multi-user	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
for	O
the	O
PDP-11/LSI	O
-11	O
series	O
of	O
computers	O
.	O
</s>
<s>
It	O
was	O
developed	O
by	O
S&H	O
Computer	O
Systems	O
,	O
Inc	O
.	O
and	O
is	O
based	O
on	O
DEC	O
's	O
RT-11	B-Operating_System
single-user	B-Operating_System
real-time	B-Operating_System
operating	I-Operating_System
system	I-Operating_System
(	O
TSX-Plus	B-Device
installs	O
on	O
top	O
of	O
RT-11	B-Operating_System
)	O
.	O
</s>
<s>
Due	O
to	O
the	O
constraints	O
of	O
the	O
memory	O
management	O
system	O
in	O
the	O
PDP-11/LSI	O
-11	O
,	O
the	O
entire	O
operating	B-General_Concept
system	I-General_Concept
core	O
must	O
occupy	O
no	O
more	O
than	O
40	O
kibibytes	O
of	O
memory	O
,	O
out	O
of	O
a	O
maximum	O
possible	O
4	O
mebibytes	O
of	O
physical	O
memory	O
that	O
can	O
actually	O
be	O
installed	O
in	O
those	O
machines	O
(	O
mandated	O
by	O
the	O
22-bit	O
address	B-General_Concept
space	I-General_Concept
)	O
.	O
</s>
<s>
The	O
strength	O
of	O
TSX-Plus	B-Device
is	O
to	O
simultaneously	O
provide	O
to	O
multiple	B-Operating_System
users	I-Operating_System
the	O
services	O
of	O
DEC	O
's	O
single-user	B-Operating_System
RT-11	B-Operating_System
.	O
</s>
<s>
Depending	O
on	O
which	O
PDP-11	B-Device
model	O
and	O
the	O
amount	O
of	O
memory	O
,	O
the	O
system	O
could	O
support	O
a	O
minimum	O
of	O
12	O
users	O
(	O
14-18	O
users	O
on	O
a	O
2Mb	O
11/73	O
,	O
depending	O
on	O
workload	O
)	O
.	O
</s>
<s>
A	O
productivity	O
feature	O
called	O
"	O
virtual	O
lines	O
"	O
"	O
allows	O
a	O
single	B-Operating_System
user	I-Operating_System
to	O
control	O
several	O
tasks	O
from	O
a	O
single	O
terminal.	O
"	O
</s>
<s>
Released	O
in	O
1980	O
,	O
TSX-Plus	B-Device
was	O
the	O
successor	O
to	O
TSX	O
,	O
released	O
in	O
1976	O
.	O
</s>
<s>
The	O
last	O
version	O
of	O
TSX-Plus	B-Device
had	O
TCP/IP	B-Protocol
support	O
.	O
</s>
<s>
TSX-Plus	B-Device
required	O
bootstrapping	O
RT-11	B-Operating_System
first	O
before	O
running	O
TSX-Plus	B-Device
as	O
a	O
user	O
program	O
.	O
</s>
<s>
Once	O
TSX-Plus	B-Device
was	O
running	O
,	O
it	O
would	O
take	O
over	O
complete	O
control	O
of	O
the	O
machine	O
from	O
RT-11	B-Operating_System
.	O
</s>
<s>
It	O
provided	O
true	O
memory	O
protection	O
for	O
users	O
from	O
other	O
users	O
,	O
provided	O
user	O
accounts	O
and	O
maintained	O
account	O
separation	O
on	O
disk	O
volumes	O
and	O
implemented	O
a	O
superset	O
of	O
the	O
RT-11	B-Operating_System
EMT	O
programmed	O
requests	O
.	O
</s>
<s>
RT-11	B-Operating_System
programs	O
generally	O
ran	O
,	O
unmodified	O
,	O
under	O
TSX-Plus	B-Device
and	O
,	O
in	O
fact	O
,	O
most	O
of	O
the	O
RT-11	B-Operating_System
utilities	O
were	O
used	O
as-is	O
under	O
TSX-Plus	B-Device
.	O
</s>
