<s>
MTS	B-Operating_System
System	I-Operating_System
Architecture	I-Operating_System
describes	O
the	O
software	O
organization	O
of	O
the	O
Michigan	B-Application
Terminal	I-Application
System	I-Application
,	O
a	O
time-sharing	B-General_Concept
computer	B-General_Concept
operating	I-General_Concept
system	I-General_Concept
in	O
use	O
from	O
1967	O
to	O
1999	O
on	O
IBM	B-Device
S/360	I-Device
-67	I-Device
,	O
IBM	B-Device
System/370	I-Device
,	O
and	O
compatible	O
computers	O
.	O
</s>
<s>
+	O
MTS	O
ArchitectureMTS	O
Lecture	O
1	O
,	O
a	O
transcription	O
of	O
the	O
first	O
in	O
a	O
series	O
of	O
lectures	O
on	O
the	O
internals	O
of	O
the	O
Michigan	B-Application
Terminal	I-Application
System	I-Application
given	O
by	O
Mike	O
Alexander	O
,	O
Don	O
Boettner	O
,	O
Jim	O
Hamilton	O
,	O
and	O
Doug	O
Smith	O
,	O
c	O
.	O
1972	O
StateMode	O
"	O
The	O
Protection	O
of	O
Information	O
in	O
a	O
General	O
Purpose	O
Time-Sharing	B-General_Concept
Environment	O
"	O
,	O
Gary	O
C	O
.	O
Pirkola	O
and	O
John	O
Sanguinetti	O
,	O
Proceedings	O
of	O
the	O
IEEE	O
Symposium	O
on	O
Trends	O
and	O
Applications	O
1977	O
:	O
Computer	O
Security	O
and	O
Integrity	O
,	O
vol	O
.	O
</s>
<s>
The	O
University	O
of	O
Michigan	O
Multi-Programming	O
Supervisor	B-Operating_System
(	O
UMMPS	O
)	O
,	O
has	O
complete	O
control	O
of	O
the	O
hardware	O
and	O
manages	O
a	O
collection	O
of	O
job	O
programs	O
.	O
</s>
<s>
The	O
interface	O
with	O
the	O
supervisor	B-Operating_System
is	O
the	O
same	O
for	O
all	O
components	O
and	O
very	O
few	O
special	O
cases	O
are	O
allowed	O
;	O
for	O
example	O
,	O
all	O
input/output	O
operations	O
are	O
done	O
using	O
the	O
same	O
supervisor	B-Operating_System
facilities	O
whether	O
the	O
input/output	O
is	O
for	O
a	O
card	O
reader	O
,	O
a	O
paging	O
device	O
,	O
or	O
any	O
other	O
device	O
.	O
</s>
<s>
Most	O
access	O
to	O
supervisor	B-Operating_System
services	O
is	O
via	O
system	O
subroutines	O
that	O
issue	O
the	O
necessary	O
Supervisor	B-Operating_System
Call	I-Operating_System
instructions	I-Operating_System
(	O
SVCs	O
)	O
rather	O
than	O
by	O
direct	O
use	O
of	O
SVCs	O
.	O
</s>
<s>
User	O
programs	O
may	O
never	O
refer	O
directly	O
to	O
any	O
system	O
control	O
block	O
(	O
neither	O
for	O
reference	O
nor	O
change	O
)	O
,	O
because	O
the	O
virtual	B-Architecture
memory	I-Architecture
segment(s )	O
that	O
contain	O
system	O
control	O
blocks	O
(	O
the	O
system	O
segments	O
)	O
are	O
removed	O
from	O
a	O
job	O
's	O
virtual	O
address	O
space	O
when	O
a	O
user	O
mode	O
program	O
is	O
running	O
.	O
</s>
<s>
The	O
subroutine	O
interfaces	O
available	O
to	O
user	O
programs	O
are	O
also	O
used	O
by	O
most	O
other	O
parts	O
of	O
the	O
system	O
(	O
system	O
mode	O
programs	O
,	O
CLSs	O
,	O
...	O
)	O
even	O
through	O
components	O
running	O
in	O
system	O
mode	O
do	O
have	O
access	O
to	O
the	O
"	O
system	O
"	O
virtual	B-Architecture
memory	I-Architecture
segment(s )	O
.	O
</s>
<s>
The	O
supervisor	B-Operating_System
,	O
most	O
job	O
programs	O
,	O
large	O
parts	O
of	O
MTS	O
including	O
many	O
DSRs	O
and	O
CLSs	O
are	O
written	O
in	O
360/370	O
assembler	O
language	O
.	O
</s>
<s>
A	O
few	O
job	O
programs	O
and	O
portions	O
of	O
MTS	O
including	O
some	O
DSRs	O
and	O
CLSs	O
are	O
written	O
in	O
higher	O
level	O
languages	O
such	O
as	O
Plus	B-Language
or	O
GOM	B-Language
.	O
</s>
<s>
Most	O
components	O
of	O
the	O
system	O
,	O
including	O
user	O
programs	O
,	O
CLSs	O
,	O
and	O
subroutines	O
loaded	O
in	O
shared	O
virtual	B-Architecture
memory	I-Architecture
,	O
can	O
be	O
debugged	O
and	O
new	O
versions	O
of	O
many	O
can	O
be	O
installed	O
while	O
the	O
system	O
is	O
running	O
without	O
requiring	O
a	O
system	O
shutdown	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
substitute	O
a	O
private	O
copy	O
of	O
all	O
components	O
except	O
the	O
supervisor	B-Operating_System
and	O
parts	O
of	O
some	O
job	O
programs	O
.	O
</s>
<s>
Components	O
that	O
cannot	O
be	O
debugged	O
in	O
this	O
way	O
can	O
be	O
debugged	O
by	O
running	O
in	O
an	O
MTS	O
virtual	B-Architecture
machine	I-Architecture
(	O
a	O
user	O
program	O
)	O
.	O
</s>
<s>
University	O
of	O
Michigan	O
Multi-Programming	O
Supervisor	B-Operating_System
(	O
UMMPS	O
)	O
is	O
the	O
name	O
of	O
the	O
MTS	O
supervisor	B-Operating_System
.	O
</s>
<s>
UMMPS	O
is	O
the	O
only	O
portion	O
of	O
the	O
system	O
that	O
runs	O
in	O
S/360	B-Application
supervisor	B-Operating_System
state	O
.	O
</s>
<s>
It	O
runs	O
with	O
virtual	B-Architecture
memory	I-Architecture
(	O
relocation	O
)	O
turned	O
off	O
and	O
with	O
hardware	B-Application
interrupts	I-Application
disabled	O
.	O
</s>
<s>
UMMPS	O
is	O
what	O
today	O
would	O
be	O
called	O
a	O
microkernel	B-Operating_System
,	O
although	O
UMMPS	O
was	O
developed	O
long	O
before	O
that	O
term	O
was	O
in	O
common	O
use	O
.	O
</s>
<s>
To	O
jobs	O
UMMPS	O
appears	O
to	O
be	O
an	O
extension	O
of	O
the	O
S/360	B-Application
or	O
S/370	B-Device
hardware	O
and	O
is	O
responsible	O
for	O
:	O
</s>
<s>
allocating	O
all	O
hardware	O
resources	O
(	O
processors	B-General_Concept
,	O
real	O
memory	O
,	O
input/output	O
devices	O
)	O
,	O
</s>
<s>
processing	O
all	O
hardware	B-Application
interrupts	I-Application
including	O
page-faults	O
and	O
program	O
interrupts	B-Application
due	O
to	O
errors	O
in	O
job	O
programs	O
,	O
</s>
<s>
implementing	O
virtual	B-Architecture
memory	I-Architecture
including	O
:	O
</s>
<s>
the	O
allocation	O
of	O
VM	B-Application
addresses	O
,	O
</s>
<s>
determining	O
when	O
and	O
which	O
pages	O
should	O
be	O
moved	O
between	O
real	O
memory	O
and	O
secondary	O
storage	O
to	O
implement	O
demand	B-General_Concept
paging	I-General_Concept
,	O
</s>
<s>
providing	O
services	O
to	O
job	O
programs	O
that	O
issue	O
Supervisor	B-Operating_System
Call	I-Operating_System
(	O
SVC	O
)	O
and	O
Monitor	O
call	O
(	O
MC	O
)	O
instructions	O
,	O
including	O
:	O
</s>
<s>
scheduling	O
timer	O
interrupts	B-Application
,	O
</s>
<s>
allowing	O
jobs	O
to	O
enter	O
and	O
leave	O
user	O
and	O
system	O
mode	O
,	O
where	O
user	O
mode	O
programs	O
do	O
not	O
have	O
access	O
to	O
some	O
virtual	B-Architecture
memory	I-Architecture
segments	O
and	O
the	O
full	O
range	O
of	O
SVCs	O
,	O
</s>
<s>
providing	O
shadow	O
segment	O
and	O
page	O
tables	O
and	O
other	O
services	O
that	O
allow	O
job	O
programs	O
to	O
provide	O
virtual	B-Architecture
machine	I-Architecture
services	O
,	O
</s>
<s>
simulating	O
a	O
few	O
machine	O
instructions	O
that	O
are	O
present	O
on	O
some	O
,	O
but	O
not	O
all	O
,	O
models	O
of	O
the	O
S/360	B-Application
or	O
S/370	B-Device
computers	O
,	O
</s>
<s>
simulating	O
the	O
Branch	O
on	O
Program	O
Interrupt	B-Application
(	O
BPI	O
)	O
pseudo	O
instructions	O
,	O
</s>
<s>
writing	O
job	O
dumps	O
(	O
making	O
a	O
snapshot	O
of	O
the	O
current	O
execution	O
state	O
of	O
a	O
job	O
by	O
writing	O
out	O
all	O
real	O
memory	O
,	O
all	O
the	O
job	O
's	O
virtual	B-Architecture
memory	I-Architecture
,	O
general	O
registers	O
,	O
and	O
program	O
status	O
word	O
to	O
magnetic	O
tape	O
)	O
,	O
</s>
<s>
After	O
initialization	O
UMMPS	O
is	O
entirely	O
interrupt	B-Application
driven	O
.	O
</s>
<s>
The	O
interrupts	B-Application
may	O
be	O
due	O
to	O
supervisor	B-Operating_System
(	O
SVC	O
)	O
or	O
monitor	O
(	O
MC	O
)	O
call	O
instructions	O
issued	O
by	O
job	O
programs	O
to	O
request	O
services	O
,	O
page	O
fault	O
interrupts	B-Application
for	O
virtual	B-Architecture
memory	I-Architecture
pages	O
that	O
are	O
not	O
in	O
real	O
memory	O
when	O
referenced	O
by	O
a	O
job	O
program	O
,	O
program	O
interrupts	B-Application
caused	O
by	O
abnormal	O
conditions	O
in	O
job	O
programs	O
,	O
timer	O
interrupts	B-Application
on	O
behalf	O
of	O
job	O
programs	O
or	O
used	O
internally	O
within	O
the	O
supervisor	B-Operating_System
,	O
interrupts	B-Application
from	O
the	O
input/output	O
subsystem	O
,	O
machine	O
check	O
interrupts	B-Application
,	O
external	O
(	O
operator	O
initiated	O
)	O
interrupts	B-Application
,	O
and	O
interrupts	B-Application
from	O
other	O
processors	B-General_Concept
in	O
a	O
multiprocessor	O
configuration	O
.	O
</s>
<s>
A	O
program	O
interrupt	B-Application
in	O
supervisor	B-Operating_System
state	O
is	O
a	O
system	O
failure	O
that	O
results	O
in	O
a	O
supervisor	B-Operating_System
dump	O
(	O
a	O
Super	O
Dump	O
,	O
where	O
the	O
machine	O
state	O
and	O
the	O
contents	O
of	O
all	O
real	O
memory	O
is	O
written	O
to	O
magnetic	O
tape	O
)	O
followed	O
by	O
a	O
system	O
restart	O
(	O
re-IPL	O
)	O
.	O
</s>
<s>
The	O
Branch	O
on	O
Program	O
Interrupt	B-Application
(	O
BPI	O
)	O
pseudo	O
instruction	O
provides	O
a	O
simple	O
way	O
for	O
a	O
sequence	O
of	O
code	O
to	O
retain	O
control	O
following	O
a	O
program	O
interrupt	B-Application
.	O
</s>
<s>
This	O
can	O
be	O
useful	O
to	O
test	O
for	O
valid	O
addresses	O
in	O
a	O
parameter	O
list	O
,	O
to	O
catch	O
overflow	O
,	O
underflow	O
,	O
and	O
other	O
exceptions	O
during	O
calculations	O
,	O
or	O
really	O
any	O
situation	O
where	O
a	O
program	O
interrupt	B-Application
is	O
possible	O
.	O
</s>
<s>
BPIs	O
can	O
be	O
used	O
at	O
very	O
low	O
cost	O
for	O
the	O
usually	O
more	O
common	O
case	O
where	O
there	O
is	O
no	O
program	O
interrupt	B-Application
.	O
</s>
<s>
UMMPS	O
implements	O
the	O
Branch	O
on	O
Program	O
Interrupt	B-Application
(	O
BPI	O
)	O
pseudo	O
instruction	O
using	O
a	O
special	O
type	O
of	O
NOP	O
instruction	O
.	O
</s>
<s>
The	O
BPI	O
instruction	O
is	O
available	O
for	O
use	O
in	O
problem-state	O
as	O
well	O
as	O
supervisor-state	O
(	O
that	O
is	O
,	O
within	O
UMMPS	O
itself	O
)	O
.	O
</s>
<s>
If	O
there	O
is	O
a	O
match	O
,	O
the	O
condition	O
code	O
is	O
set	O
to	O
reflect	O
the	O
interrupt	B-Application
that	O
occurred	O
and	O
the	O
branch	O
is	O
taken	O
.	O
</s>
<s>
If	O
there	O
is	O
no	O
BPI	O
transfer	O
made	O
(	O
either	O
because	O
there	O
was	O
no	O
BPI	O
instruction	O
or	O
because	O
the	O
program	O
interrupt	B-Application
type	O
did	O
not	O
match	O
the	O
mask	O
of	O
any	O
BPIs	O
that	O
were	O
present	O
)	O
,	O
the	O
normal	O
processing	O
of	O
the	O
program	O
interrupt	B-Application
occurs	O
.	O
</s>
<s>
When	O
the	O
BPI	O
instruction	O
is	O
executed	O
normally	O
(	O
when	O
there	O
is	O
no	O
program	O
interrupt	B-Application
on	O
the	O
previous	O
instruction	O
)	O
,	O
it	O
is	O
a	O
NOP	O
or	O
"	O
branch	O
never	O
"	O
instruction	O
.	O
</s>
<s>
BPI	O
interrupt-type	O
categories	O
:	O
</s>
<s>
All	O
job	O
programs	O
run	O
in	O
S/360	B-Application
problem	O
state	O
,	O
may	O
run	O
with	O
virtual	O
addressing	O
enabled	O
or	O
disabled	O
,	O
and	O
may	O
or	O
may	O
not	O
be	O
reentrant	O
(	O
more	O
than	O
one	O
instance	O
of	O
the	O
job	O
program	O
may	O
or	O
may	O
not	O
be	O
allowed	O
to	O
execute	O
)	O
.	O
</s>
<s>
With	O
multiprocessor	O
configurations	O
a	O
single	O
job	O
will	O
only	O
execute	O
on	O
a	O
single	O
processor	O
at	O
a	O
time	O
,	O
but	O
the	O
supervisor	B-Operating_System
may	O
assign	O
a	O
job	O
to	O
different	O
processors	B-General_Concept
at	O
different	O
times	O
.	O
</s>
<s>
Other	O
job	O
programs	O
assist	O
the	O
supervisor	B-Operating_System
(	O
the	O
Paging	O
Device	O
Processor	O
or	O
PDP	O
,	O
the	O
OPERATOR	O
console	O
job	O
,	O
the	O
Disk	O
Manager	O
or	O
DMGR	O
,	O
...	O
)	O
,	O
provide	O
common	O
or	O
shared	O
services	O
(	O
spooled	B-Device
local	O
and	O
remote	O
batch	O
services	O
via	O
HASP	B-Application
and	O
the	O
HASPlings	O
or	O
later	O
the	O
Resource	O
Manager	O
or	O
RM	O
which	O
was	O
developed	O
at	O
the	O
University	O
of	O
British	O
Columbia	O
to	O
replace	O
HASP	B-Application
)	O
,	O
or	O
allow	O
the	O
system	O
operators	O
to	O
display	O
status	O
and	O
otherwise	O
control	O
the	O
system	O
(	O
JOBS	O
,	O
UNITS	O
,	O
STOP	O
,	O
BLAST	O
,	O
GOOSE	O
,	O
STARTUP	O
,	O
SHUTDOWN	O
,	O
REW	O
,	O
WTM	O
,	O
...	O
)	O
.	O
</s>
<s>
The	O
very	O
first	O
job	O
,	O
INIT	O
,	O
is	O
started	O
immediately	O
after	O
IPL	O
and	O
supervisor	B-Operating_System
initialization	O
.	O
</s>
<s>
UMMPS	O
never	O
used	O
the	O
32-bit	O
virtual	B-Architecture
memory	I-Architecture
addresses	O
that	O
were	O
available	O
on	O
the	O
IBM	B-Device
S/360	I-Device
-67	I-Device
.	O
</s>
<s>
In	O
August	O
1982	O
the	O
University	O
of	O
Alberta	O
changed	O
UMMPS	O
to	O
operate	O
in	O
31-bit	O
addressing	O
mode	O
to	O
allow	O
more	O
than	O
16	O
MB	O
of	O
real	O
memory	O
to	O
be	O
used	O
,	O
although	O
real	O
memory	O
above	O
16	O
MB	O
was	O
only	O
used	O
for	O
to	O
hold	O
virtual	B-Architecture
memory	I-Architecture
pages	O
.	O
</s>
<s>
In	O
1985	O
Rensselaer	O
Polytechnic	O
Institute	O
(	O
RPI	O
)	O
made	O
changes	O
to	O
UMMPS	O
to	O
support	O
S/370	B-Device
-XA	I-Device
which	O
among	O
other	O
things	O
allowed	O
either	O
24	O
or	O
31-bit	O
addressing	O
for	O
job	O
programs	O
and	O
for	O
user	O
programs	O
running	O
under	O
MTS	O
.	O
</s>
<s>
MTS	O
has	O
a	O
strong	O
protection	O
model	O
that	O
uses	O
the	O
virtual	B-Architecture
memory	I-Architecture
hardware	O
and	O
the	O
S/360	B-Application
and	O
S/370	B-Device
hardware	O
's	O
supervisor	B-Operating_System
and	O
problem	O
states	O
and	O
via	O
software	O
divides	O
problem	O
state	O
execution	O
into	O
system	O
(	O
privileged	O
or	O
unprotected	O
)	O
and	O
user	O
(	O
protected	O
or	O
unprivileged	O
)	O
modes	O
.	O
</s>
<s>
Relatively	O
little	O
code	O
runs	O
in	O
supervisor	B-Operating_System
state	O
.	O
</s>
<s>
For	O
example	O
,	O
Device	O
Support	O
Routines	O
(	O
DSRs	O
,	O
aka	O
device	O
drivers	O
)	O
are	O
not	O
part	O
of	O
the	O
supervisor	B-Operating_System
and	O
run	O
in	O
system	O
mode	O
in	O
problem	O
state	O
rather	O
than	O
in	O
supervisor	B-Operating_System
state	O
.	O
</s>
<s>
Virtual	B-Architecture
memory	I-Architecture
(	O
VM	B-Application
)	O
and	O
demand	B-General_Concept
paging	I-General_Concept
support	O
were	O
added	O
to	O
UMMPS	O
in	O
November	O
1967	O
,	O
making	O
MTS	O
the	O
first	O
operating	B-General_Concept
system	I-General_Concept
to	O
use	O
the	O
Dynamic	O
Address	O
Translation	O
(	O
DAT	O
)	O
features	O
that	O
were	O
added	O
to	O
the	O
IBM	B-Device
S/360	I-Device
-67	I-Device
.	O
</s>
<s>
UMMPS	O
uses	O
4096-byte	O
virtual	B-Architecture
memory	I-Architecture
pages	O
and	O
256-page	O
virtual	B-Architecture
memory	I-Architecture
segments	O
.	O
</s>
<s>
UMMPS	O
could	O
be	O
conditionally	O
assembled	O
to	O
use	O
the	O
small	O
(	O
64	O
page	O
)	O
segments	O
that	O
were	O
available	O
on	O
S/370	B-Device
hardware	O
,	O
but	O
job	O
programs	O
were	O
always	O
presented	O
with	O
what	O
appeared	O
to	O
be	O
large	O
(	O
256	O
page	O
)	O
segments	O
.	O
</s>
<s>
High-speed	O
paging	O
devices	O
include	O
the	O
IBM	O
2301	O
Drum	O
,	O
IBM	B-Device
2305	I-Device
Fixed	I-Device
Head	I-Device
File	I-Device
,	O
and	O
various	O
third	O
party	O
"	O
solid-state	O
"	O
I/O	O
devices	O
such	O
as	O
the	O
STC	O
4305	O
and	O
Intel	O
3805	O
that	O
simulate	O
spinning	O
disks	O
or	O
more	O
often	O
provide	O
more	O
efficient	O
fixed	B-Device
block	I-Device
architecture	I-Device
(	O
FBA	O
)	O
access	O
to	O
external	O
RAM-based	O
storage	O
.	O
</s>
<s>
Virtual	B-Architecture
memory	I-Architecture
pages	O
migrate	O
between	O
real	O
memory	O
and	O
the	O
paging	O
devices	O
.	O
</s>
<s>
Later	O
in	O
its	O
life	O
the	O
system	O
was	O
changed	O
to	O
use	O
IBM	B-Device
S/370	I-Device
-XA	I-Device
Extended	O
Storage	O
as	O
part	O
of	O
the	O
second	O
level	O
of	O
the	O
storage	O
hierarchy	O
and	O
to	O
use	O
the	O
same	O
disks	O
for	O
the	O
file	O
system	O
and	O
for	O
paging	O
.	O
</s>
<s>
Virtual	B-Architecture
memory	I-Architecture
is	O
managed	O
by	O
UMMPS	O
with	O
assistance	O
from	O
the	O
Paging	O
Device	O
Processor	O
(	O
PDP	O
)	O
job	O
program	O
.	O
</s>
<s>
UMMPS	O
responds	O
to	O
requests	O
to	O
allocate	O
and	O
free	O
VM	B-Application
from	O
job	O
programs	O
,	O
allocates	O
VM	B-Application
addresses	O
,	O
allocates	O
real	O
memory	O
,	O
manages	O
segment	O
and	O
page	O
tables	O
,	O
sets	O
storage	O
keys	O
,	O
manages	O
reference	O
and	O
change	O
bits	O
,	O
determines	O
which	O
virtual	B-Architecture
memory	I-Architecture
pages	O
should	O
be	O
paged	O
in	O
or	O
out	O
,	O
and	O
communicates	O
with	O
the	O
PDP	O
.	O
</s>
<s>
New	O
virtual	B-Architecture
memory	I-Architecture
pages	O
are	O
initialized	O
to	O
a	O
"	O
core	O
constant	O
"	O
value	O
of	O
x'81'	O
on	O
first	O
reference	O
.	O
</s>
<s>
To	O
reduce	O
the	O
likelihood	O
of	O
thrashing	B-General_Concept
UMMPS	O
uses	O
a	O
"	O
big	O
job	O
mechanism	O
"	O
that	O
identifies	O
jobs	O
with	O
more	O
real	O
pages	O
than	O
a	O
threshold	O
,	O
limits	O
the	O
number	O
of	O
these	O
"	O
big	O
"	O
jobs	O
that	O
are	O
eligible	O
to	O
execute	O
at	O
a	O
given	O
time	O
,	O
and	O
gives	O
the	O
big	O
jobs	O
an	O
extended	O
time	O
slice	O
when	O
they	O
do	O
execute	O
.	O
</s>
<s>
The	O
number	O
of	O
pages	O
that	O
a	O
job	O
can	O
have	O
before	O
it	O
is	O
considered	O
big	O
(	O
the	O
big	O
job	O
threshold	O
or	O
BJT	O
)	O
and	O
the	O
number	O
of	O
big	O
jobs	O
(	O
NBJ	O
)	O
that	O
are	O
eligible	O
for	O
execution	O
are	O
external	O
parameters	O
that	O
are	O
reevaluated	O
and	O
set	O
outside	O
of	O
the	O
supervisor	B-Operating_System
every	O
20	O
seconds	O
based	O
on	O
the	O
overall	O
system	O
load	O
.	O
</s>
<s>
Virtual	B-Architecture
memory	I-Architecture
is	O
divided	O
into	O
regions	O
as	O
follows	O
:	O
</s>
<s>
Different	O
numbers	O
of	O
segments	O
were	O
assigned	O
to	O
the	O
various	O
regions	O
over	O
time	O
and	O
with	O
the	O
advent	O
of	O
31-bit	O
addressing	O
and	O
the	O
ability	O
to	O
use	O
VM	B-Application
segments	O
larger	O
than	O
16	O
,	O
the	O
regions	O
were	O
expanded	O
as	O
follows	O
:	O
</s>
<s>
Some	O
real	O
memory	O
is	O
not	O
addressable	O
using	O
virtual	B-Architecture
memory	I-Architecture
addresses	O
and	O
so	O
is	O
only	O
available	O
to	O
UMMPS	O
or	O
real	O
memory	O
job	O
programs	O
.	O
</s>
<s>
Read-only	O
virtual	B-Architecture
memory	I-Architecture
may	O
be	O
changed	O
by	O
privileged	O
programs	O
that	O
turn	O
memory	O
protection	O
off	O
(	O
usually	O
for	O
very	O
limited	O
periods	O
of	O
time	O
)	O
.	O
</s>
<s>
Named	O
address	O
spaces	O
(	O
NASs	O
)	O
allow	O
the	O
attachment	O
of	O
named	O
segments	O
of	O
virtual	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
They	O
are	O
shared	O
virtual	B-Architecture
memory	I-Architecture
spaces	O
that	O
may	O
be	O
attached	O
and	O
detached	O
from	O
a	O
given	O
job	O
's	O
virtual	O
address	O
space	O
and	O
the	O
same	O
addresses	O
may	O
have	O
different	O
contents	O
depending	O
on	O
which	O
named	O
address	O
spaces	O
are	O
attached	O
.	O
</s>
<s>
NAS	O
support	O
is	O
mostly	O
used	O
by	O
MTS	O
to	O
attach	O
VM	B-Application
segments	O
preloaded	O
with	O
system	O
components	O
as	O
a	O
way	O
to	O
extend	O
shared	O
virtual	B-Architecture
memory	I-Architecture
without	O
using	O
VM	B-Application
address	O
space	O
below	O
the	O
magic	O
16	O
MB	O
line	O
and	O
thus	O
keeping	O
more	O
of	O
this	O
valuable	O
address	O
space	O
available	O
for	O
use	O
by	O
24-bit	O
user	O
programs	O
.	O
</s>
<s>
Individuals	O
can	O
have	O
multiple	O
sign	O
on	O
IDs	O
for	O
use	O
in	O
different	O
courses	O
,	O
different	O
research	O
projects	O
,	O
or	O
with	O
different	O
funding	O
sources	O
(	O
university	O
,	O
government	O
,	O
non-profit	O
,	O
industry	O
,	O
...	O
)	O
.	O
</s>
<s>
Command	B-Application
lines	I-Application
that	O
end	O
with	O
a	O
continuation	O
character	O
(	O
by	O
default	O
the	O
minus-sign	O
)	O
are	O
continued	O
on	O
the	O
next	O
line	O
.	O
</s>
<s>
Command	B-Application
lines	I-Application
may	O
be	O
up	O
to	O
255	O
characters	O
long	O
.	O
</s>
<s>
The	O
command	O
verb	O
(	O
SIGNON	O
,	O
RUN	O
,	O
EDIT	O
,	O
...	O
)	O
is	O
the	O
first	O
keyword	O
on	O
the	O
command	B-Application
line	I-Application
.	O
</s>
<s>
Commands	O
may	O
start	O
with	O
an	O
optional	O
dollar-sign	O
( $SIGNON	O
,	O
$RUN	O
,	O
$EDIT	O
,	O
...	O
)	O
.	O
</s>
<s>
All	O
commands	O
and	O
most	O
command	O
options	O
allow	O
initial	O
sub-string	O
abbreviations	O
(	O
C	O
for	O
COPY	O
,	O
R	O
for	O
RUN	O
,	O
DEB	O
for	O
DEBUG	O
,	O
...	O
)	O
.	O
</s>
<s>
MTS	O
has	O
"	O
one-shot	O
"	O
commands	O
(	O
CREATE	O
,	O
FILESTATUS	O
,	O
SIGNOFF	O
,	O
...	O
)	O
and	O
commands	O
that	O
have	O
sub-command	O
modes	O
(	O
EDIT	O
,	O
CALC	O
,	O
SYSTEMSTATUS	O
,	O
...	O
)	O
.	O
</s>
<s>
Most	O
commands	O
with	O
sub-command	O
modes	O
can	O
also	O
be	O
invoked	O
as	O
one-shot	O
commands	O
by	O
giving	O
one	O
or	O
more	O
sub-commands	O
on	O
the	O
command	B-Application
line	I-Application
.	O
</s>
<s>
SET	O
option	O
...	O
</s>
<s>
START	O
[	O
[	O
AT	O
]	O
[	O
RF	O
={	O
hhhhhh	O
|	O
GRx}	O
]	O
location	O
]	O
[	O
I/Ounits	O
]	O
[	O
option	O
]	O
...	O
</s>
<s>
RESTART	O
[	O
[	O
AT	O
]	O
location	O
]	O
[	O
I/Ounits	O
]	O
[	O
option	O
]	O
...	O
</s>
<s>
ALTER	O
location	O
value	O
...	O
...	O
</s>
<s>
Other	O
MTS	O
commands	O
are	O
implemented	O
as	O
separate	O
modules	O
,	O
confusingly	O
also	O
named	O
command	O
language	O
subsystems	O
or	O
CLSs	O
,	O
that	O
may	O
be	O
executed	O
from	O
shared	O
virtual	B-Architecture
memory	I-Architecture
or	O
may	O
be	O
loaded	O
from	O
files	O
.	O
</s>
<s>
There	O
is	O
an	O
option	O
on	O
the	O
$UNLOAD	O
command	O
to	O
unload	O
a	O
CLS	O
(	O
free	O
the	O
virtual	B-Architecture
memory	I-Architecture
it	O
is	O
using	O
,	O
close	O
any	O
FDnames	O
and	O
release	O
any	O
devices	O
or	O
pseudo	O
devices	O
that	O
it	O
has	O
open	O
)	O
.	O
</s>
<s>
The	O
$RESTART	O
command	O
may	O
be	O
used	O
to	O
restart	O
execution	O
of	O
a	O
program	O
following	O
an	O
attention	O
interrupt	B-Application
that	O
was	O
not	O
handled	O
by	O
the	O
program	O
,	O
a	O
program	O
interrupt	B-Application
that	O
was	O
not	O
handled	O
by	O
the	O
program	O
(	O
although	O
restarting	O
after	O
a	O
program	O
interrupt	B-Application
usually	O
does	O
not	O
work	O
well	O
)	O
,	O
or	O
following	O
an	O
explicit	O
return	O
to	O
MTS	O
from	O
a	O
call	O
to	O
the	O
MTS	O
subroutine	O
.	O
</s>
<s>
MTS	O
loads	O
programs	O
using	O
a	O
dynamic	O
linking	O
loader	O
(	O
UMLOAD	O
)	O
that	O
reads	O
loader	O
records	O
(	O
ESD	O
,	O
TXT	O
,	O
CSI	O
,	O
RDL	O
,	O
LCS	O
,	O
END	O
,	O
...	O
)	O
from	O
the	O
file	O
or	O
device	O
specified	O
by	O
the	O
user	O
and	O
will	O
selectively	O
include	O
subroutines	O
from	O
libraries	O
supplied	O
by	O
the	O
user	O
,	O
from	O
system	O
subroutine	O
libraries	O
such	O
as	O
*	O
LIBRARY	O
,	O
and	O
from	O
system	O
subroutines	O
pre-loaded	O
in	O
shared	O
virtual	B-Architecture
memory	I-Architecture
.	O
</s>
<s>
MTS	O
uses	O
standard	O
OS/360	O
loader	O
records	O
which	O
makes	O
it	O
fairly	O
easy	O
for	O
MTS	O
to	O
use	O
compilers	O
developed	O
for	O
use	O
under	O
other	O
IBM	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
User	O
mode	O
programs	O
do	O
not	O
have	O
access	O
to	O
the	O
system	O
virtual	B-Architecture
memory	I-Architecture
segment	O
and	O
therefore	O
have	O
no	O
access	O
to	O
system	O
control	O
blocks	O
,	O
may	O
not	O
call	O
privileged	O
system	O
subroutines	O
,	O
and	O
may	O
not	O
issue	O
privileged	O
supervisor	B-Operating_System
calls	I-Operating_System
(	O
SVCs	O
)	O
.	O
</s>
<s>
All	O
input/output	O
requests	O
,	O
whether	O
by	O
the	O
MTS	O
job	O
program	O
itself	O
or	O
by	O
a	O
program	O
running	O
under	O
MTS	O
,	O
is	O
done	O
using	O
a	O
common	O
set	O
of	O
subroutine	O
calls	O
(	O
GETFD	O
,	O
FREEFD	O
,	O
READ	O
,	O
WRITE	O
,	O
CONTROL	O
,	O
GDINFO	O
,	O
ATTNTRP	O
,	O
...	O
)	O
.	O
</s>
<s>
Conversion	O
to	O
and	O
from	O
ASCII/EBCDIC	O
and	O
end-of-line	O
processing	O
is	O
usually	O
done	O
by	O
a	O
front	O
end	O
processor	O
or	O
Device	O
Support	O
Routine	O
(	O
DSR	O
)	O
and	O
so	O
is	O
not	O
a	O
concern	O
of	O
most	O
programs	O
.	O
</s>
<s>
*	O
SOURCE*	O
standard	O
input	O
(	O
normally	O
either	O
a	O
terminal	O
or	O
for	O
batch	O
jobs	O
,	O
the	O
input	O
queue	B-Device
)	O
;	O
</s>
<s>
*	O
BATCH*	O
spooled	B-Device
input	O
to	O
a	O
new	O
batch	O
job	O
;	O
</s>
<s>
*	O
PRINT*	O
spooled	B-Device
output	O
to	O
a	O
printer	O
,	O
same	O
as	O
*	O
MSINK*	O
for	O
batch	O
jobs	O
;	O
</s>
<s>
The	O
$CREATE	O
command	O
can	O
be	O
used	O
to	O
create	O
pseudo	O
device	O
names	O
for	O
use	O
with	O
BITNET	B-General_Concept
import	O
and	O
export	O
,	O
for	O
spooled	B-Device
print	O
jobs	O
,	O
and	O
for	O
dummy	O
devices	O
.	O
</s>
<s>
Some	O
commonly	O
used	O
I/O	O
modifiers	O
are	O
:	O
@S	O
(	O
sequential	O
)	O
,	O
@I	O
(	O
indexed	O
)	O
,	O
@FWD	O
(	O
forward	O
)	O
,	O
@BKWD	O
(	O
backward	O
)	O
,	O
@EBCD	O
(	O
EBCDIC	B-Language
)	O
,	O
@BIN	O
(	O
binary	O
)	O
,	O
@UC	O
(	O
uppercase	O
)	O
,	O
@CC	O
(	O
logical	O
carriage	O
control	O
)	O
,	O
@MCC	O
(	O
machine	O
carriage	O
control	O
)	O
,	O
@NOCC	O
(	O
no	O
carriage	O
control	O
)	O
,	O
@TRIM	O
(	O
trim	O
all	O
but	O
last	O
training	O
blank	O
)	O
.	O
</s>
<s>
Explicit	O
concatenation	O
allows	O
FDnames	O
to	O
be	O
connected	O
using	O
a	O
plus-sign	O
,	O
as	O
NAMEA+NAMEB	O
.	O
</s>
<s>
Volumes	O
have	O
volume	O
labels	O
,	O
volume	O
numbers	O
,	O
and	O
volume	O
names	O
(	O
usually	O
MTS001	O
,	O
MTS002	O
,	O
...	O
,	O
MTSnnn	O
)	O
.	O
</s>
<s>
Disk	O
volumes	O
are	O
stored	O
on	O
traditional	O
cylinder-track-record	B-Application
and	O
fixed	B-Device
block	I-Device
architecture	I-Device
(	O
FBA	O
)	O
disk	O
drives	O
or	O
at	O
one	O
time	O
on	O
the	O
IBM	B-Device
2321	I-Device
Data	I-Device
Cell	I-Device
.	O
</s>
<s>
MTS	O
does	O
n't	O
implement	O
directories	B-Application
,	O
but	O
there	O
is	O
a	O
de	O
facto	O
two-tier	O
grouping	O
of	O
files	O
owing	O
to	O
the	O
inclusion	O
in	O
a	O
file	O
's	O
name	O
of	O
its	O
owner	O
's	O
four-character	O
MTS	O
user	O
ID	O
.	O
</s>
<s>
Allowed	O
line	O
numbers	O
are	O
±	O
2147483.647	O
—	O
essentially	O
a	O
signed	O
integer	O
value	O
divided	O
by	O
1000	O
,	O
but	O
command	B-Application
line	I-Application
references	O
were	O
limited	O
to	O
±	O
99999.999	O
.	O
</s>
<s>
Because	O
line	O
files	O
did	O
not	O
work	O
well	O
with	O
the	O
Data	B-Device
Cell	I-Device
,	O
SEQWL	O
files	O
were	O
implemented	O
as	O
a	O
way	O
to	O
allow	O
the	O
Data	B-Device
Cell	I-Device
to	O
be	O
used	O
for	O
longer	O
term	O
less	O
expensive	O
storage	O
of	O
files	O
while	O
still	O
preserving	O
line	O
numbers	O
.	O
</s>
<s>
When	O
an	O
attempt	O
to	O
lock	O
a	O
file	O
cannot	O
be	O
satisfied	O
,	O
the	O
calling	O
task	O
will	O
wait	O
either	O
indefinitely	O
or	O
for	O
a	O
specific	O
period	O
for	O
another	O
task	O
to	O
unlock	O
the	O
file	O
,	O
or	O
until	O
an	O
attention	O
interrupt	B-Application
is	O
received	O
.	O
</s>
<s>
The	O
file	O
locking	O
software	O
detects	O
deadlocks	O
between	O
tasks	O
using	O
Warshall	B-Algorithm
's	I-Algorithm
algorithm	I-Algorithm
and	O
returns	O
an	O
error	O
indication	O
without	O
locking	O
the	O
file	O
and	O
without	O
waiting	O
.	O
</s>
<s>
Terminals	B-General_Concept
are	O
attached	O
to	O
MTS	O
over	O
dial-in	O
modems	O
,	O
leased	O
or	O
dedicated	O
data	O
circuits	O
,	O
and	O
network	O
connections	O
.	O
</s>
<s>
</s>
<s>
Most	O
terminals	B-General_Concept
that	O
are	O
compatible	O
with	O
any	O
of	O
these	O
models	O
are	O
also	O
supported	O
.	O
</s>
<s>
1	O
,	O
August	O
1975	O
IBM	B-Device
1052	I-Device
consoles	O
,	O
IBM	O
3066	O
console	O
displays	O
,	O
and	O
IBM	B-Operating_System
3270	I-Operating_System
family	O
of	O
locally	O
attached	O
displays	O
(	O
IBM	O
3272	O
and	O
3274	O
control	O
units	O
,	O
but	O
not	O
remote	O
3270	B-Operating_System
displays	O
)	O
.	O
</s>
<s>
MTS	O
can	O
and	O
does	O
use	O
communication	O
controllers	O
such	O
as	O
the	O
IBM	O
2703	O
and	O
the	O
Memorex	O
1270	O
to	O
support	O
dial-in	O
terminals	B-General_Concept
and	O
remote	O
batch	O
stations	O
over	O
dial-in	O
and	O
dedicated	O
data	O
circuits	O
,	O
but	O
these	O
controllers	O
proved	O
to	O
be	O
fairly	O
inflexible	O
and	O
unsatisfactory	O
for	O
connecting	O
large	O
numbers	O
of	O
diverse	O
terminals	B-General_Concept
and	O
later	O
personal	B-Device
computers	I-Device
running	O
terminal	B-Application
emulation	I-Application
software	O
at	O
ever	O
higher	O
data	O
rates	O
.	O
</s>
<s>
Most	O
MTS	O
sites	O
choose	O
to	O
build	O
their	O
own	O
front-end	O
processors	B-General_Concept
or	O
to	O
use	O
a	O
front-end	O
processor	O
developed	O
by	O
one	O
of	O
the	O
other	O
MTS	O
sites	O
to	O
provide	O
terminal	O
support	O
.	O
</s>
<s>
These	O
front-end	O
processors	B-General_Concept
,	O
usually	O
DEC	B-Device
PDP-8	I-Device
,	O
PDP-11	B-Device
,	O
or	O
LSI-11	O
based	O
with	O
locally	O
developed	O
custom	O
hardware	O
and	O
software	O
,	O
would	O
act	O
as	O
IBM	O
control	O
units	O
attached	O
to	O
the	O
IBM	O
input/output	O
channels	O
on	O
one	O
side	O
and	O
to	O
modems	O
and	O
phone	O
lines	O
on	O
the	O
other	O
.	O
</s>
<s>
At	O
the	O
University	O
of	O
Michigan	O
the	O
front-end	O
processor	O
was	O
known	O
as	O
the	O
Data	O
Concentrator	O
(	O
DC	O
)	O
.The	O
Data	O
Concentrator	O
,	O
a	O
special-purpose	O
peripheral	O
device	O
for	O
the	O
attachment	O
of	O
interactive	O
terminals	B-General_Concept
to	O
the	O
System/360	B-Device
Model	I-Device
67	I-Device
,	O
overview	O
and	O
photos	O
from	O
Dave	O
Mills	O
,	O
the	O
project	O
leader	O
and	O
chief	O
designer	O
during	O
its	O
development	O
The	O
DC	O
was	O
developed	O
as	O
part	O
of	O
the	O
CONCOMP	O
project	O
by	O
Dave	O
Mills	O
and	O
others	O
and	O
was	O
the	O
first	O
non-IBM	O
device	O
developed	O
for	O
attachment	O
to	O
an	O
IBM	O
I/O	O
Channel.The	O
Data	O
Concentrator	O
,	O
David	O
L	O
.	O
Mills	O
,	O
CONCOMP	O
Project	O
,	O
University	O
of	O
Michigan	O
,	O
1968	O
Initially	O
a	O
PDP-8	B-Device
based	O
system	O
,	O
the	O
DC	O
was	O
upgraded	O
to	O
use	O
PDP-11	B-Device
hardware	O
and	O
a	O
Remote	O
Data	O
Concentrator	O
(	O
RDC	O
)	O
was	O
developed	O
that	O
used	O
LSI-11	O
hardware	O
that	O
connected	O
back	O
to	O
a	O
DC	O
over	O
a	O
synchronous	O
data	O
circuit	O
.	O
</s>
<s>
The	O
University	O
of	O
British	O
Columbia	O
(	O
UBC	O
)	O
developed	O
two	O
PDP-11	B-Device
based	O
systems	O
:	O
the	O
Host	O
Interface	O
Machine	O
(	O
HIM	O
)	O
and	O
the	O
Network	O
Interface	O
Machine	O
(	O
NIM	O
)	O
.	O
</s>
<s>
The	O
University	O
of	O
Alberta	O
used	O
a	O
PDP-11	B-Device
based	O
Front-end	O
processor	O
.	O
</s>
<s>
The	O
Merit	O
nodes	O
were	O
PDP-11	B-Device
based	O
and	O
used	O
custom	O
hardware	O
and	O
software	O
to	O
provide	O
host	O
to	O
host	O
interactive	O
connections	O
between	O
MTS	O
systems	O
and	O
between	O
MTS	O
and	O
the	O
CDC	O
SCOPE/HUSTLER	O
system	O
at	O
Michigan	O
State	O
University	O
(	O
MSU	O
)	O
.	O
</s>
<s>
Merit	O
renamed	O
its	O
Communication	O
Computers	O
to	O
be	O
Primary	O
Communication	O
Processors	B-General_Concept
(	O
PCPs	O
)	O
and	O
created	O
LSI-11	O
based	O
Secondary	O
Communication	O
Processors	B-General_Concept
(	O
SCPs	O
)	O
.	O
</s>
<s>
PCPs	O
and	O
SCPs	O
would	O
eventually	O
include	O
Ethernet	O
interfaces	O
and	O
support	O
local	B-General_Concept
area	I-General_Concept
network	I-General_Concept
(	O
LAN	B-General_Concept
)	O
attachments	O
.	O
</s>
<s>
PCPs	O
would	O
also	O
serve	O
as	O
gateways	O
to	O
commercial	O
networks	O
such	O
as	O
GTE	O
's	O
Telenet	O
(	O
later	O
SprintNet	O
)	O
,	O
Tymnet	B-Application
,	O
and	O
ADP	O
's	O
Autonet	O
,	O
providing	O
national	O
and	O
international	O
network	O
access	O
to	O
MTS	O
.	O
</s>
<s>
Later	O
still	O
the	O
PCPs	O
provided	O
gateway	O
services	O
to	O
the	O
TCP/IP	B-Protocol
networks	I-Protocol
that	O
became	O
today	O
's	O
Internet	O
.	O
</s>
<s>
UMMPS	O
provides	O
facilities	O
that	O
allow	O
the	O
creation	O
of	O
virtual	O
environments	O
,	O
either	O
virtual	B-Architecture
machines	I-Architecture
or	O
virtual	B-Architecture
operating	I-Architecture
systems	I-Architecture
.	O
</s>
<s>
The	O
initial	O
work	O
on	O
the	O
first	O
MTS	O
virtual	B-Architecture
machine	I-Architecture
was	O
done	O
at	O
the	O
University	O
of	O
Michigan	O
to	O
simulate	O
the	O
IBM	B-Device
S/360	I-Device
-67	I-Device
and	O
allow	O
debugging	O
of	O
UMMPS	O
and	O
MTS	O
.	O
</s>
<s>
Later	O
the	O
University	O
of	O
British	O
Columbia	O
did	O
the	O
initial	O
work	O
to	O
create	O
a	O
S/370	B-Device
MTS	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
In	O
theory	O
these	O
virtual	B-Architecture
machines	I-Architecture
could	O
be	O
used	O
to	O
run	O
any	O
S/360	B-Application
or	O
S/370	B-Device
system	O
,	O
but	O
in	O
practice	O
the	O
virtual	B-Architecture
machines	I-Architecture
were	O
only	O
used	O
to	O
debug	O
MTS	O
and	O
so	O
there	O
may	O
be	O
subtle	O
features	O
that	O
are	O
not	O
used	O
by	O
MTS	O
that	O
are	O
not	O
completely	O
or	O
correctly	O
implemented	O
.	O
</s>
<s>
The	O
MTS	O
virtual	B-Architecture
machine	I-Architecture
was	O
never	O
updated	O
to	O
support	O
the	O
S/370	B-Device
-XA	I-Device
architecture	O
(	O
instead	O
other	O
tools	O
such	O
as	O
SWAT	O
and	O
PEEK	O
were	O
used	O
to	O
debug	O
MTS	O
and	O
IBM	O
's	O
VM/XA	B-Application
or	O
VM/ESA	B-Application
were	O
used	O
to	O
debug	O
UMMPS	O
)	O
.	O
</s>
<s>
In	O
the	O
early	O
1970s	O
work	O
was	O
done	O
at	O
Wayne	O
State	O
University	O
to	O
run	O
a	O
version	O
of	O
OS/MVT	O
in	O
a	O
modified	O
virtual	B-Architecture
machine	I-Architecture
(	O
VOS	O
)	O
under	O
MTS	O
as	O
a	O
production	O
service	O
.	O
</s>
<s>
"	O
An	O
efficient	O
virtual	B-Architecture
machine	I-Architecture
implementation	O
"	O
,	O
R	O
.	O
J	O
.	O
Srodawa	O
and	O
L	O
.	O
A	O
.	O
Bates	O
,	O
Wayne	O
State	O
University	O
,	O
afips	O
,	O
pp	O
.	O
</s>
<s>
"	O
Student	O
"	O
virtual	B-Architecture
machines	I-Architecture
in	O
MTS	O
have	O
also	O
been	O
created	O
as	O
teaching	O
tools	O
.	O
</s>
<s>
Here	O
the	O
OS	O
running	O
in	O
the	O
virtual	B-Architecture
machine	I-Architecture
(	O
written	O
by	O
the	O
student	O
)	O
uses	O
simulated	O
devices	O
and	O
has	O
no	O
connection	O
to	O
the	O
"	O
real	O
"	O
outside	O
world	O
at	O
all	O
(	O
except	O
possibly	O
a	O
console	O
)	O
.	O
</s>
<s>
In	O
addition	O
to	O
virtual	B-Architecture
machines	I-Architecture
,	O
MTS	O
provides	O
two	O
programs	O
that	O
implement	O
virtual	B-Architecture
operating	I-Architecture
system	I-Architecture
environments.MTS	O
Volume	O
2	O
:	O
Public	O
File	O
Descriptions	O
,	O
University	O
of	O
Michigan	O
Computing	O
Center	O
,	O
Ann	O
Arbor	O
,	O
Michigan	O
*	O
FAKEOS	O
,	O
developed	O
at	O
the	O
University	O
of	O
Michigan	O
,	O
allows	O
programs	O
from	O
OS/360	O
to	O
run	O
as	O
user	O
programs	O
in	O
MTS	O
.	O
</s>
<s>
*	O
VSS	O
,	O
developed	O
at	O
the	O
University	O
of	O
British	O
Columbia	O
,	O
allows	O
programs	O
from	O
OS/VS1	B-Application
and	O
MVS/370	O
to	O
run	O
as	O
user	O
programs	O
in	O
MTS.MSC/NASTRAN	O
is	O
an	O
early	O
example	O
,	O
perhaps	O
too	O
early	O
,	O
of	O
the	O
use	O
of	O
*	O
VSS	O
,	O
see	O
MSC/NASTRAN	O
at	O
the	O
University	O
of	O
Michigan	O
,	O
William	O
J	O
.	O
Anderson	O
and	O
Robert	O
E	O
.	O
Sandstorm	O
,	O
1982	O
,	O
University	O
of	O
Michigan	O
College	O
of	O
Engineering	O
Neither	O
program	O
actually	O
runs	O
the	O
IBM	O
operating	B-General_Concept
system	I-General_Concept
,	O
instead	O
they	O
simulate	O
enough	O
of	O
the	O
operating	O
environment	O
to	O
allow	O
individual	O
programs	O
developed	O
for	O
those	O
operating	B-General_Concept
systems	I-General_Concept
to	O
run	O
.	O
</s>
<s>
CONFER	B-Protocol
and	O
*	O
MAIL	O
only	O
sent	O
and	O
received	O
mail	O
to	O
and	O
from	O
"	O
local	O
"	O
users	O
.	O
</s>
<s>
to	O
retrieve	O
incoming	O
and	O
outgoing	O
messages	O
using	O
a	O
database	O
model	O
(	O
incoming	O
,	O
outgoing	O
,	O
new	O
,	O
old/seen	O
,	O
to	O
recipients	O
,	O
from	O
recipients	O
,	O
message	O
number	O
,	O
date	O
sent	O
,	O
expiration	O
date	O
,	O
...	O
)	O
;	O
</s>
<s>
An	O
application	O
for	O
the	O
Apple	B-Device
Macintosh	I-Device
,	O
InfoX	O
(	O
aka	O
MacHost	O
)	O
,	O
was	O
developed	O
to	O
provide	O
a	O
modern	O
interface	O
to	O
the	O
MTS	O
Message	O
System	O
and	O
*	O
USERDIRECTORY	O
.	O
</s>
<s>
MIT	O
served	O
as	O
a	O
relay	O
hub	O
between	O
the	O
MAILNET	O
sites	O
and	O
as	O
a	O
gateway	O
to	O
CSNET	O
,	O
ARPANET	O
,	O
and	O
BITNET	B-General_Concept
.	O
</s>
<s>
MTS	O
at	O
the	O
University	O
of	O
Michigan	O
used	O
its	O
connections	O
to	O
the	O
Merit	O
Network	O
and	O
through	O
Merit	O
to	O
GTE	O
's	O
commercial	O
X.25	B-Protocol
network	O
,	O
Telenet	O
(	O
later	O
SprintNet	O
)	O
,	O
to	O
communicate	O
with	O
MIT	O
.	O
</s>
<s>
InfoX	O
(	O
pronounced	O
"	O
info-ex	O
"	O
,	O
originally	O
InfoDisk	O
)	O
is	O
a	O
program	O
for	O
the	O
Apple	B-Device
Macintosh	I-Device
developed	O
by	O
the	O
Information	O
Technology	O
Division	O
at	O
the	O
University	O
of	O
Michigan	O
.	O
</s>
<s>
It	O
provides	O
a	O
modern	O
user	O
interface	O
(	O
menus	O
,	O
icons	O
,	O
windows	O
,	O
and	O
buttons	O
)	O
that	O
can	O
be	O
used	O
to	O
check	O
MTS	O
electronic	O
mail	O
,	O
participate	O
in	O
CONFER	B-Protocol
II	I-Protocol
conferences	O
,	O
access	O
the	O
MTS	O
User	O
Directory	B-Application
,	O
and	O
create	O
,	O
edit	O
,	O
and	O
manipulate	O
files	O
.	O
</s>
<s>
InfoX	O
adds	O
Macintosh-style	O
word	O
processing	O
features	O
to	O
the	O
more	O
traditional	O
editing	O
functions	O
available	O
from	O
the	O
MTS	O
,	O
$Message	O
,	O
$Edit	O
,	O
and	O
CONFER	B-Protocol
command-line	B-Application
interfaces	I-Application
.	O
</s>
<s>
One	O
can	O
use	O
the	O
standard	O
Cut	O
,	O
Copy	O
,	O
and	O
Paste	O
commands	O
under	O
the	O
Macintosh	B-Device
Edit	O
menu	O
to	O
move	O
text	O
from	O
any	O
Macintosh	B-Device
file	O
.	O
</s>
<s>
Each	O
signon	O
ID	O
is	O
allocated	O
resource	O
limits	O
(	O
money	O
,	O
disk	O
space	O
,	O
connect	O
time	O
,	O
...	O
)	O
which	O
control	O
the	O
amount	O
and	O
types	O
of	O
work	O
that	O
can	O
be	O
done	O
by	O
the	O
ID	O
.	O
</s>
<s>
Memory	O
usage	O
—	O
charged	O
as	O
CPU-VM	O
integral	O
...	O
e.g.	O
</s>
<s>
Note	O
that	O
while	O
there	O
is	O
a	O
charge	O
for	O
virtual	B-Architecture
memory	I-Architecture
used	O
,	O
there	O
is	O
no	O
charge	O
for	O
real	O
memory	O
used	O
.	O
</s>
<s>
Different	O
rates	O
can	O
be	O
changed	O
for	O
different	O
classes	O
of	O
projects	O
(	O
internal	O
,	O
external	O
,	O
commercial	O
,	O
...	O
)	O
and	O
for	O
different	O
times	O
of	O
the	O
day	O
or	O
days	O
of	O
the	O
week	O
.	O
</s>
