<s>
SIMMON	B-Operating_System
(	O
SIMulation	O
MONitor	O
)	O
was	O
a	O
proprietary	B-Application
software	I-Application
testing	O
system	O
developed	O
in	O
the	O
late	O
1960s	O
in	O
the	O
IBM	O
Product	O
Test	O
Laboratory	O
,	O
then	O
at	O
Poughkeepsie	O
,	O
New	O
York	O
It	O
was	O
designed	O
for	O
the	O
then-new	O
line	O
of	O
System/360	B-Application
computers	O
as	O
a	O
vehicle	O
for	O
testing	O
the	O
software	O
that	O
IBM	O
was	O
developing	O
for	O
that	O
architecture	B-Architecture
.	O
</s>
<s>
SIMMON	B-Operating_System
was	O
first	O
described	O
at	O
the	O
IBM	O
SimSymp	O
1968	O
symposium	O
,	O
held	O
at	O
Rye	O
,	O
New	O
York	O
.	O
</s>
<s>
SIMMON	B-Operating_System
was	O
a	O
hypervisor	B-Operating_System
,	O
similar	O
to	O
the	O
IBM	B-Application
CP-40	I-Application
system	O
that	O
was	O
being	O
independently	O
developed	O
at	O
the	O
Cambridge	O
Scientific	O
Center	O
at	O
about	O
that	O
same	O
time	O
.	O
</s>
<s>
The	O
chief	O
difference	O
from	O
CP-40	B-Application
was	O
that	O
SIMMON	B-Operating_System
supported	O
a	O
single	O
virtual	B-Architecture
machine	I-Architecture
for	O
testing	O
of	O
a	O
single	O
guest	O
program	O
running	O
there	O
.	O
</s>
<s>
CP-40	B-Application
supported	O
many	O
virtual	B-Architecture
machines	I-Architecture
for	O
time-sharing	B-General_Concept
production	O
work	O
.	O
</s>
<s>
CP-40	B-Application
evolved	O
by	O
many	O
stages	O
into	O
the	O
present	O
VM/CMS	B-Application
operating	O
system	O
.	O
</s>
<s>
SIMMON	B-Operating_System
was	O
a	O
useful	O
test	O
vehicle	O
for	O
many	O
years	O
.	O
</s>
<s>
SIMMON	B-Operating_System
was	O
designed	O
to	O
dynamically	O
include	O
independently	O
developed	O
programs	O
(	O
test	O
tools	O
)	O
for	O
testing	O
the	O
target	O
guest	O
program	O
.	O
</s>
<s>
The	O
SIMMON	B-Operating_System
kernel	B-Operating_System
maintained	O
control	O
over	O
the	O
hardware	O
(	O
and	O
the	O
guest	O
)	O
and	O
coordinated	O
invocation	O
of	O
the	O
test	O
tools	O
.	O
</s>
<s>
As	O
an	O
Instruction	B-Application
Set	I-Application
Simulator	I-Application
,	O
SIMMON	B-Operating_System
was	O
unusual	O
in	O
that	O
it	O
simulated	O
the	O
same	O
architecture	B-Architecture
as	O
that	O
on	O
which	O
it	O
was	O
running	O
,	O
i.e.	O
</s>
<s>
While	O
an	O
order	O
of	O
magnitude	O
slower	O
than	O
Interrupt	B-Application
mode	O
(	O
below	O
)	O
,	O
it	O
allowed	O
close	O
attention	O
to	O
the	O
operation	O
of	O
the	O
guest	O
.	O
</s>
<s>
Interrupt	B-Application
mode	O
(	O
a/k/a	O
Bump	O
mode	O
)	O
constrained	O
the	O
guest	O
program	O
to	O
run	O
in	O
user	B-General_Concept
program	I-General_Concept
state	I-General_Concept
,	O
with	O
the	O
SIMMON	B-Operating_System
kernel	B-Operating_System
handling	O
all	O
hardware	O
interrupts	B-Application
and	O
simulating	O
all	O
privileged	O
instructions	O
the	O
guest	O
attempted	O
to	O
execute	O
.	O
</s>
<s>
These	O
were	O
some	O
test	O
tools	O
that	O
were	O
developed	O
for	O
use	O
with	O
SIMMON	B-Operating_System
.	O
</s>
<s>
This	O
test	O
tool	O
was	O
developed	O
to	O
test	O
the	O
device	B-General_Concept
support	I-General_Concept
error	O
recovery	O
in	O
IBM	O
's	O
PCP	O
(	O
Primary	O
Control	O
Program	O
)	O
operating	O
system	O
,	O
then	O
being	O
developed	O
.	O
</s>
<s>
It	O
used	O
a	O
novel	O
and	O
very	O
efficient	O
table-driven	O
finite-state	B-Architecture
machine	I-Architecture
(	O
FSM	O
)	O
to	O
inject	O
simulated	O
errors	O
and	O
verify	O
that	O
the	O
operating	O
system	O
followed	O
the	O
detailed	O
specifications	O
of	O
actions	O
to	O
be	O
taken	O
to	O
attempt	O
recovery	O
.	O
</s>
<s>
It	O
operated	O
by	O
allowing	O
the	O
program	O
under	O
test	O
to	O
run	O
in	O
Interrupt	B-Application
mode	O
,	O
but	O
also	O
used	O
the	O
system	O
timer	O
to	O
periodically	O
interrupt	B-Application
it	O
.	O
</s>
<s>
The	O
addresses	O
where	O
the	O
tested	O
program	O
was	O
interrupted	O
were	O
recorded	O
and	O
later	O
summarized	O
and	O
tabulated	O
in	O
the	O
form	O
of	O
a	O
map	O
,	O
showing	O
the	O
density	O
of	O
interrupts	B-Application
over	O
the	O
memory	O
addresses	O
.	O
</s>
<s>
The	O
report	O
took	O
the	O
form	O
of	O
a	O
listing	O
similar	O
to	O
a	O
storage	B-Error_Name
dump	I-Error_Name
,	O
with	O
program	O
entry	O
points	O
and	O
exit	O
points	O
identified	O
,	O
including	O
frequency	O
of	O
use	O
for	O
each	O
instruction	O
sequence	O
.	O
</s>
<s>
These	O
data	O
identified	O
the	O
Memory	B-General_Concept
Management	I-General_Concept
component	O
as	O
consuming	O
about	O
20%	O
of	O
CPU	O
resources	O
,	O
and	O
was	O
used	O
to	O
justify	O
a	O
task	O
force	O
to	O
try	O
to	O
improve	O
the	O
performance	O
.	O
</s>
<s>
While	O
not	O
a	O
specific	O
test	O
tool	O
,	O
the	O
distorted	O
timing	O
relationships	O
while	O
running	O
under	O
SIMMON	B-Operating_System
found	O
a	O
number	O
of	O
problems	O
,	O
particularly	O
in	O
the	O
input/output	B-General_Concept
sections	O
.	O
</s>
<s>
Unless	O
a	O
SIMMON	B-Operating_System
tool	O
was	O
put	O
in	O
place	O
to	O
normalize	O
and	O
delay	O
I/O	B-General_Concept
events	O
,	O
these	O
would	O
appear	O
to	O
the	O
guest	O
program	O
as	O
happening	O
unnaturally	O
quickly	O
.	O
</s>
<s>
Programs	O
under	O
test	O
--	O
so-called	O
guest	O
programs	O
--	O
had	O
to	O
be	O
capable	O
of	O
stand-alone	B-General_Concept
operation	O
on	O
the	O
bare	O
hardware	O
.	O
</s>
<s>
SIMMON	B-Operating_System
provided	O
services	O
for	O
the	O
test	O
tools	O
,	O
but	O
not	O
for	O
the	O
guest	O
.	O
</s>
<s>
These	O
were	O
some	O
of	O
the	O
programs	O
that	O
had	O
been	O
tested	O
using	O
SIMMON	B-Operating_System
:	O
</s>
<s>
OS/360	B-Application
(	O
PCP	O
.	O
</s>
