<s>
The	O
Monroe	O
Calculating	O
Machine	O
Mark	O
XI	O
(	O
or	O
Monrobot	B-Device
XI	I-Device
)	O
was	O
a	O
general-purpose	O
stored-program	O
electronic	B-Device
digital	I-Device
computer	I-Device
introduced	O
in	O
1960	O
by	O
the	O
Monroe	O
Calculating	O
Machine	O
Division	O
of	O
Litton	O
Industries	O
.	O
</s>
<s>
Upon	O
introduction	O
in	O
May	O
1960	O
,	O
the	O
Monrobot	B-Device
XI	I-Device
sold	O
for	O
US$	O
24,500	O
.	O
</s>
<s>
The	O
manufacturer	O
also	O
marketed	O
other	O
computer	O
systems	O
in	O
the	O
family	O
,	O
such	O
as	O
the	O
Monrobot	O
IX	O
and	O
Monrobot	O
MU	O
,	O
but	O
the	O
Monrobot	B-Device
XI	I-Device
appeared	O
to	O
be	O
the	O
most	O
popular	O
model	O
.	O
</s>
<s>
The	O
bare-bones	O
Monrobot	B-Device
XI	I-Device
resembled	O
an	O
ordinary	O
steel	O
desk	O
in	O
length	O
,	O
breadth	O
,	O
and	O
height	O
,	O
surmounted	O
by	O
an	O
ordinary	O
typewriter	O
and	O
a	O
breadbox-sized	O
control	O
panel	O
with	O
indicator	O
lights	O
and	O
switches	O
.	O
</s>
<s>
Unlike	O
virtually	O
all	O
electronic	B-Device
digital	I-Device
computers	I-Device
ever	O
built	O
,	O
as	O
an	O
early	O
machine	O
,	O
the	O
Monrobot	B-Device
XI	I-Device
was	O
one	O
of	O
the	O
small	O
family	O
of	O
computers	O
which	O
totally	O
lacked	O
random-access	B-Architecture
memory	I-Architecture
(	O
RAM	B-Architecture
)	O
,	O
an	O
alternative	O
tecnhnology	O
which	O
would	O
have	O
allowed	O
it	O
to	O
access	O
all	O
memory	O
words	O
equally	O
rapidly	O
.	O
</s>
<s>
Even	O
at	O
the	O
time	O
it	O
was	O
introduced	O
,	O
it	O
was	O
not	O
rare	O
for	O
electronic	B-Device
digital	I-Device
computers	I-Device
to	O
use	O
magnetic-core	O
memory	O
for	O
RAM	B-Architecture
;	O
the	O
price	O
(	O
per	O
bit	O
)	O
of	O
which	O
would	O
eventually	O
fall	O
from	O
over	O
US$1	O
in	O
the	O
early	O
1950s	O
to	O
about	O
US	O
$0.20	O
by	O
the	O
mid-1960s	O
.	O
</s>
<s>
Instead	O
to	O
keep	O
the	O
cost	O
of	O
the	O
machine	O
very	O
low	O
,	O
the	O
Monorobot	O
XI	O
used	O
a	O
form	O
of	O
memory	O
in	O
which	O
words	O
were	O
only	O
periodically	O
accessible	O
in	O
sequential	O
order	O
,	O
via	O
an	O
electromechanical	O
moving	O
device	O
called	O
magnetic	B-General_Concept
drum	I-General_Concept
memory	I-General_Concept
.	O
</s>
<s>
The	O
long	O
latency	O
of	O
memory	O
access	O
,	O
which	O
followed	O
from	O
exclusive	O
reliance	O
on	O
a	O
macroscopic	O
moving	O
part	O
,	O
made	O
the	O
Monrobot	B-Device
XI	I-Device
operate	O
very	O
slowly	O
,	O
despite	O
the	O
use	O
of	O
non-mechanical	O
electronics	O
for	O
logical	O
functions	O
.	O
</s>
<s>
The	O
Monorobot	O
XI	O
might	O
best	O
be	O
thought	O
of	O
as	O
a	O
modernized	O
(	O
solid-state	O
)	O
,	O
low	O
cost	O
version	O
of	O
the	O
IBM	B-Device
650	I-Device
,	O
which	O
had	O
been	O
the	O
world	O
's	O
first	O
mass-produced	O
computer	O
,	O
leased	O
at	O
US$	O
3,250	O
per	O
month	O
,	O
almost	O
800	O
of	O
which	O
were	O
made	O
between	O
1954	O
and	O
1958	O
,	O
a	O
total	O
of	O
2000	O
by	O
1962	O
.	O
</s>
<s>
Both	O
the	O
IBM	B-Device
650	I-Device
and	O
Monrobot	B-Device
XI	I-Device
used	O
a	O
magnetic	B-General_Concept
drum	I-General_Concept
for	O
primary	O
memory	O
,	O
but	O
the	O
former	O
used	O
vacuum	O
tubes	O
and	O
bi-quinary	O
coding	O
,	O
rather	O
than	O
transistors	B-Application
and	O
binary	O
coding	O
,	O
for	O
its	O
electronics	O
.	O
</s>
<s>
The	O
Monrobot	B-Device
XI	I-Device
's	O
rewritable	O
,	O
persistent	O
(	O
"	O
nonvolatile	O
"	O
)	O
memory	O
consisted	O
of	O
a	O
rotating	O
magnetic	B-General_Concept
drum	I-General_Concept
storing	O
1,024	O
words	O
of	O
32	O
bits	O
,	O
each	O
of	O
which	O
could	O
record	O
either	O
a	O
single	O
integer	O
,	O
or	O
a	O
pair	O
of	O
zero	O
-	O
or	O
single-address	O
instructions	O
.	O
</s>
<s>
Even	O
the	O
8	O
"	O
high-speed	O
"	O
registers	O
of	O
the	O
central	B-General_Concept
processing	I-General_Concept
unit	I-General_Concept
(	O
CPU	O
)	O
physically	O
resided	O
on	O
the	O
drum	O
,	O
in	O
two	O
dedicated	O
tracks	O
,	O
but	O
by	O
being	O
replicated	O
16	O
times	O
(	O
with	O
16	O
times	O
as	O
many	O
read/write	B-Device
heads	I-Device
heads	O
distributed	O
around	O
the	O
drum	O
periphery	O
)	O
,	O
they	O
could	O
be	O
read	O
or	O
written	O
16	O
times	O
as	O
fast	O
as	O
the	O
bulk	O
of	O
persistent	O
memory	O
.	O
</s>
<s>
A	O
perforated	O
metal	O
screen	O
at	O
the	O
side	O
or	O
back	O
of	O
the	O
cabinet	O
could	O
be	O
removed	O
,	O
affording	O
a	O
direct	O
view	O
of	O
the	O
reddish-brown	O
iron-oxide-coated	O
drum	O
,	O
surrounded	O
by	O
multiple	O
stationary	O
magnetic	O
read/write	B-Device
heads	I-Device
.	O
</s>
<s>
There	O
was	O
no	O
special	O
provision	O
for	O
protection	O
from	O
dust	O
,	O
as	O
the	O
magnetic	O
heads	O
were	O
rigidly	O
mounted	O
at	O
fixed	O
distances	O
from	O
the	O
magnetic	O
surface	O
,	O
and	O
did	O
not	O
use	O
"	O
flying	B-Device
head	I-Device
"	O
technology	O
.	O
</s>
<s>
Except	O
for	O
neon	O
lamps	O
in	O
the	O
control	O
panel	O
and	O
10	O
to	O
30	O
blue-green	O
electroluminescent	O
lamp	O
vacuum	O
tubes	O
employed	O
for	O
output	O
displays	O
in	O
later	O
versions	O
,	O
the	O
electronics	O
used	O
only	O
discrete	O
solid-state	O
components	O
,	O
including	O
383	O
transistors	B-Application
(	O
mostly	O
2N412	O
)	O
and	O
2,300	O
diodes	O
(	O
mostly	O
1N636	O
)	O
.	O
</s>
<s>
The	O
arithmetic	O
unit	O
alone	O
used	O
190	O
transistors	B-Application
and	O
1,675	O
diodes	O
.	O
</s>
<s>
This	O
astoundingly	O
small	O
active	O
component	O
count	O
(	O
383	O
)	O
-	O
little	O
more	O
than	O
in	O
the	O
Manchester	B-Device
Baby	I-Device
(	O
250	O
)	O
,	O
the	O
world	O
's	O
first	O
(	O
1948	O
)	O
stored-program	O
Turing-complete	O
computer	O
–	O
contrasts	O
starkly	O
with	O
the	O
many	O
billions	O
of	O
transistors	B-Application
present	O
in	O
modern	O
microprocessors	B-Architecture
used	O
in	O
handheld	O
cellphones	O
.	O
</s>
<s>
The	O
low	O
component	O
count	O
was	O
a	O
key	O
benefit	O
of	O
its	O
slow	O
electromechanical	O
memory	O
,	O
which	O
exploited	O
synchronization	O
with	O
a	O
spinning	O
drum	O
's	O
rotational	O
angle	O
,	O
rather	O
than	O
adding	O
electronic	O
switches	O
,	O
to	O
accomplish	O
multiplexing	B-Architecture
of	O
bits	O
.	O
</s>
<s>
For	O
comparison	O
,	O
even	O
Intel	O
's	O
first	O
(	O
1971	O
)	O
microprocessor	B-Architecture
,	O
the	O
four-bit	O
Intel	B-General_Concept
4004	I-General_Concept
,	O
required	O
about	O
2,300	O
transistors	B-Application
in	O
its	O
monolithic	O
design	O
.	O
</s>
<s>
This	O
continued	O
an	O
electronics	O
construction	O
tradition	O
pioneered	O
when	O
the	O
relatively	O
unreliable	O
vacuum	O
tubes	O
had	O
been	O
used	O
as	O
active	O
components	O
,	O
prior	O
to	O
the	O
advance	O
to	O
more	O
modern	O
transistors	B-Application
used	O
in	O
the	O
Monorobot	O
XI	O
.	O
</s>
<s>
Unlike	O
vacuum	O
tubes	O
,	O
which	O
were	O
always	O
plugged	O
into	O
sockets	O
,	O
discrete	O
transistors	B-Application
were	O
often	O
permanently	O
soldered	O
into	O
place	O
.	O
</s>
<s>
Division	O
(	O
500	O
ms	O
)	O
and	O
more-advanced	O
floating-point	B-Algorithm
functions	O
were	O
implemented	O
in	O
software	O
.	O
</s>
<s>
A	O
total	O
of	O
27	O
machine	O
opcode	B-Language
instructions	O
were	O
defined	O
.	O
</s>
<s>
The	O
computer	O
could	O
be	O
programmed	O
using	O
an	O
assembly	B-Language
language	I-Language
system	O
called	O
QUIKOMP	O
,	O
but	O
its	O
simple	O
machine	O
language	O
instruction	O
set	O
and	O
slow	O
operation	O
speed	O
encouraged	O
many	O
programmers	O
to	O
code	O
directly	O
in	O
numeric	B-Algorithm
opcodes	B-Language
.	O
</s>
<s>
A	O
reference	B-General_Concept
card	I-General_Concept
was	O
available	O
to	O
help	O
in	O
remembering	O
the	O
numeric	B-Algorithm
opcodes	B-Language
and	O
data	O
codes	O
.	O
</s>
<s>
Bits	O
were	O
idiosyncratically	O
numbered	B-Language
on	O
the	O
control	O
panel	O
from	O
16	O
(	O
MSB	O
,	O
leftmost	O
)	O
down	O
to	O
1	O
(	O
LSB	O
,	O
rightmost	O
)	O
,	O
although	O
the	O
programmer	O
's	O
manual	O
numbered	B-Language
them	O
from	O
15	O
to	O
0	O
in	O
a	O
more	O
standard	O
manner	O
.	O
</s>
<s>
The	O
minimal	O
loader	B-Operating_System
program	O
had	O
no	O
provisions	O
to	O
support	O
multiple	O
users	O
on	O
a	O
single	O
machine	O
.	O
</s>
<s>
To	O
accommodate	O
multiple	O
users	O
economically	O
,	O
time-consuming	O
manual	O
data	O
entry	O
could	O
be	O
performed	O
offline	O
,	O
by	O
use	O
of	O
several	O
separate	O
key-to-punch	O
papertape	O
machines	O
(	O
called	O
"	O
add-punch	O
"	O
machines	O
)	O
,	O
whose	O
numeric-only	O
keyboards	O
were	O
slightly-modified	O
versions	O
of	O
mechanical	O
desk	O
calculators	O
.	O
</s>
<s>
Because	O
the	O
mechanical	O
calculator-style	O
keyboards	O
could	O
only	O
generate	O
decimal	O
(	O
base	O
10	O
)	O
codes	O
,	O
the	O
numerical	O
opcodes	B-Language
were	O
specified	O
in	O
decimal	O
,	O
even	O
though	O
the	O
actual	O
processing	O
was	O
in	O
binary	O
.	O
</s>
<s>
Experienced	O
programmers	O
soon	O
learned	O
to	O
read	O
the	O
numeric	B-Algorithm
codes	O
visually	O
from	O
the	O
punched	O
paper	O
tapes	O
.	O
</s>
<s>
When	O
an	O
"	O
add-punch	O
"	O
tape	O
had	O
been	O
proofread	O
and	O
corrected	O
,	O
it	O
was	O
ready	O
for	O
loading	O
via	O
a	O
paper	O
tape	O
reader	O
into	O
the	O
Monrobot	B-Device
XI	I-Device
for	O
execution	O
and	O
debugging	O
.	O
</s>
<s>
The	O
console	B-General_Concept
terminal	I-General_Concept
typically	O
was	O
a	O
modified	O
IBM	O
typewriter	O
.	O
</s>
<s>
An	O
option	O
was	O
a	O
heavy-duty	O
Flexowriter	B-Application
,	O
which	O
rattled	O
and	O
shook	O
the	O
entire	O
machine	O
,	O
especially	O
when	O
the	O
heavy	O
carriage	O
forcefully	O
returned	O
to	O
the	O
beginning	O
of	O
a	O
new	O
print	O
line	O
.	O
</s>
<s>
An	O
80-column	O
punched	B-Architecture
card	I-Architecture
reader/punch	O
could	O
optionally	O
be	O
added	O
to	O
the	O
base	O
configuration	O
.	O
</s>
<s>
An	O
episode	O
of	O
the	O
animated	O
television	O
series	O
Futurama	B-Application
,	O
originally	O
airing	O
in	O
2001	O
,	O
featured	O
a	O
humanoid	O
robot	O
resembling	O
mid-20th	O
century	O
sex	O
symbol	O
Marilyn	O
Monroe	O
,	O
named	O
"	O
Marilyn	O
Monrobot	O
"	O
,	O
as	O
a	O
character	O
within	O
a	O
film	O
viewed	O
by	O
the	O
episode	O
cast	O
.	O
</s>
