<s>
The	O
Harvard	B-Device
Mark	I-Device
I	I-Device
,	O
or	O
IBM	B-Device
Automatic	I-Device
Sequence	I-Device
Controlled	I-Device
Calculator	I-Device
(	O
ASCC	O
)	O
,	O
was	O
a	O
general-purpose	O
electromechanical	O
computer	O
used	O
in	O
the	O
war	O
effort	O
during	O
the	O
last	O
part	O
of	O
World	O
War	O
II	O
.	O
</s>
<s>
One	O
of	O
the	O
first	O
programs	O
to	O
run	O
on	O
the	O
Mark	O
I	O
was	O
initiated	O
on	O
29	O
March	O
1944	O
by	O
John	O
von	B-Architecture
Neumann	I-Architecture
.	O
</s>
<s>
At	O
that	O
time	O
,	O
von	B-Architecture
Neumann	I-Architecture
was	O
working	O
on	O
the	O
Manhattan	O
Project	O
,	O
and	O
needed	O
to	O
determine	O
whether	O
implosion	O
was	O
a	O
viable	O
choice	O
to	O
detonate	O
the	O
atomic	O
bomb	O
that	O
would	O
be	O
used	O
a	O
year	O
later	O
.	O
</s>
<s>
The	O
Mark	O
I	O
also	O
computed	O
and	O
printed	O
mathematical	O
tables	O
,	O
which	O
had	O
been	O
the	O
initial	O
goal	O
of	O
British	O
inventor	O
Charles	O
Babbage	O
for	O
his	O
"	O
analytical	B-Device
engine	I-Device
"	O
in	O
1837	O
.	O
</s>
<s>
This	O
led	O
him	O
to	O
study	O
Babbage	O
and	O
to	O
add	O
references	O
of	O
the	B-Device
Analytical	I-Device
Engine	I-Device
to	O
his	O
proposal	O
;	O
the	O
resulting	O
machine	O
"	O
brought	O
Babbage	O
’s	O
principles	O
of	O
the	B-Device
Analytical	I-Device
Engine	I-Device
almost	O
to	O
full	O
realization	O
,	O
while	O
adding	O
important	O
new	O
features.	O
"	O
</s>
<s>
The	O
Automatic	B-Device
Sequence	I-Device
Controlled	I-Device
Calculator	I-Device
(	O
Harvard	B-Device
Mark	I-Device
I	I-Device
)	O
was	O
the	O
first	O
operating	O
machine	O
that	O
could	O
execute	O
long	O
computations	O
automatically	O
.	O
</s>
<s>
It	O
executed	O
the	O
current	O
instruction	B-General_Concept
and	O
then	O
read	O
in	O
the	O
next	O
one	O
.	O
</s>
<s>
Instructions	O
could	O
not	O
be	O
executed	O
from	O
the	O
storage	O
registers	B-General_Concept
.	O
</s>
<s>
This	O
separation	O
of	O
data	O
and	O
instructions	O
is	O
known	O
as	O
the	O
Harvard	B-Architecture
architecture	I-Architecture
(	O
although	O
the	O
exact	O
nature	O
of	O
this	O
separation	O
that	O
makes	O
a	O
machine	O
Harvard	O
,	O
rather	O
than	O
Von	B-Architecture
Neumann	I-Architecture
,	O
has	O
been	O
obscured	O
with	O
the	O
passage	O
of	O
time	O
;	O
see	O
Modified	B-Device
Harvard	I-Device
architecture	I-Device
)	O
.	O
</s>
<s>
A	O
program	O
loop	O
was	O
accomplished	O
by	O
loop	B-Operating_System
unrolling	I-Operating_System
or	O
by	O
joining	O
the	O
end	O
of	O
the	O
paper	O
tape	O
containing	O
the	O
program	O
back	O
to	O
the	O
beginning	O
of	O
the	O
tape	O
(	O
literally	O
creating	O
a	O
loop	O
)	O
.	O
</s>
<s>
Each	O
storage	O
location	O
,	O
each	O
set	O
of	O
switches	O
,	O
and	O
the	O
registers	B-General_Concept
associated	O
with	O
the	O
input	B-General_Concept
,	I-General_Concept
output	I-General_Concept
,	O
and	O
arithmetic	B-General_Concept
units	I-General_Concept
were	O
assigned	O
a	O
unique	O
identifying	O
index	O
number	O
.	O
</s>
<s>
The	O
first	O
field	O
was	O
the	O
binary	O
index	O
of	O
the	O
result	O
of	O
the	O
operation	O
,	O
the	O
second	O
was	O
the	O
source	O
datum	B-General_Concept
for	O
the	O
operation	O
and	O
the	O
third	O
field	O
was	O
a	O
code	B-Language
for	O
the	O
operation	O
to	O
be	O
performed	O
.	O
</s>
<s>
John	O
von	B-Architecture
Neumann	I-Architecture
had	O
a	O
team	O
at	O
Los	O
Alamos	O
that	O
used	O
"	O
modified	O
IBM	O
punched-card	O
machines	O
"	O
to	O
determine	O
the	O
effects	O
of	O
implosion	O
.	O
</s>
<s>
"	O
Von	B-Architecture
Neumann	I-Architecture
joined	O
the	O
Manhattan	O
Project	O
in	O
1943	O
,	O
working	O
on	O
the	O
immense	O
number	O
of	O
calculations	O
needed	O
to	O
build	O
the	O
atomic	O
bomb	O
.	O
</s>
<s>
Aiken	O
,	O
in	O
turn	O
,	O
decided	O
to	O
build	O
further	O
machines	O
without	O
IBM	O
’s	O
help	O
,	O
and	O
the	O
ASCC	O
came	O
to	O
be	O
generally	O
known	O
as	O
the	O
"	O
Harvard	B-Device
Mark	I-Device
I	I-Device
"	O
.	O
</s>
<s>
IBM	O
went	O
on	O
to	O
build	O
its	O
Selective	B-Device
Sequence	I-Device
Electronic	I-Device
Calculator	I-Device
(	O
SSEC	O
)	O
to	O
both	O
test	O
new	O
technology	O
and	O
provide	O
more	O
publicity	O
for	O
the	O
company	O
's	O
own	O
efforts	O
.	O
</s>
<s>
The	O
Mark	O
I	O
was	O
followed	O
by	O
the	O
Harvard	B-Device
Mark	I-Device
II	I-Device
(	O
1947	O
or	O
1948	O
)	O
,	O
Mark	B-Device
III/ADEC	I-Device
(	O
September	O
1949	O
)	O
,	O
and	O
Harvard	B-Device
Mark	I-Device
IV	I-Device
(	O
1952	O
)	O
–	O
all	O
the	O
work	O
of	O
Aiken	O
.	O
</s>
<s>
The	O
Mark	O
III	O
used	O
mostly	O
electronic	O
components	O
—	O
vacuum	O
tubes	O
and	O
crystal	O
diodes	O
—	O
but	O
also	O
included	O
mechanical	O
components	O
:	O
rotating	O
magnetic	B-General_Concept
drums	I-General_Concept
for	O
storage	O
,	O
plus	O
relays	O
for	O
transferring	O
data	O
between	O
drums	O
.	O
</s>
