<s>
The	O
Automatic	B-Device
Computing	I-Device
Engine	I-Device
(	O
ACE	B-Device
)	O
was	O
a	O
British	O
early	O
electronic	B-General_Concept
serial	B-Device
stored-program	O
computer	O
design	O
by	O
Alan	O
Turing	O
.	O
</s>
<s>
Turing	O
completed	O
the	O
ambitious	O
design	O
in	O
late	O
1945	O
,	O
having	O
had	O
experience	O
in	O
the	O
years	O
prior	O
with	O
the	O
secret	O
Collossus	B-Device
computer	O
at	O
Bletchley	O
Park	O
.	O
</s>
<s>
The	O
ACE	B-Device
was	O
not	O
built	O
,	O
but	O
a	O
smaller	O
version	O
,	O
the	O
Pilot	B-Device
ACE	I-Device
,	O
was	O
constructed	O
at	O
the	O
National	O
Physical	O
Laboratory	O
and	O
became	O
operational	O
in	O
1950	O
.	O
</s>
<s>
A	O
larger	O
implementation	O
of	O
the	O
ACE	B-Device
design	O
was	O
the	O
MOSAIC	O
computer	O
which	O
became	O
operational	O
in	O
1955	O
.	O
</s>
<s>
ACE	B-Device
also	O
led	O
to	O
the	O
Bendix	B-Device
G-15	I-Device
and	O
other	O
computers	O
.	O
</s>
<s>
The	O
use	O
of	O
the	O
word	O
Engine	O
was	O
in	O
homage	O
to	O
Charles	O
Babbage	O
and	O
his	O
Difference	O
Engine	O
and	O
Analytical	B-Device
Engine	I-Device
.	O
</s>
<s>
Turing	O
's	O
technical	O
design	O
Proposed	O
Electronic	B-General_Concept
Calculator	O
was	O
the	O
product	O
of	O
his	O
theoretical	O
work	O
in	O
1936	O
"	O
On	O
Computable	O
Numbers	O
"	O
and	O
his	O
wartime	O
experience	O
at	O
Bletchley	O
Park	O
where	O
the	O
Colossus	B-Device
computers	I-Device
had	O
been	O
successful	O
in	O
breaking	O
German	O
military	O
codes	O
.	O
</s>
<s>
Turing	O
was	O
sought	O
by	O
Womersley	O
to	O
work	O
in	O
the	O
NPL	O
on	O
the	O
ACE	B-Device
project	O
;	O
he	O
accepted	O
and	O
began	O
work	O
on	O
1	O
October	O
1945	O
and	O
by	O
the	O
end	O
of	O
the	O
year	O
he	O
completed	O
his	O
outline	O
of	O
his	O
'	O
Proposed	O
electronic	B-General_Concept
calculator	O
 '	O
,	O
which	O
was	O
the	O
first	O
reasonably	O
complete	O
design	O
of	O
a	O
stored-program	O
computer	O
and	O
,	O
apart	O
from	O
being	O
on	O
a	O
much	O
larger	O
scale	O
than	O
the	O
final	O
working	O
machine	O
,	O
anticipated	O
the	O
final	O
realisation	O
in	O
most	O
important	O
respects	O
.	O
</s>
<s>
However	O
,	O
because	O
of	O
the	O
strict	O
and	O
long-lasting	O
secrecy	O
around	O
the	O
Bletchley	O
Park	O
work	O
,	O
he	O
was	O
prohibited	O
(	O
because	O
of	O
the	O
Official	O
Secrets	O
Act	O
)	O
from	O
explaining	O
that	O
he	O
knew	O
that	O
his	O
ideas	O
could	O
be	O
implemented	O
in	O
an	O
electronic	B-General_Concept
device	O
.	O
</s>
<s>
The	O
better-known	O
EDVAC	B-Device
design	O
presented	O
in	O
the	O
First	O
Draft	O
of	O
a	O
Report	O
on	O
the	O
EDVAC	B-Device
(	O
dated	O
30	O
June	O
1945	O
)	O
,	O
by	O
John	O
von	O
Neumann	O
,	O
who	O
knew	O
of	O
Turing	O
's	O
theoretical	O
work	O
,	O
received	O
much	O
publicity	O
,	O
despite	O
its	O
incomplete	O
nature	O
and	O
questionable	O
lack	O
of	O
attribution	O
of	O
the	O
sources	O
of	O
some	O
of	O
the	O
ideas	O
.	O
</s>
<s>
Turing	O
's	O
report	O
on	O
the	O
ACE	B-Device
was	O
written	O
in	O
late	O
1945	O
and	O
included	O
detailed	O
logical	O
circuit	O
diagrams	O
and	O
a	O
cost	O
estimate	O
of	O
£	O
11,200	O
.	O
</s>
<s>
He	O
felt	O
that	O
speed	O
and	O
size	O
of	O
memory	B-General_Concept
were	O
crucial	O
and	O
he	O
proposed	O
a	O
high-speed	O
memory	B-General_Concept
of	O
what	O
would	O
today	O
be	O
called	O
25	O
kilobytes	O
,	O
accessed	O
at	O
a	O
speed	O
of	O
1	O
MHz	O
;	O
he	O
remarked	O
that	O
for	O
the	O
purposes	O
required	O
"	O
the	O
memory	B-General_Concept
needs	O
to	O
be	O
very	O
large	O
indeed	O
by	O
comparison	O
with	O
standards	O
which	O
prevail	O
in	O
most	O
valve	O
and	O
relay	O
work	O
,	O
and	O
 [ so ] 	O
it	O
is	O
necessary	O
to	O
look	O
for	O
some	O
more	O
economical	O
form	O
of	O
storage	O
"	O
,	O
and	O
that	O
memory	B-General_Concept
"	O
appears	O
to	O
be	O
the	O
main	O
limitation	O
in	O
the	O
design	O
of	O
a	O
calculator	O
,	O
i.e.	O
</s>
<s>
The	O
ACE	B-Device
implemented	O
subroutine	O
calls	O
,	O
whereas	O
the	O
EDVAC	B-Device
did	O
not	O
,	O
and	O
what	O
also	O
set	O
the	O
ACE	B-Device
apart	O
from	O
the	O
EDVAC	B-Device
was	O
the	O
use	O
of	O
Abbreviated	O
Computer	O
Instructions	O
,	O
an	O
early	O
form	O
of	O
programming	O
language	O
.	O
</s>
<s>
Initially	O
,	O
it	O
was	O
planned	O
that	O
Tommy	O
Flowers	O
,	O
the	O
engineer	O
at	O
the	O
Post	O
Office	O
Research	O
Station	O
at	O
Dollis	O
Hill	O
in	O
north	O
London	O
,	O
who	O
had	O
been	O
responsible	O
for	O
building	O
the	O
Colossus	B-Device
computers	I-Device
should	O
build	O
the	O
ACE	B-Device
,	O
but	O
because	O
of	O
the	O
secrecy	O
around	O
his	O
wartime	O
achievements	O
and	O
the	O
pressure	O
of	O
post-war	O
work	O
,	O
this	O
was	O
not	O
possible	O
.	O
</s>
<s>
Turing	O
's	O
colleagues	O
at	O
the	O
NPL	O
,	O
not	O
knowing	O
about	O
Colossus	B-Device
,	O
thought	O
that	O
the	O
engineering	O
work	O
to	O
build	O
a	O
complete	O
ACE	B-Device
was	O
too	O
ambitious	O
,	O
so	O
the	O
first	O
version	O
of	O
the	O
ACE	B-Device
that	O
was	O
built	O
was	O
the	O
Pilot	B-Device
Model	I-Device
ACE	I-Device
,	O
a	O
smaller	O
version	O
of	O
Turing	O
's	O
original	O
design	O
.	O
</s>
<s>
Turing	O
's	O
assistant	O
,	O
Jim	O
Wilkinson	O
,	O
worked	O
on	O
the	O
logical	O
design	O
of	O
the	O
ACE	B-Device
and	O
after	O
Turing	O
left	O
for	O
Cambridge	O
in	O
1947	O
,	O
Wilkinson	O
was	O
appointed	O
to	O
lead	O
the	O
ACE	B-Device
group	O
.	O
</s>
<s>
The	O
Pilot	B-Device
ACE	I-Device
had	O
fewer	O
than	O
1000	O
thermionic	O
valves	O
(	O
vacuum	O
tubes	O
)	O
compared	O
to	O
about	O
18,000	O
in	O
the	O
ENIAC	B-Device
.	O
</s>
<s>
It	O
used	O
mercury	O
delay	O
lines	O
for	O
its	O
main	O
memory	B-General_Concept
.	O
</s>
<s>
The	O
first	O
production	O
versions	O
of	O
the	O
Pilot	B-Device
ACE	I-Device
,	O
the	O
English	B-Device
Electric	I-Device
DEUCE	I-Device
,	O
of	O
which	O
31	O
were	O
sold	O
,	O
were	O
delivered	O
in	O
1955	O
.	O
</s>
<s>
A	O
second	O
implementation	O
of	O
the	O
ACE	B-Device
design	O
was	O
the	O
MOSAIC	O
(	O
Ministry	O
of	O
Supply	O
Automatic	O
Integrator	O
and	O
Computer	O
)	O
.	O
</s>
<s>
This	O
was	O
built	O
by	O
Allen	O
Coombs	O
and	O
William	O
Chandler	O
of	O
Dollis	O
Hill	O
who	O
had	O
worked	O
with	O
Tommy	O
Flowers	O
on	O
building	O
the	O
ten	O
Colossus	B-Device
computers	I-Device
.	O
</s>
<s>
MOSAIC	O
contained	O
6,480	O
electronic	B-General_Concept
valves	O
and	O
had	O
an	O
availability	O
of	O
about	O
75%	O
.	O
</s>
<s>
The	O
principles	O
of	O
the	O
ACE	B-Device
design	O
were	O
used	O
in	O
the	O
Bendix	O
Corporation	O
's	O
G-15	B-Device
computer	O
.	O
</s>
<s>
The	O
engineering	O
design	O
was	O
done	O
by	O
Harry	O
Huskey	O
who	O
had	O
spent	O
1947	O
in	O
the	O
ACE	B-Device
section	O
at	O
the	O
NPL	O
.	O
</s>
<s>
He	O
later	O
contributed	O
to	O
the	O
hardware	O
designs	O
for	O
the	O
EDVAC	B-Device
.	O
</s>
<s>
The	O
first	O
G-15	B-Device
ran	O
in	O
1954	O
and	O
,	O
as	O
a	O
relatively	O
small	O
single-user	O
machine	O
,	O
some	O
consider	O
it	O
to	O
be	O
the	O
first	O
personal	B-Device
computer	I-Device
.	O
</s>
<s>
Other	O
derivatives	O
of	O
the	O
ACE	B-Device
include	O
the	O
EMI	O
Electronic	B-General_Concept
Business	O
Machine	O
and	O
the	O
Packard	O
Bell	O
Corporation	O
PB	B-Device
250	I-Device
.	O
</s>
