<s>
The	O
Z3	B-Device
was	O
a	O
German	O
electromechanical	O
computer	O
designed	O
by	O
Konrad	O
Zuse	O
in	O
1938	O
,	O
and	O
completed	O
in	O
1941	O
.	O
</s>
<s>
It	O
was	O
the	O
world	O
's	O
first	O
working	O
programmable	B-General_Concept
,	O
fully	O
automatic	O
digital	O
computer	O
.	O
</s>
<s>
The	O
Z3	B-Device
was	O
built	O
with	O
2,600	O
relays	O
,	O
implementing	O
a	O
22-bit	O
word	O
length	O
that	O
operated	O
at	O
a	O
clock	O
frequency	O
of	O
about	O
5	O
–	O
10Hz	O
.	O
</s>
<s>
Program	O
code	O
was	O
stored	O
on	O
punched	O
film	B-Language
.	O
</s>
<s>
The	O
Z3	B-Device
was	O
completed	O
in	O
Berlin	O
in	O
1941	O
.	O
</s>
<s>
The	O
original	O
Z3	B-Device
was	O
destroyed	O
on	O
21	O
December	O
1943	O
during	O
an	O
Allied	O
bombardment	O
of	O
Berlin	O
.	O
</s>
<s>
That	O
Z3	B-Device
was	O
originally	O
called	O
V3	O
(	O
Versuchsmodell	O
3	O
or	O
Experimental	O
Model	O
3	O
)	O
but	O
was	O
renamed	O
so	O
that	O
it	O
would	O
not	O
be	O
confused	O
with	O
Germany	O
's	O
V-weapons	O
.	O
</s>
<s>
The	O
Z3	B-Device
was	O
demonstrated	O
in	O
1998	O
to	O
be	O
,	O
in	O
principle	O
,	O
Turing-complete	O
.	O
</s>
<s>
However	O
,	O
because	O
it	O
lacked	O
conditional	B-Language
branching	I-Language
,	O
the	O
Z3	B-Device
only	O
meets	O
this	O
definition	O
by	O
speculatively	O
computing	O
all	O
possible	O
outcomes	O
of	O
a	O
calculation	O
.	O
</s>
<s>
Zuse	O
designed	O
the	O
Z1	B-Device
in	O
1935	O
to	O
1936	O
and	O
built	O
it	O
from	O
1936	O
to	O
1938	O
.	O
</s>
<s>
The	O
Z1	B-Device
was	O
wholly	O
mechanical	O
and	O
only	O
worked	O
for	O
a	O
few	O
minutes	O
at	O
a	O
time	O
at	O
most	O
.	O
</s>
<s>
As	O
a	O
doctoral	O
student	O
at	O
the	O
Berlin	O
Institute	O
of	O
Technology	O
in	O
1937	O
he	O
worked	O
on	O
the	O
implementation	O
of	O
Boolean	O
operations	O
and	O
(	O
in	O
today	O
's	O
terminology	O
)	O
flip-flops	B-General_Concept
on	O
the	O
basis	O
of	O
vacuum	O
tubes	O
.	O
</s>
<s>
The	O
realization	O
of	O
the	O
Z2	B-Device
was	O
helped	O
financially	O
by	O
Kurt	O
Pannke	O
,	O
who	O
manufactured	O
small	O
calculating	O
machines	O
.	O
</s>
<s>
The	O
Z2	B-Device
was	O
completed	O
and	O
presented	O
to	O
an	O
audience	O
of	O
the	O
(	O
"	O
German	O
Laboratory	O
for	O
Aviation	O
"	O
)	O
in	O
1940	O
in	O
Berlin-Adlershof	O
.	O
</s>
<s>
Zuse	O
was	O
lucky	O
–	O
this	O
presentation	O
was	O
one	O
of	O
the	O
few	O
instances	O
where	O
the	O
Z2	B-Device
actually	O
worked	O
and	O
could	O
convince	O
the	O
DVL	O
to	O
partly	O
finance	O
the	O
next	O
design	O
.	O
</s>
<s>
Improving	O
on	O
the	O
basic	O
Z2	B-Device
machine	O
,	O
he	O
built	O
the	O
Z3	B-Device
in	O
1941	O
,	O
which	O
was	O
a	O
highly	O
secret	O
project	O
of	O
the	O
German	O
government	O
.	O
</s>
<s>
The	O
Z3	B-Device
was	O
completed	O
in	O
1941	O
and	O
was	O
faster	O
and	O
far	O
more	O
reliable	O
than	O
the	O
Z1	B-Device
and	O
Z2	B-Device
.	O
</s>
<s>
The	O
Z3	B-Device
floating-point	B-Algorithm
arithmetic	I-Algorithm
was	O
improved	O
over	O
that	O
of	O
the	O
Z1	B-Device
in	O
that	O
it	O
implemented	O
exception	O
handling	O
"	O
using	O
just	O
a	O
few	O
relays	O
"	O
,	O
the	O
exceptional	O
values	O
(	O
plus	O
infinity	O
,	O
minus	O
infinity	O
and	O
undefined	O
)	O
could	O
be	O
generated	O
and	O
passed	O
through	O
operations	O
.	O
</s>
<s>
The	O
Z3	B-Device
,	O
like	O
its	O
predecessors	O
,	O
stored	O
its	O
program	O
on	O
an	O
external	O
punched	O
tape	O
,	O
thus	O
no	O
rewiring	O
was	O
necessary	O
to	O
change	O
programs	O
.	O
</s>
<s>
However	O
,	O
it	O
did	O
not	O
have	O
conditional	B-Language
branching	I-Language
found	O
in	O
later	O
universal	B-Architecture
computers	I-Architecture
.	O
</s>
<s>
On	O
12	O
May	O
1941	O
,	O
the	O
Z3	B-Device
was	O
presented	O
to	O
an	O
audience	O
of	O
scientists	O
including	O
the	O
professors	O
Alfred	O
Teichmann	O
and	O
Curt	O
Schmieden	O
of	O
the	O
(	O
"	O
German	O
Laboratory	O
for	O
Aviation	O
"	O
)	O
in	O
Berlin	O
,	O
today	O
known	O
as	O
the	O
German	O
Aerospace	O
Center	O
in	O
Cologne	O
.	O
</s>
<s>
Zuse	O
moved	O
on	O
to	O
the	O
Z4	B-Device
design	O
,	O
which	O
he	O
completed	O
in	O
a	O
bunker	O
in	O
the	O
Harz	O
mountains	O
,	O
alongside	O
Wernher	O
von	O
Braun	O
's	O
ballistic	O
missile	O
development	O
.	O
</s>
<s>
When	O
World	O
War	O
II	O
ended	O
,	O
Zuse	O
retreated	O
to	O
Hinterstein	O
in	O
the	O
Alps	O
with	O
the	O
Z4	B-Device
,	O
where	O
he	O
remained	O
for	O
several	O
years	O
.	O
</s>
<s>
The	O
Z3	B-Device
operated	O
as	O
a	O
stack	B-Application
machine	I-Application
with	O
a	O
stack	O
of	O
two	O
registers	O
,	O
R1	O
and	O
R2	O
.	O
</s>
<s>
It	O
was	O
possible	O
to	O
construct	O
loops	O
on	O
the	O
Z3	B-Device
,	O
but	O
there	O
was	O
no	O
conditional	B-General_Concept
branch	I-General_Concept
instruction	O
.	O
</s>
<s>
Nevertheless	O
,	O
the	O
Z3	B-Device
was	O
Turing-complete	O
–	O
how	O
to	O
implement	O
a	O
universal	O
Turing	B-Architecture
machine	I-Architecture
on	O
the	O
Z3	B-Device
was	O
shown	O
in	O
1998	O
by	O
Raúl	O
Rojas	O
.	O
</s>
<s>
It	O
would	O
compute	O
all	O
possible	O
answers	O
,	O
but	O
the	O
unneeded	O
results	O
would	O
be	O
canceled	O
out	O
(	O
a	O
kind	O
of	O
speculative	B-General_Concept
execution	I-General_Concept
)	O
.	O
</s>
<s>
Rojas	O
concludes	O
,	O
"	O
We	O
can	O
therefore	O
say	O
that	O
,	O
from	O
an	O
abstract	O
theoretical	O
perspective	O
,	O
the	O
computing	O
model	O
of	O
the	O
Z3	B-Device
is	O
equivalent	O
to	O
the	O
computing	O
model	O
of	O
today	O
's	O
computers	O
.	O
</s>
<s>
From	O
a	O
practical	O
perspective	O
,	O
and	O
in	O
the	O
way	O
the	O
Z3	B-Device
was	O
really	O
programmed	O
,	O
it	O
was	O
not	O
equivalent	O
to	O
modern	O
computers.	O
"	O
</s>
<s>
This	O
seeming	O
limitation	O
belies	O
the	O
fact	O
that	O
the	O
Z3	B-Device
provided	O
a	O
practical	O
instruction	B-General_Concept
set	I-General_Concept
for	O
the	O
typical	O
engineering	O
applications	O
of	O
the	O
1940s	O
.	O
</s>
<s>
The	O
success	O
of	O
Zuse	O
's	O
Z3	B-Device
is	O
often	O
attributed	O
to	O
its	O
use	O
of	O
the	O
simple	O
binary	O
system	O
.	O
</s>
<s>
Zuse	O
,	O
however	O
,	O
did	O
not	O
know	O
of	O
Shannon	O
's	O
work	O
and	O
developed	O
the	O
groundwork	O
independently	O
for	O
his	O
first	B-Architecture
computer	I-Architecture
Z1	B-Device
,	O
which	O
he	O
designed	O
and	O
built	O
from	O
1935	O
to	O
1938	O
.	O
</s>
<s>
The	O
Tommy	O
Flowers-built	O
Colossus	B-Device
(	O
1943	O
)	O
and	O
the	B-Device
Atanasoff	I-Device
–	I-Device
Berry	I-Device
Computer	I-Device
(	O
1942	O
)	O
used	O
thermionic	O
valves	O
(	O
vacuum	O
tubes	O
)	O
and	O
binary	O
representation	O
of	O
numbers	O
.	O
</s>
<s>
The	O
ENIAC	B-Device
computer	I-Device
,	O
completed	O
after	O
the	O
war	O
,	O
used	O
vacuum	O
tubes	O
to	O
implement	O
switches	O
and	O
used	O
decimal	O
representation	O
for	O
numbers	O
.	O
</s>
<s>
Until	O
1948	O
programming	O
was	O
,	O
as	O
with	O
Colossus	B-Device
,	O
by	O
patch	O
leads	O
and	O
switches	O
.	O
</s>
<s>
The	O
Manchester	B-Device
Baby	I-Device
of	O
1948	O
along	O
with	O
the	O
Manchester	B-Device
Mark	I-Device
1	I-Device
and	O
EDSAC	B-Device
both	O
of	O
1949	O
were	O
the	O
world	O
's	O
earliest	O
working	O
computers	O
that	O
stored	O
program	O
instructions	O
and	O
data	O
in	O
the	O
same	O
space	O
.	O
</s>
<s>
In	O
2008	O
,	O
Horst	O
Zuse	O
started	O
a	O
reconstruction	O
of	O
the	O
Z3	B-Device
by	O
himself	O
.	O
</s>
