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anyone had expected. The calculational speed of the ENIAC was impressive - it
was more than a thousand times faster than Aiken's Mark I machine. On ten-
digit numbers, the machine could calculate more than five thousand additions
or three hundred multiplications per second! However, although this was very
much faster than the differential analyzer and the Mark I in terms of its basic
operations, it still took about two days to set up the ENIAC to solve a specific
problem - and this was after the operators had written a program specifying
the correct sequence of operations.
Writing an ENIAC program required the programmer to have almost as
much knowledge of the machine as its designers did ( Fig. 1.7 ). The program was
implemented by setting the ENIAC's switches to carry out the specific instruc-
tions and by plugging in cables to arrange for these instructions to be executed
in the correct order. The six women who did most of the programming for the
ENIAC were finally inducted into the Women in Technology International Hall
of Fame in 1997 ( Fig. 1.8 ).
The first problem to be performed by the ENIAC was suggested by von
Neumann. The problem arose from his work at Los Alamos and involved the
complex calculations necessary to evaluate a design for Edward Teller's pro-
posed hydrogen bomb. The results revealed serious flaws in the design. Norris
Bradbury, Director of the Los Alamos Laboratory, wrote a letter to the Moore
School saying, “The complexity of these problems is so great that it would have
been impossible to arrive at any solution without the aid of ENIAC.” 4
Fig. 1.6 The ENIAC on a chip. This
chip was designed to mark the fiftieth
anniversary of the ENIAC project by a
group of students at the University of
Pennsylvania. This 0.5 cm 2 chip can do
the same computations as the original
30-ton computer in 1946. No other tech-
nology in the course of human history
has achieved this pace of development.
Von Neumann and the stored-program computer
After the ENIAC design was finalized and the machine was being built,
Eckert and Mauchly had time to think about how they could design a better
computer using new memory storage technologies. It had become clear to
them that the ENIAC needed the ability to store programs. This would enable
programmers to avoid the lengthy setup time. Eckert and Mauchly probably
came up with this idea for a stored-program computer sometime in late 1943 or
early 1944. Unfortunately for them, they never got around to explicitly writ-
ing down their ideas in a specific design document for their next-generation
computer. There are only some hints of their thinking in their progress reports
on the construction of the ENIAC, but there now seems little doubt that they
deserve at least to share the credit for the idea of the stored-program computer.
When von Neumann first arrived at the Moore School in September 1944, he
was briefed by Eckert and Mauchly about their ideas for a new machine they
called EDVAC - Electronic Discrete Variable Computer. According to Mauchly's
account, they told von Neumann the following:
We started with our basic ideas: there would be only one storage device (with
addressable locations) for the entire EDVAC, and this would hold both data
and instructions. All necessary arithmetic operations would be performed in
just one arithmetic unit (unlike the ENIAC). Of course, there would be devices
to handle input and output, and these would be subject to the control module
just as the other modules were. 5
Fig. 1.7 U.S. Army ENIAC poster. The
ENIAC was advertised as a work oppor-
tunity for mathematicians and puzzle
solvers.
In the months that followed, the three of them refined their ideas for the
EDVAC, which eventually resulted in von Neumann writing a paper, titled the
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