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and above all relatively slow. By replacing them with completely elec-
tronic components, Eckert and Mauchly were able to dramatically speed
up the process of computation. Whereas the electromechanical Harvard
Mark I (completed in 1943), which was of similar complexity to the
ENIAC, could perform 2 or 3 additions per second, and a multiplication
every six seconds, the ENIAC (completed just three years later) could
perform 5,000 additions per second, or 333 multiplications. Although
this extraordinary improvement in performance came at the price of
increased cost and complexity—when completed the ENIAC weighed
nearly thirty tons, occupied an entire room, and required more than
eighteen thousand expensive and unreliable vacuum tubes—by the end
of the 1940s it was clear that electronic computing was the wave of
the future.
The second revolutionary feature of the ENIAC was its ability to be
programmed. This meant that the machine could be reconfi gured to
perform different types of computation. In the case of the ENIAC the
machine had to be physically wired, or “set up,” as the process was
called at the time, to compute specifi c functions—a complicated process
that could take as long as two days.
12
Within a short time, however, the
ENIAC was modifi ed to allow it to be “programmed” automatically
using punch cards.
13
In the meantime, the physicist and mathematician
von Neumann had published his now-infamous
First Draft of a Report
on the EDVAC
, which provided a description of the computer that was
to be heir to the ENIAC.
14
This successor machine, which was called the
Electronic Discrete Variable Automatic Computer (EDVAC), was the
world's fi rst stored-program computer. Unlike previous programmable
machines, the EDVAC stored-program computer did not distinguish
between data and instructions. This allowed it to modify its own instruc-
tions, which effectively allowed the computer to program itself. This not
only allowed for greater fl exibility in programming but also paved the
way for the development of assemblers, compilers, and other program-
ming tools. The concept of the stored-program computer was so signifi -
cant that it has come to defi ne the essence of the modern computer; today
a device is only considered to be a true computer if it is a stored-program
machine.
And this is what brings us back to the centrality of software to the
history of computing: it was not so much the original invention of the
electronic computer that launched the computer revolution but the later
discovery that such computers could be made programmable. To be sure,
prior to the electronic computer there were machines that could be
