ENIAC's 75th anniversary

ENIAC was quite a limited machine, and yet in 1949 it was used to compute π to over 2000 digits. The end result was the paper “The ENIAC’s 1949 Determination of π” (pdf)

There’s a writeup here, where the author explains a bit, having reverse-engineered and re-implemented the approach for a 2012 paper (IEEE link).

After its unveiling the ENIAC was moved to the Ballistics Research Lab in Aberdeen Maryland. And while it was used for government work, there was an open policy that allowed the ENIAC to be used for pure research. It was during this time that the ENIAC was modified so it could be programmed using numerically-coded instructions entered into its function tables instead of having to laboriously re-wire the ENIAC to perform a calculation.

… I got interested in the question because the ENIAC being a primitive computer (though in its time it was cutting-edge) really wasn’t designed to perform a calculation that required dividing by numbers up to 2000 digits long. To understand the magnitude of the problem facing Reitswiesner and his team, one needs to understand the architecture of the ENIAC. The 40 panels of the ENIAC made up 30 separate units: twenty of these were accumulators each capable of storing a 10 digit decimal number plus sign – making the total storage of the ENIAC 200 decimal digits.

From the 2012 paper:

From the 1950 paper:

Since the possibility of official time was too remote for consideration, permission was obtained to execute these projects during two summer holiday week ends when the ENIAC would otherwise stand idle, and the planning and programming of the projects was undertaken on an extra-curricular basis by the author.

and

The cards bearing the remainders then were fed into the ENIAC reader, and the entire process was repeated for the next i digits, the ENIAC reading each remainder in turn and placing it before the digits of the appropriate term.

via this short series of posts.

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And 75 years later, we have PI compute a Einac.