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Imagine, 6 Tons of Punched Cards Every Week!

Posted by Craig H on 2 May 2015

An often neglected, but crucial, part of Bletchley Park’s work in World War II was the vast amount of data processing done using punched cards on Hollerith machines.  The department which did this was called the “Freebornery”, at first located in Hut 7 (since demolished) and later in Block C (recently restored as the new visitor centre).

There has been very little detail published on the day-to-day operations of the Freebornery, so I recently visited the National Archives and made a copy of a typewritten document they hold: “The Use of Hollerith Punched Card Equipment in Bletchley Park”.  With their kind permission, we are now publishing the text on our wiki for the benefit of researchers and other interested readers.

It is a well-known fact that, before electronic computers came along, very large volumes of data were processed using punched cards, for example the US national census data which Hollerith machines were originally designed to deal with. What may not be widely appreciated is the amazing complexity of the computations that could be done these machines, especially when the ingenious minds at Bletchley Park were applied to customising them and developing new processes.

Although I am (just 😉) old enough to have used card punches to key in mainframe computer programs, I have never seen electromechanical sorters, tabulators and so on in action. As the document describes, seeing an entire building filled with these huge, heavy, noisy machines all operating at full speed, each executing their own part of a massive computation, with stacks of cards being rushed by operators from one machine to another, must have been quite an experience; and then imagine that all day every day, using 2,000,000 cards every week! A back-of-the-envelope calculation suggests they must have had lorry loads of blank cards coming in almost daily, as 2 million cards weigh almost 6 tons 😯.

I hope that publishing this document will spark some interest in the forgotten art of large-scale electromechanical data processing. I’d love to see emulators of the different machines made available, and even better to see the real thing in action. The National Museum of Computing does have some surviving punched-card-processing machines (although not the models used in the Freebornery) which are being restored to working order; I look forward to seeing them!

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