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July 2020

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New evidence re von Neumann's view of Turing in 1945
by thomas.haigh＠gmail.com 02 Jul '20

02 Jul '20

Hello SIGCIS, ACM has turned off its free access to the digital library, but I did notice that my most recent Communications of the ACM column is still open access and that reminded me that I never sent out an alert when it was published back in January. Title: "Von Neumann Thought Turing's Universal Machine was 'Simple and Neat.': But That Didn't Tell Him How to Design a Computer" https://cacm.acm.org/magazines/2020/1/241712-von-neumann-thought-turings-uni versal-machine-was-simple-and-neat/fulltext It is written with Mark Priestley, based on a document that Mark found on a visit to the (newly catalogued) Herman Goldstine papers at the American Philosophical Society to gather material for his recent book, Routines of Substitution. Those of you who have been in the field for a while or tend to the computer science side may know that the question of whether von Neumann had read Turing's classic paper introducing Turing machines (1936) when he was writing "First Draft of a Report on the EDVAC" and initiating the design of the computer at the Institute for Advanced Studies (1945-6) has been much discussed, particularly by people trying to show that the fundamental idea of what is often called the "stored program computer" was somehow stolen from Turing. We always thought that discussion was a little off base, because I've never seen anyone identify an architectural features that appear in both the First Draft version of EDVAC and in Turing's paper that von Neumann wasn't independently exposed to in other contexts (his wide-ranging work in logic, the ENIAC project and the ideas of its members, the Harvard computer group, Bell Labs, etc.) (See my earlier column on this: http://www.tomandmaria.com/Tom/Writing/CACMActuallyTuringDidNotInventTheComp uter.pdf) Also there was no reason to doubt that von Neumann had read the paper back in the 1930s even though the earliest proof of his knowledge came from November 1946. There is an indirect link via a paper by McCullouch and Pitts which introduces the pseudo-neuron notation for what we'd now think of as logic gates, which von Neumann adapted for the First Draft. Providence and careful archival work delivered to Mark's a document headed "High Speed Computing" and written in the form of a lecture to a general audience or beginning of a primer on computer technology. We believe it comes from mid-1945 in which von Neumann discusses his thoughts on Turing's universal machine and on what the calls "The Logic of Pitts" and their usefulness for computer designers. This contains what may be the first discussion of the universal Turing machine by anyone other than Turing (Church's famous review synopsis named the "Turing machine" but does not focus on the universal machine - thanks to Andrew Hodges, who knows a lot more about Turing than we do, for highlighting this point to us). In fact von Neumann's summary is so similar to what you'd find in later textbooks that it takes an effort of historical will to remember how unusual this was in 1945. (For reasons we describe in the paper, we believe that this material was written just after the First Draft). On the other hand, the text also shows that while von Neumann was understandably impressed with Turing's work, he didn't think it a useful template for the construction of an actual machine: "Here the analogy to a high-speed computing machine breaks down, for one cannot wait for the machine to go all eternity for his answer." So he moved on to the Pitts neuron notation, showing how it could be used to describe the building blocks of digital logic. In an effort to figure out when this text was written and whether it was delivered, we found an article of Calvin Moores in Annals, and I followed up with a look at his diary and papers at CBI. This revealed a dated journal entry from October 28, 1945 in which von Neumann gave a similar ad-hoc lecture to visitors from the Naval Ordnance Lab's computer project, discussing Turing's paper, Pitts' neuron notation, and his ongoing work on instruction set design. As far as I know, this is the earliest dated reference by von Neumann to Turing's paper. How people interpret this new evidence will probably depend on their previous convictions. We point out that the fact that von Neumann could summarize Turing's paper so well but ignored it in other work of the period confirms that he compartmentalized it separately from his work on computer architecture, instead lumping it with his passionate but unfinished work on cellular automata in which context he freely acknowledge his debt to Turing. So we try and thread the needle by acknowledging the importance of the discovery without buying into the idea that this is the great unsolved mystery of early computing. Those who think that EDVAC was someone a slightly more practical Turing Machine will seize on von Neumann's suggestion that Turing's "system of logic could be used in building a computing machine" and that "The problem of developing a computing machine can be considered as a problem in logic." (Hmm, and then we can all argue about what "logic" means there - is it in the sense of "digital logic" or "switching logic," or the "logical control" von Neumann brings up in the next sentence, or does it privilege abstraction?) There's also the perplexing question of what the text was supposed to be. It is split into three very short "lectures", with the first two giving background and basic technologies and the third exploring Turing and Pitts. We suspect that the payoff would have come in later, unwritten lectures where von Neumann built on these lectures to introduce the new approach he'd taken in the First Draft and his ongoing work at IAS, just as he did in person when Moores called. If the lectures were supposed to be delivered at a specific venue we weren't able to identify it. The timeline doesn't seem to fit for the proto-cybernetic meetings going on around that time, and he is coy about things connected to ENIAC that were shared openly with that community. I could imagine him delivering them at some kind of Los Alamos colloquium. I even imagined him spending a train ride sketching out the first pages of what was supposed to be a popular science text on the emerging technology, following a similar impulse to his Los Alamos colleague George Gammow in One Two Three Infinity (published 1947) but Mark is not at all convinced by that idea. To me it explained the conceit of addressing the concerns of a computer designer while assuming none of the background knowledge a real computer designer would have. Best wishes, Tom

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