A Turing Tale


21 August 2014

This post contains extra information about my CACM article `A Turing Tale' (October issue, 2014), specifically regarding particular book chapters and page numbers for the source citations appearing in my article.

Below, I present fragments of my article along with precise source citations which were omitted due to editorial styling conventions.

In my section entitled "Hodges":

  • Also in a world without Turing, his universal machine would have come to light in one form or another and in no small part due to Emil Post, even though Post's "worker" model did not include a "universal machine" construction. [9,p.125]
  • One hundred years before Turing, Babbage had already planned for storing numbers in a machine that was universal, as he and Ada (Countess of Lovelace) were well aware. [9,p.297-298]
  • In America, Eckert and Mauchly perceived the idea of storing instructions inside the machine, in electronic form. [9,p.302]
  • Von Neumann may or may not have been influenced by Turing when working on the ENIAC-to-EDVAC transition. [9,p.303]

Hodges stressed throughout his book that Turing was not taken seriously by most of his contemporaries in the arena of computer building. [9,p.353,367,395]  Turing's 1936 paper meant a lot to him and to some of his close colleagues, as Charles G. Darwin's repeated statements in 1946 about the ACE machine illustrate. [9,p.336,348,349]  That said, Turing's paper had little impact on the computer-building community at large. [9,p.408,440]

In what respect, then, did Turing stand out in the 1940s?

Turing had the remarkable ability to unify seemingly disparate theoretical and practical concepts. He needed just one tape in his 1936 paper and just one electronic memory in the 1940s. In Hodges's words: "This [unification of data and instructions] was the new idea, ... For it threw all the emphasis on to a new placethe construction of a large, fast, effective, all-purpose electronic `memory.' And in its way it made everything much more simple, less cluttered in conception." [9,p.303]


Based on his 1936 universal machine, Turing was able to see that one machine could do the job of several special-purpose machines. [9,p.293]


As Hodges implicitly conveyed, storing instructions externally (on, say, paper tape) or internally (in computer memory) does not matter in terms of Turing's universality. [9,p.297-298]


In my section entitled "Davis and Copeland":

To set the stage for Turing, Davis refers to a tiny excerpt from Babbage's writingswhich states that his analytical engine "could do everything but compose country dances"to conclude that Babbage had a limited view on universality. [4,p.123-124]

Davis also puts Turing on a pedestal by ridiculing the following 1955 statement of the computer pioneer Howard Aiken: "If it should turn out ... .... I have ever encountered." [4,p.124]


In Davis's words: "If Aiken had grasped the significance of Alan Turing's paper, published two decades earlier, he would never have made such a preposterous statement." [4,p.124]


Davis also notes that "Turing's universal computer was a marvelous conceptual device," which is of course true, and then continues as follows: "But could one actually build such a thing?... These questions were in Turing's mind from the very first." [4,p.151]  Hodges, by contrast, has cautioned his readership not to blindly believe that Turing set about constructing a universal machine before the war. [9,p.532]


Copeland misleadingly describes "the stored-program universal computer" as a "single invention" from 1936 [2,p.3]a statement that both Hodges and Davis have complained about. [4,p.147,166][10,p.1994]

"Computer science textbooks," Copeland says, "often attribute Turing's stored-program concept to von Neumann." But, Copeland insists, von Neumann "never claimed it as his own." [2,p.130]  Copeland then continues: "On the contrary, von Neumann said that Turing's `great positive contribution' was to show that `one, definite mechanism can be universal.'" [2,p.130]


Davis relies on Time magazine to make a case for Turing. [4,p.171-172]  Copeland, in turn, writes: "Many people have acclaimed von Neumann as the `father of the computer,' von Neumann's friend Stanley Frankel observed, "but I am sure that he would never have made that mistake himself." [2,p.130-131]



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