Quote from Turing
I am slowly making my way through Andrew Hodges’ biography of Alan Turing, which I bought electronically last year (the Turing centennial year). It’s a great book, and is simultaneously teaching me about the history of computing machines, the history of cryptography, and World War 2, as well as about the title character. Here’s a part that I read today:
In general the arrangement of the memory on an infinite tape is unsatisfactory on a practical machine, because of the large amount of time which is liable to be spent in shifting up and down the tape to reach the point at which a particular point of information required at the moment is stored. Thus a problem might easily need a storage of 3 million entries, and if each entry was equally likely to be the next required the average journey up the tape would be through a million entries, and this would be intolerable. One needs some form of memory with which any required entry can be reached at short notice. This difficulty presumably used to worry the Egyptians when their books were written on papyrus scrolls.
This is part of a talk by Alan himself, from February 1947.
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