Computing Machinery and Intelligence

4 Digital computers

1. How did Turing explain the idea of a digital computer?
   As a machine meant to carry out any operation a human computer could do: someone following fixed rules from a book without deviating, with unlimited paper for calculations.
   • Turing, 1950, Computing Machinery and Intelligence (Mind), §4
2. What are the three parts of a digital computer in Turing’s description?
   The store (the human computer’s paper and memory, including the instruction table), the executive unit (performs individual operations) and the control (makes sure instructions are obeyed correctly and in order).
   • Turing, 1950, Computing Machinery and Intelligence (Mind), §4
3. Why are conditional jump instructions so important?
   They let a sequence of operations be repeated until some condition holds, obeying the same instructions over and over rather than fresh ones each time. (Turing’s analogy: a notice in the hall telling Tommy to check on the shoes each morning, instead of asking him afresh.)
   • Turing, 1950, Computing Machinery and Intelligence (Mind), §4
4. What did Turing mean by “programming”?
   Constructing instruction tables: to programme a machine to do A means putting the appropriate instruction table into it. To mimic a human computer one asks him how the operation is done and translates the answer into an instruction table.
   • Turing, 1950, Computing Machinery and Intelligence (Mind), §4
5. Why is it irrelevant that computers and nervous systems both use electricity?
   Babbage’s Analytical Engine was purely mechanical, and all digital computers are in a sense equivalent, so electricity can’t be of theoretical importance; it just appears wherever fast signalling is needed. Look for mathematical analogies of function instead.
   • Turing, 1950, Computing Machinery and Intelligence (Mind), §4