Turing on States and Instructions

Andrew Hodges. Alan Turing: The Enigma of Intelligence "The Spirit of Truth" p. 107 note

The arguments also implied two rather different interpretations of the machine 'configuration'. From the first point of view, it was natural to think of the configuration as the machine's internal state — something to be inferred from its different responses to different stimuli, rather as in behaviourist psychology. From the second point of view, however, it was natural to think of the configuration as a written instruction, and the table as a list of instructions, telling the machine what to do. The machine could be thought of as obeying one instruction, and then moving to another instruction. The universal machine could then be pictured as reading and decoding the instructions placed upon the tape. Alan Turing himself did not stick to his original abstract term 'configuration', but later described machines quite freely in terms of 'states' and 'instructions', according to the interpretation he had in mind. This free usage will accordingly be employed in what follows

In Turing's model the moves are simple. A symbol being scanned can be changed, erased or remain unchanged; the machine can move to observe another segment (square); the machine can remain in the same configuration or change to some specified configuration. Past moves determine future moves; a state may also be treated as an instruction.

In some ways this is like reading a text.

And so for day 693
05.11.2008