Tape-based Turing Machines
Turing's a-machine model
Turing's (1936) a-machine (as he called it) was left-ended, right-end-infinite. He provided symbols əə to mark the left end. Any of finite number of tape symbols were permitted. The instructions (if a universal machine), and the "input" and "out" were written only on "F-squares", and markers were to appear on "E-squares". In essence he divided his machine into two tapes that always moved together. The instructions appeared in a tabular form called "5-tuples" and were not executed sequentially.
Read more about this topic: Turing Machine Equivalents
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