Turning Machine

The Turing Machine is an abstract machine introduced in 1936 by Alan Turing to give a mathematically precise definition of algorithm (or “mechanical procedure”).
Each Turing machine can be viewed as a specifically programmed computer.
A Turing Machine is a kind of state machine, which has an infinite one-dimensional tape divided into cells.
The machine has a read-write head, which at any time scanning a single cell on the tape. This read-write head can move left and right along the tape to scan cells.
The machine is determined completely by (1) its current state, (2) the symbol in the cell currently being scanned and (3) a table of transition rules, which serve as the “program” for the machine.
Each transition rule is a 4-tuple: < State0, Symbol, Statenext, Action >
The actions available are either to write a symbol on the tape in the current cell, or to move the head one cell to the left or right.

以上命題係叫做 "Church-Turing thesis"

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