10.4 A UNIVERSAL TURING MACHINE

Consider the following argument against Turing’s thesis: “A Turing machine as presented in Definition 9.1 is a special-purpose computer. Once δ is defined, the machine is restricted to carrying out one particular type of computation. Digital computers, on the other hand, are general-purpose machines that can be programmed to do different jobs at different times. Consequently, Turing machines cannot be considered equivalent to general-purpose digital computers.”

This objection can be overcome by designing a reprogrammable Turing machine, called a universal Turing machine. A universal Turing machine Mu is an automaton that, given as input the description of any Turing machine M and a string w, can simulate the computation ...

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