How does a general automaton differ from a Turing machine?

In automata theory, the primary distinction between a general automaton and a Turing machine lies in the capacity of their memory storage.1

A general automaton, such as a modern electronic digital computer, is characterized by a memory-storage unit of a fixed, albeit potentially very large, size. In contrast, a Turing machine is defined as a general automaton to which an unbounded memory unit—typically represented as an infinitely extensible tape—has been added.21

This difference in memory design is critical to their computational power. Because the Turing machine possesses an unbounded tape, it can compute a wider class of functions than those obtainable by general automata with finite memory. Consequently, the Turing machine serves as a fundamental mathematical model for computability, establishing the theoretical limits of what can be calculated by any algorithmic method. While general automata are practical tools for implementing complex systems, the Turing machine remains the standard reference point for proving mathematical theorems regarding the nature of computation.134