Deterministic Finite (-state) Automata

Informally, a DFA (Deterministic Finite State Automaton) is a simple machine that reads an input string -- one symbol at a time -- and then, after the input has been completely read, decides whether to accept or reject the input. As the symbols are read from the tape, the automaton can change its state, to reflect how it reacts to what it has seen so far.

Thus, a DFA conceptually consists of 3 parts:

1. A tape to hold the input string. The tape is divided into a finite number of cells. Each cell holds a symbol from .
2. A tape head for reading symbols from the tape
3. A control , which itself consists of 3 things:
   • finite number of states that the machine is allowed to be in (zero or more states are designated as accept or final states),
   • a current state, initially set to a start state,
   • a state transition function for changing the current state.