Formal Languages Questions
The main difference between a Turing machine and a pushdown automaton lies in their computational power and the type of memory they possess.
A Turing machine is a theoretical computing device that consists of an infinite tape divided into cells, a read/write head that can move along the tape, and a control unit that determines the machine's behavior. It has the ability to read, write, and erase symbols on the tape, and can perform an unlimited number of steps. Turing machines are capable of solving any problem that can be solved algorithmically, making them highly powerful and versatile.
On the other hand, a pushdown automaton (PDA) is a finite-state machine with an additional stack memory. It can read input symbols, change its state, and push or pop symbols onto/from the stack. The stack allows the PDA to remember and access previously processed symbols. PDAs are more limited in their computational power compared to Turing machines, as they cannot solve certain problems that require unbounded memory or non-deterministic behavior.
In summary, the key differences between a Turing machine and a pushdown automaton are the presence of an infinite tape and the ability to perform unlimited steps in a Turing machine, while a pushdown automaton has a finite stack memory and is more restricted in its computational capabilities.