Prerequisite – Turing Machine
1. Multiple track Turing Machine:
- A k-tack Turing machine(for some k>0) has k-tracks and one R/W head that reads and writes all of them one by one.
- A k-track Turing Machine can be simulated by a single track Turing machine
2. Two-way infinite Tape Turing Machine:
- Infinite tape of two-way infinite tape Turing machine is unbounded in both directions left and right.
- Two-way infinite tape Turing machine can be simulated by one-way infinite Turing machine(standard Turing machine).
3. Multi-tape Turing Machine:
- It has multiple tapes and controlled by a single head.
- The Multi-tape Turing machine is different from k-track Turing machine but expressive power is same.
- Multi-tape Turing machine can be simulated by single-tape Turing machine.
4. Multi-tape Multi-head Turing Machine:
- The multi-tape Turing machine has multiple tapes and multiple heads
- Each tape controlled by separate head
- Multi-Tape Multi-head Turing machine can be simulated by standard Turing machine.
5. Multi-dimensional Tape Turing Machine:
- It has multi-dimensional tape where head can move any direction that is left, right, up or down.
- Multi dimensional tape Turing machine can be simulated by one-dimensional Turing machine
6. Multi-head Turing Machine:
- A multi-head Turing machine contain two or more heads to read the symbols on the same tape.
- In one step all the heads sense the scanned symbols and move or write independently.
- Multi-head Turing machine can be simulated by single head Turing machine.
7. Non-deterministic Turing Machine:
- A non-deterministic Turing machine has a single, one way infinite tape.
- For a given state and input symbol has atleast one choice to move (finite number of choices for the next move), each choice several choices of path that it might follow for a given input string.
- A non-deterministic Turing machine is equivalent to deterministic Turing machine.