What's a Turing machine?

Question

What is a Turing machine and why do people keep mentioning it? My IBM PC is all I need to do my computation! Why does anyone care about these machines?

Answer 1

A Turing-machine is a theoretical machine that can be used to reason about the limits of computers. Simply put, it is an imaginary computer with infinite memory.

We care about Turing-machines because they help us discover what is impossible to accomplish with real computers (like your IBM PC). If it is impossible for a Turing machine to perform a particular computation (like deciding the Halting Problem), then it stands to reason that it is impossible for your IBM PC to perform that same computation.