 Turing also showed that there are universal TMs—machines that can compute any function computable by any other TM. Universal machines do this by executing instructions that encode the behavior of the machine they simulate. Assuming the Church-Turing thesis, universal TMs can compute any function computable by algorithm. This result is significant for computer science: you don’t need to build different computers for different functions; one universal computer will suffice to compute any computable function. Modern digital computers are universal in this sense: digital computers can compute any function computable by algorithm for as long as they have time and memory. (Strictly speaking, a universal machine has an unbounded memory, whereas digital computer memories can be extended but not indefinitely, so they are not unbounded.)