Alan Turing's famous machine is an abstract automaton that can be in any one of a number of states and that is capable of moving back and forth on an infinitely long tape of instructions (customarily zeros and ones), reading and writing instructions on each segment of tape as it moves. A Turing machine's state at a given time is a finite function of both the machine's current state and the information on the currently scanned section of tape. A universal Turing machine is a Turing machine capable of executing any algorithm.