A*Turing machine*is the combination of a sequential, finite-state machine plus an external read/write memory storage medium called the*tape*(think of a ribbon of magnetic tape). The tape is a linear sequence of squares, with each square holding one of several possible symbols. Most generally, a Turing machine can have any number of different symbols it can recognize, but I’ll assume here that we are discussing the 2-symbol case (0 or 1). In 1956, Shannon showed that this in no way limits the power of what a Turing machine can do.

The tape is arbitrarily long in at

EP - 175 PB - Princeton University Press PY - 2013 SN - 9780691151007 SP - 161 T2 - The Logician and the Engineer T3 - How George Boole and Claude Shannon Created the Information Age UR - http://www.jstor.org/stable/j.cttq957s.12 Y2 - 2021/09/28/ ER -