  Finite state machines (FSMs) are a theoretically and practically important
model of computation. We propose a general, thermodynamically consistent model
of FSMs and characterise the resource requirements of these machines. We model
FSMs as time-inhomogeneous Markov chains. The computation is driven by
instantaneous manipulations of the energy levels of the states. We calculate
the entropy production of the machine, its error probability, and the time
required to complete one update step. We find that a sequence of generalised
bit-setting operations is sufficient to implement any FSM.
