Compact realization of reversible turing machines by 2-state reversible logic elements

Abstract

A reversible logic element with memory (RLEM) is a primitive by which reversible computing systems can be constructed. Different from a reversible logic gate, it has a finite memory, and thus is defined as a kind of reversible sequential machine (RSM). It is known that any reversible Turing machine (RTM) can be built in a simple way using a rotary element (RE), a typical 2-state RLEM (i.e., having 1-bit memory) with four input/output lines. In this paper, we show another compact realization of an RTM using a 2-state RLEM No. 4-31 with four input/output lines. Since RLEM 4-31 can be simulated by a circuit composed of only two copies of 2-state RLEM 3-7, we also obtain another compact realization by an RLEM with three input/output lines. © 2014 Springer International Publishing Switzerland.