## Two Heads are Better than Two Tapes (1994)

Citations: | 10 - 6 self |

### BibTeX

@MISC{Jiang94twoheads,

author = {Tao Jiang and Joel I. Seiferas},

title = {Two Heads are Better than Two Tapes},

year = {1994}

}

### OpenURL

### Abstract

. We show that a Turing machine with two single-head one-dimensional tapes cannot recognize the set f x2x 0 j x 2 f0; 1g and x 0 is a prefix of x g in real time, although it can do so with three tapes, two two-dimensional tapes, or one two-head tape, or in linear time with just one tape. In particular, this settles the longstanding conjecture that a two-head Turing machine can recognize more languages in real time if its heads are on the same one-dimensional tape than if they are on separate one-dimensional tapes. 1. Introduction The Turing machines commonly used and studied in computer science have separate tapes for input/output and for storage, so that we can conveniently study both storage as a dynamic resource and the more complex storage structures required for efficient implementation of practical algorithms [HS65]. Early researchers [MRF67] asked specifically whether two-head storage is more powerful if both heads are on the same one-dimensional storage tape than if t...