&gt;  make extensions on the original. use the single tape to simulate multiple tapes, one for stack(or registers), one for ram, one for rom, and another for encoding how the hardware behaves against the other tapes.<p>Very nice; that is surely about the best information:length ratio one could hope for!  I hope you won&#x27;t mind a slight clarification—obvious, I am sure, to you and to any computer scientist, but not, perhaps, to a non-specialist:  this is <i>not</i> an extension of the original, but rather a <i>simulation</i> within the original of an apparently more general concept.  This is important, because it means that any theoretical results about the original concept also apply to its apparent generalisation (e.g., multi-tape Turing machines still can&#x27;t decide undecideable problems).