Turing Machine - Additional Details Required To Visualize or Implement Turing Machines

Additional Details Required To Visualize or Implement Turing Machines

In the words of van Emde Boas (1990), p. 6: "The set-theoretical object provides only partial information on how the machine will behave and what its computations will look like."

For instance,

• There will need to be many decisions on what the symbols actually look like, and a failproof way of reading and writing symbols indefinitely.
• The shift left and shift right operations may shift the tape head across the tape, but when actually building a Turing machine it is more practical to make the tape slide back and forth under the head instead.
• The tape can be finite, and automatically extended with blanks as needed (which is closest to the mathematical definition), but it is more common to think of it as stretching infinitely at both ends and being pre-filled with blanks except on the explicitly given finite fragment the tape head is on. (This is, of course, not implementable in practice.) The tape cannot be fixed in length, since that would not correspond to the given definition and would seriously limit the range of computations the machine can perform to those of a linear bounded automaton.