W.D.Clinger
Philosopher
The first of those sentences is true, but what follows is balderdash.A Turing Machine is an abstract construct used in computational theory. A real, working version of this is necessarily finite. However, instead of being called a Finite Turing Machine it goes by the less intuitive name of Linear Bounded Automation. Any working computer we have today should be an LBA.
Turing machines start out finite and remain finite at every finite stage of computation. They are potentially infinite in that there is no bound on the size of their tape (memory). To build a real, working Turing machine, you build a machine with a finite tape that is dynamically extensible: Whenever the TM gets to the end of the tape, you add more tape, pretty much as you would add another memory device to your computer system or would replace one of your system's memory devices by a similar device with more capacity, copying the replaced device's contents onto the new one as you do so.
barehl tells us a Linear Bounded Automaton is finite, but the only bound on the size of a Linear Bounded Automaton's tape is derived from the size of its input. To build a real, working Linear Bounded Automaton, you have to build a machine with an arbitrarily long finite tape. You'd do that the same way you'd build a Turing Machine, but it's slightly simpler because you only have to add the additional tape (memory) once, when you are given a concrete input and can compute the amount of memory needed from the input's size.
It is silly to say, as barehl did, that today's working computers are Linear Bounded Automata rather than Turing machines. You can add new or larger memory devices to consumer-grade computers by plugging in a USB thumb drive. It is also possible to build computers that allow other kinds of memory devices to be added dynamically without shutting down the computer. The ability to do that is necessary if you're building a Linear Bounded Automaton, and once you've done it you've done all of the engineering necessary to construct a working Turing machine.
In the real world, the real reason real computers aren't equivalent to Turing machines is that their ability to address memory devices, even large hard drives, is typically limited by a fixed maximum number of bits used to identify the location/cell/sector/word/whatever you want to access on a memory device, and by the fixed number of bits used to identify the particular memory device you want to access. Both of those technical limitations could be overcome quite easily, but it's cheaper and faster to use a fixed number of bits that's believed to exceed the number of memory devices and the device capacities that will actually be used during the anticipated lifetime of the computer system.
A cognitive theory that's based on fundamental misconceptions about Turing machines and Linear Bounded Automata is unlikely to add to our knowledge of cognition or intelligence.
!