## Home-Built Turing Machine 123

stronghawk writes

*"The creator of the Nickel-O-Matic is back at it and has now built a Turing Machine from a Parallax Propeller chip-based controller, motors, a dry-erase marker and a non-infinite supply of shiny 35mm leader film. From his FAQ: 'While thinking about Turing machines I found that no one had ever actually built one, at least not one that looked like Turing's original concept (if someone does know of one, please let me know). There have been a few other physical Turing machines like the Logo of Doom, but none were immediately recognizable as Turing machines. As I am always looking for a new challenge, I set out to build what you see here.'"*
## I found that no one had ever actually built one (Score:1, Interesting)

I think you'll find that every single computer ever made has been a Turing machine.

## Re:You're Doing It Wrong (Score:3, Interesting)

Couldn't that be said of any Turing machine? Whatever you build it out of is Turing-complete, I think.

## Re:You're Doing It Wrong (Score:4, Interesting)

## Re:Technically... (Score:5, Interesting)

## Re:Technically... (Score:3, Interesting)

Well, if you want to split hairs, at least split them to the end...

Eventually, of course, the universe will run out of mass for you to make tape out of, but the machine is still a proper Turing machine.

How is this "still a proper Turing machine"? There are programs that would work on a theoretical Turing machine (with arbitrary amount of tape), but would run out of memory in your scheme.

The OP point stands: we will never actually be able to build a real Turing machine[1]. Still, computers are very good approximations (for programs that require up to a certain amount of memory).

[1] Assuming the universe is actually expanding and that the theory of relativity is right (a good discussion can be found here: http://www.scottaaronson.com/democritus/lec20.html [scottaaronson.com])

## Re:hmmm (Score:5, Interesting)

## So you haven't seen this? (Score:2, Interesting)

http://www.youtube.com/watch?v=cYw2ewoO6c4&feature=fvst [youtube.com]

## Re:Non-infinite (Score:1, Interesting)

## Re:Cool...I think. (Score:3, Interesting)

Personally, having been entirely fascinated with Turing and his work during my college years (from a mathematical point of view - the Entscheidungsproblem [wikipedia.org] rather than CS), seeing an actual Turing machine sends shivers up my spine. Kudos!

For anyone interested in knowing more about this fascinating scientist, I recommend the book by Andrew Hodges [amazon.com].

## Re: I found that no one had ever actually built on (Score:3, Interesting)