Show HN: Turing machine simulator in C 11 years ago
The important point is that a TM is capable to calculate everything that is considered to be decidable. It is _the_ computation machine in theoretical CS and different models (eg lambda calculus) are equivalent in computational power. Implementations are a proof-of-concept to show/visualize their power and can be seen as compilers for basic languages.
Their exact mathematical description differs from source to source but the interesting thing is that just a small program (the TM) is capable of calculating everything (efficiency is not the question here).