After graduating with my BSEE and getting my first professional job, one of my very first tasks was to implement this algorithm on a PDP 11, in assembly. I first implemented it in Fortran (C had just come out and I didn't know it yet) to run on a VAX 11/780. Once it was working, it was amazing to see how powerful it was in correcting noisy data, even using rate 1/2 coding and short constraint lengths. Consider that the Voyager spacecraft, now nearly 24 billion miles from earth, uses it and it is still possible to decode it's data. In my mind, Viterbi's algorithm is equal in importance in communications with the FFT.