Listen how Jim Massey describes the true story of Andrew Viterbi's paper on
what was later called the Viterbi Algorithm.
Jim Massey again. He describes the problem of the complexity of the Viterbi
decoder.
Let's forgive Peter Massey, author of the fairy tale, this technical inaccuracy:
he uses an alphabet of 10 symbols and a convolutional encoder of 2 memory elements.
In such case, the number of states of the encoder is 10 times 10 = 100, so
the decoder of "Vivian Terby" needs a trellis of width 100. In Peter's
story she only uses a state space of 10 instead of 100.