1. A channel adaptive iterative turbo decoder system comprising: first and second maximum a posteriori (“MAP”) decoders for iteratively computing: (i) a set of branch metrics for a window of received data bits, (ii) forward recursive path state metrics for the window, (iii) reverse recursive path state metrics for the window, and (iv) from the forward and reverse recursive path state metrics, a log likelihood ratio (“LLR”) for 1 and 0 for each data bit in the window; an iteration counter for counting a number of iterations performed by at least one of the MAP decoders; and a non-convergence detector for, only after a predetermined channel-dependent number of iterations, identifying those data bits in the window of received data which are non-convergent to 0 or 1 and enabling at least one of the first and second MAP decoders to compute: (i) a set of branch metrics for the received data, (ii) forward recursive path state metrics for the window, (iii) reverse recursive path state metrics for the window, and (iv) from the forward and reverse recursive path state metrics, the LLR for 1 and 0 for only the non-convergent data bits.