I was going to ask a similar question myself. Given the massive increase in computing performance since the A320 was introduced, is the system hardware and software updated at any stages to take advantage of this. Presumably, the entire control systems would have to be retested exhaustively before these changes could go live. Maybe it is just easier to stick with old technology until the next generation arrives? Also, given the time difference between them, would there be many differences in the hardware / software of, say, the A321, A320, A319 or A318?